Technical
Tips and Tidbits for Owners of Isuzu Automobiles
Index
Simple MAF modification for I-TEC equipped Isuzu vehicles with
Bosch/Hitache LH-Jetronic Fuel Injection; G200, 4ZC1, and 4ZD1 Engines:
Ben Watson, in How to Tune and Modify Bosch Fuel Injection, outlines a
simple and free way to improve air flow into the engine by
modifying the mass air flow sensor. The MAF on I-TEC equipped
vehicles (all Impulse JR) is attached to the rear of the air
filter box, between the filter element and the throttle body. It
senses the change in air tempature ,from its inlet to its
outlet,to measure the air flow and tell the computer how much fuel
is required. The front of the MAF has a screen to prevent foriegn
matter (bugs, rocks,leaves,etc.) from entering the engine. But as
already described, this is BEHIND the air filter. Unless you are
extremely negligent and run without an air filter element, or have
trouble with varmints crawling into your air inlet, up into your
engine, this screen is totally retorical and unneeded, and serves
to do nothing but restrict air flow. The screen is much coarser
than the filter element and is only there to protect those who are
not responsible enough to care for their engine. Removing the
screen yields a considerable increase in air flow.
Fuel Injector Care:
Automotive manufacturers recomend that the fuel injectors be removed and
professionally cleaned every 50,000 to 70,000 miles. This is
because contaminated gasoline is a fact of life and deposits build
up on fuel injectors no matter how many additives or fuel cleaning
agents that you use. Deposits can clog injectors 20-30% or more
at 100,000 miles, reducing the power output of the vehicle by the
same amount. Remove your injectors and have them professionally
cleaned, calibrated, and blueprinted if you haven't already. Most
shops will return your injectors with a computer printout that
will tell you just how badly they were clogged. If you have the
injectors cleaned without removing them, the flow rate can not be
measured and the result can not be quantified or qualified.
EGR Bypass Tool; For G200, 4ZC1 and 4ZD1 Engines:
The EGR Bypass tube goes from the exhaust manifold, behind the engine,
and into the intake plenum/common chamber, where it is activated
by the EGR valve by the engines vacume. The system is designed to
reduce the amount of usable oxygen in the intake charge by
recirculating exhaust gases into the engine to reduce the engines
opperating temperature by roughly 500 degrees, and there by reduce
nitrogen oxide. Anyone who has taken off either of the manifolds
realizes just how chalenging the end fittings of the bypass pipe
are to unthread and especially rethread. This part was obviously
installed before the engine was put into the vehicle, because
there is no room to move a full sized wrench in the engine
compartment to work the fitting. The solution is to obtain a 22
mm or 7/8 inch end wrench that you aren't particularly attached to
and cut it down to about 5 1/2 inches in length. this will give
you plenty of room to unthread and thread the pipe fittings.
Ignition Timing:
Stock setting for the ignition timing on the Impulse JR is at 12 degrees
BTDC. This is a rather conservative setting. The timing can be
advanced some without fear of detination, and advancing the timing
will improve low end response and power. The timing can safely be
advanced as far as 16 degrees BTDC, be careful if you go beyond
this point.
Idle Speed; For G200, 4ZC1, and 4ZD1 Engines:
Stock idle speed is set at 850 to 950 RPM. This setting yields
sluggishness off the line when accelerating. Raising the idle
setting to 1000 to 1100 RPM will significantly reduce this
sluggishness and alieviate much of the "rev and drop" symptom that
is common in the Impulse JR.
Engine Idle Speed Problems:
Eratic Idle Speed:
Isuzu engines commonly exhibit eratic idle problems, the engine revving
and dropping in rpms, sometimes dropping almost to the point of dying.
There are several things that can cause this problem:
Leaks in the vacume hoses or aged, cracked hoses can let in air that is
not being metered by the ECU's sensors.
Leaking or sticking EGR Bypass valve may be allowing exhaust gasses into
the intake when the engine is not under load (idling).
Loose electrical connections in the engine sensors can cause problems.
On G200, 4ZC1, and 4ZD1 Engines:
The Idle Control Valve / Idle Solenoid may
not be functioning properly.
On 4XC1, 4XE1, and 4XF1 Engines:
These engines are notorious for idle speed
revving and dropping. Thusfar, no single simple answer has been sucessful
in all situations has been offered.
Before you do anything at all, check the ignition timing and reset it to
factory specifications (9-11 degrees). Incorrectly adjusted ignition
timing (too far advanced timing), will cause havoc within the ECU and
the engine will not idle correctly.
After this, the first step would be to carefully remove the IAC control valve
and clean it with carburettor cleaner, xylene, or some other solvent and a tooth
brush.
Also clean the passages in the throttle body, and then reinstall the IAC
valve, making sure to reinstall the O ring also. This may resolve the
problem in some very mild cases.
Check the throttle cable adjustment. If the throttle cable is adjusted too
tight, the throttle position senesor will not read that the throttle is closed
at idle, and this will cause the computer to fight to lower the idle speed.
Make sure there is some slack in the line and that the throttle arm easily and
consistently rests against the throttle adjustment screw whenever there is
no pressure on the pedal. If it does not, then examine, repair, or replace the
throttle cable and gas pedal if anything is found in either of these assemblies
to show the cable or pedal is sticking.
If this does not help, things get much more complicated. These engines are
set up with a learning mode and the computer controls all functions, including
idle speed, based on the signals fromt he sensors. If one sensor begins to
malfunction but does not go totally dead, the computer will continually try
to adjust, causing all sorts of symptoms, and even running the trouble codes
will not help, because it will show nothing unless the sensor is dead.
The best and easiest solution is to have a service department use a scan
tool to determine the problem. Anything else would be a futile effort to
guess and get lucky on what the problem is and pray that you don't waste
hundereds of dollars replacing sensors that are not defective.
The throttle position sensor on these vehicles can not be adjusted. This does
not mean that the sensor can not be twisted on its mounting bolts so that the
baseline voltage reading is different, it means that the baseline voltage reading
is meaningless, and the computer takes whatever the lowest voltage reading
sensed to be 0%, no matter what that voltage may be. Using the scan tool and
observing the physical position of the throttle linkage at the throttlebody,
observe that the percentage reading does not always return to 0 though the linkage
has physically returned to its fully closed position. This appears to be a
voltage variance in the sensor signal from teh ECU. The voltage sent to the
sensor from the ECU increases above idle speed above the 5 volts specified, and
though the linkage and sensor return to the fully closed position, the increased
voltage in the sensor signal causes an increas in the voltage returned by the
sensor, so the ECU does not believe the throttle plate is fully closed, and tries
to continually adjust the ignition timing and fuel injectors to for a condition
it can't determine is idel or above idle.
If you insist upon this hunt-and pray method, your possibilities are: coolant
temperature sensor, mass air pressure sensor, intake air temperature sensor
(thermistor), oxygen sensor (exhaust), etc. You should disconnect the
battery for several minutes after making any changes to clear the learning
portion of the computer memory, this way, if you are lucky enough to guess
which sensor is bad and replace it, the computer will not continue to try
to compensate for the bad sensor that it sensed before.
If you decide to take the vehicle to a service department to have it scanned,
make sure that they have and can opperate a Delco Tech I tool and have the
software to service your vehicle. Know that these Delco computers (ECU or
CPU as they may call it) are flash programmed. They do not have a static
programmed prom chip, and rather are "flash programmed" by loading with the
software from the Tech I while the computer is installed in the car. They
do have learning modes, do have a memory, and are programmable. You will
find that many dealer service departments have little or no experience
working on anything other than trucks and sport utility vehicles. They
may have no experience in dealing with the Delco based computer controls
on these vehicles, and may even make claims that these computers are not
programmable, etc. Make sure that you quiz the people who you intend to
have service your vehicle. If they are not familiar with the Delco based
computers, claim anything other than that they are fully programmable and
flash programmed using a Tech I, or indicate that they lack the hardware
and software to service your vehicle, do yourself a favor and take your
vehicle somewhere else to someone who has at least the slightest idea of
what they are doing.
Also note, that there have been numerous recalls on the Delco ECUs used
in the Isuzu and Storm models which are listed at the
Alldata website. Specifically,
all 1991 Isuzu cars have a standing recall # 9101001 under General
Recalls for a ECM replacement campaign, and all 1990-91 Geo Storms have
a standing recall # 91C066E under Emissions Recalls for ECM replacement
because of emissions non-compliance.
It appears that the computers should be recalled,
and that a recall was issued by Isuzu, but that this recall is no longer
being honored by the company. If this is the case with your vehicle,
changing all the sensors will have no effect, and only by replacing the
ECU will you ever solve the problem.
Lastly, to improve drivability without fixing the problem so that you
can use the car despite its idle problem, if you find that the vehicle
is revving and dropping and trying to die, you may wish to try one of
the following temporary cures:
If you live in a climate with little temperature variation and it is
always 70 degrees Farenheight or above, you may wish to start the
engine, allow it to warm up, wait for the engine to idle at a normal
speed, and then simply un plug the IAC solenoid. This disables the
IAC solenoid and the computer will not be able to continually try to
correct for whatever problem it has that is serious enough to warrant
correction, but not serious enough to bring up a trouble code when the
codes are run. Disconnecting the IAC solenoid will, however, make it
almost impossible to use the air conditioning, as the IAC solenoid
usually adjusts the idle speed up to compensate for the increased drag
of the compressor. Disabling the IAC solenoid eliminates this, and the
engine will die if you turn on the air conditioning. This will also
happen if the temperature drops enough, and engine warmup will become
difficult.
Adjusting the throttle plate stop on the throttle body is the second
possible action, which works much better if you are in a climate where
the temperature is not steady and cooler whether is normal. Note that
the throttle stop is set at the factory, there are no instructions to
return the throttle stop to its original position, and if you have the
vehicle serviced by a dealership service department, their instructions
are to replace your throttle body ($400.00 or more) if the adjustment screw
has been tampered with. That said, you can adjust the idle screw in several
threads to artificially raise the minimum idle speed. The computer will
still try to compensate, but will not be allowed to let the engine speed
drop low enough to kill the engine. The side effect will be that once the
engine gets hot, the idle speed will hover between 2,000 and 3,000 RPM often
when you pull to a stop at a stop light or stop sign. Some times it will
work its way down after several minutes, and sometimes it will simply hover
at that point. It is annoying, but much less so than having to continually
restart the engine every time you come to a stop. This temporary solution
should not be used in the long term. It is not good for the engine to run
above idle for long periods with no load. In addition, it is not good for
the life of the clutch to start from a standing stop at 2,000-3,000 RPM
all the time.
Sticking Throttle:
Sticking throttle is another common problem among Isuzu engines. This is
most commonly seen when pulling off the highway or to a stop light or
sign after cruising at a steady speed for a while. You probably find
yourself tapping the throttle every time you come to a light to kick the
idle down.
You should first make sure that this is not the Idle Solenoid sticking or
causing problems. Plug the vacume hoses that it feeds from in the
induction pipe and intake manifold and make sure that the problem
persists, this will eliminate the idle solenoid as a possibility.
When the throttle sticks, pull off the road, pop the hood, and attempt to
manually push the linkage into the closed position. If the linkage
moves, and the idle speed decreases to normal, you have found your
problem.
First make sure that the linkage does not have
too much slack and sloppiness in the cable is not causing the problem.
Also check to make sure that there is enough slack in the throttle cable
to allow the linkage to return to a resting position.
After eliminating these possibilities, try the following:
Remove the throttle cable and housing. Isuzu cables and housings are
noted for wearing poorly and sticking. Use white lithium grease from a
tub and white lithium aerosol spray grease and work the two into the
cable housing by hanging the cable feeding the thick and thin greases
into the housing and vigorously moving the housing back and forth over
the cable to get the grease evenly spread within the housing. Reinstall
the cable.
There is also the possibility that the throttle plate (butterfly) is
sticking within the housing. To cure this, after thoroughly greasing the
cable, get a very stiff spring from your local hardware store and install
it in place of your OEM throttle return spring. Do not use the
cruise control while you have a heavy throttle return spring
installed. The throttle should feel like a heavy clutch pedal.
Drive around for several days with the heavy spring on. Be careful that
the heavy gas pedal effort doesn't get you into a hazardous situation.
After several days, the plates should have seated themselves better and
should return to their propper resting position.
Idle Adjustment Screw Cleaning; For G200, 4ZC1, and 4ZD1 Engines:
Isuzu engines seem to pull some of oil through the crank case ventilation
system when they are run hard. This oil is pulled into the intake piping
and thrown onto the throttle body, where it gums up on the end of the idle
adjustment screw. It is easy to clean by removing the screw and
cleaning it with Gumout, cleaning the shaft with
Gumout and a pipe cleaner, and spraying Gumout through the air
passage way at the inlet of the throttle body.
EGR Passage Clogging:
In a similar manner as described concerning the idle adjustment screw and
its tendency to clogg, so to does carbon and gunk build up in the small
passage that leads from the EGR valve at the rear of the air
plenum/common chamber to the throttle body inlet. Removing the EGR valve
and spraying Gumout through the passage will clean the passage out.
Spark Plug Cleaning Made Easy:
Spark plugs foul no matter how fancy, expensive, or well designed. Sand
paper won't get in all the spaces that need to be cleaned, and both sand
paper and sand blaster attachments leave a rough texture on the metal of the
plug that just invites more fouling and buildup. An easy
solution that involves less work can be found on the shelf
of your local discount store. The product is called CLR and is
sold in the household cleaning section of many
stores. The product is designed to remove calcium, lime, and
rust (CLR) from metal surfaces, and it works
remarkably well on fouled plugs. Simply pour a half inch of
CLR into a small narrow disposable plastic cup and
stand the fouled ends of the plugs in the liquid for an hour
or two. Then remove the plugs from the liquid and use
an old tooth brush to remove the debris from the plug. Rinse
them with water, allow to dry, and reinstall them.
Battery Terminals:
Battery terminals corrode, this is a fact of life. On fuel injected
vehicles, this corrosion can cause problems with the computer system.
Dirty terminals will allow enough current past to run acessories
(headlights) but may not allow enough current to start the vehicle.
Periodically clean the posts and terminals with fine steel wool, but be
sure that the connectors are well apart, running 12 volts
through steel wool will start it on fire. Consider gold
plated car audio type terminals, they corrode less. Also
consider replacing your primary wires with a better
quality, higher guage cable, this will make starting the
engine much easier as well as enable better current flow.
Cam Installation:
The chain tension release on G200Z engines is tricky. You may have to
turn the release several times to fully detension the chain and get
enough slack to align the cam.
Never try to turn the cam by applying pressure or twisting on the cam
alignment post. This post is only pressed into a hole and is very
delicate. It will break easily if you are not careful and another cam is
quite expensive.
Ram Air Induction for Non-turbo Impulse and Piazza JR:
The cold air pick up pipe on the G200Z and 4ZD1 equipped Impulse JR
models is taylor made for ram air conversion, and all the parts needed
for this conversion are readily available at your local hardware store, and
are cheap. You will need a piece of 4 inch diameter PVC pipe, a
4 inch diameter rubber right angle elbow, a 4
inch diameter PVC test plug, a peice of welded wire cloth, four
five inch diameter hose clamps, and some 3/4 X
3/16 or similar size aluminum bar stock. First, remove the
stock cold air induction pipe from the filter box and
mounting clamps. Cut the a 23 inch length of PVC pipe. Put the
rubber elbow fitting onto the end of the air box
inlet and slide the PVC pipe into the open end of the rubber
elbow so that the new assembly runs across the
front of the radiator and behind the grill, just as the
original did. Now mark the pipe at the point that the frame
uprights flank each end of the grill opening, this will be the
marks for the ends of the slot that you will cut for the
air to go through. Cut a slot in the side of the PVC pipe
approximately 15 inches long and 2 3/4 inches wide,
down the length of the pipe, with the ends at your marks. You
will need to use a cutting disk, either on a drill or a
dremmel, to cut the slot, and use a rotarry rasp to dress the
edges. Now, cap the open end of the pipe with the
test plug, you may need to glue it in if it is not snug
already. Cut a piece of wire cloth to fit over the slot and
protect it from large debris. Use two of the hose clamps, one
at each end, to firmly attach the wire cloth cover.
Reassemble the rubber elbow and the pipe on the car as you did
before. Now cut two pieces of the aluminum
bar stock and bend them around the pipe, following the pattern
of the clamps that held the original pipe in place.
Trim the ends down and drill mounting holes. Clamp the ends of
the rubber hose at the air box and at the PVC
pipe and clamp the pipe into place with the newly fassioned
clamps, with the slot positioned so that it faces
forward toward the open grille. You're done. Remove it and
paint it black if you like.
Remember: Youre air filter WILL get dirty faster, and you will need to
clean it more often. If you drive in an area with lots of bugs, you will
later find them embedded in your filter.
At highway speed, this ram air intake will force five times the engines
more air than the engine needs. This will cause a respectable level of
pressure in the intake system. Be sure that all of your vacume hoses are
in good shape and well attached. If you coast with the clutch in at
highway speed, you will notice that the ram air
assembly will raise your engines idle speed by 500 or more RPM.
Fuel Leaks Around the Fuel Rail:
On the Impulse/Piazza JR, prior to the 1988 model year, the fuel
injectors are attached to the fuel rail with a piece of rubber fuel hose.
The hose is clamped to the fuel rail, but, the hose fits into the
injector on a barbed hose fitting with a round (often blue)
"slide-in-clamp" type fitting. These really don't work all that well,
and this is where you are most likely to find leaks, especially if you
raise the fuel pressure or remove the injectors from the
rail in the process of servicing them or another part of the
intake or engine. It is a simple matter of installing a
worm gear clamp to each hose at the base of the injector over
the area where the barbed pipe is beneath the
hose. You don't even have to take the injectors away from the
rail if you back the worm clamp al the way out and re-assemble it around
the hose.
Oil Loss On Isuzu Engines:
You are loosing oil, but can't find any leaks or spots on the ground and
the exhaust is only giving a bluish puff of smoke when the engine is
started after sitting a while. You are most likely experiencing a case
of bad valve guides. Isuzu engines have a reputation of being very durable,
with the exception of the valve guides, which are
known to go bad quite frequently.
Electical Gremlins:
If you are having problems starting or restarting the vehicle or having the
ignition cut out while driving, before you begin rewiring or replacing starters,
batteries, or the ignition system, do some routine maintenance to make sure
that something simple isn't causing your problem.
Check to make sure your battery terminals are tightenned on the battery posts.
This is especially important if you have just received the car mack from having
it serviced at a shop. Shops routinely remove the battery posts while servicing
a vehicle to avoid safety hazards. They sometimes forget to tighten down the
terminals and if they are loose, they will sometimes loose contact and cause the
engine to stop temporarily. This will also cause starting problems. There may
be a adequate connection to light the dome light and run the radio, but a loose
terminal may not allow enough electicity to pass to start the engine.
Check your battery terminals for corrosion or oxidation. Clean and polish both
the battery posts and the terminal clamps. Neglected terminal connections is a
very common cause of electrical dificulties. You may even want to use those
little battery post donuts, they do work to reduce fouling of the connection.
Check to make sure the battery has enough and not too much water in it.
Underfilled water will result in a battery that will not hold a charge.
Overfilling the battery with water will cause the battery to boil over while
the car is running and this will significantly add to the previous discussed
corrosion problem as well as rust around the battery.
On gel cel and sealed batteries, check for damage and splitting of the case.
Overcharging can cause these batteries to crack, and they will then not hold
a charge.
Check the primary wires for oxidized or corroded grounds and connections at
the terminals, grounds, and the starter. Fouled electrical connections will
not allow electrical current to pass.
Manifold and Down Pipe Cracking:
On the FWD models, manifold and down pipe cracking can be a persistent problem.
Vertical cracks in the cast iron manifold are the result of metal fatigue caused by
the fact that the aluminum engine head and the cast iron exhaust manifold expand and
contract at different rates when heated and cooled. In addition, cast iron manifolds
tend to shrink over time from this heating and cooling and this will cause cracking
as well. The only solution to this is to replace the manifold with a redesigned
aftermarket manifold that has a full flange across the mounting surface or to use
an exhaust header.
Horizontal cracks in the cast iron manifold or in the weld joints of the down pipe
indicate that the engine mounts and/or torque bar are worn out or damaged. If these
mounts are not securely holding the engine, the engine will twist freely and the
exhaust system will be the only thing to resist this twisting. As a result, the
engine will tear the exhaust system to pieces. The solution is to repair or replace
the engine mounts and/or torque bar. If a manifold or exhaust pipe showing damage
caused by bad engine mounts is replaced and the engine mounts are not replaced, the
damage will reoccur.
False Driveshaft and Axle Balance Problems in Impulse RS AWD:
Numerous owners have complained about the balance of the axles and
driveshafts of the AWD Impulse Turbo, defining the symptom of this as a shimmy
and shake from the rear of the car whenever the car is driven over 30-40 MPH.
New axles and driveshafts, rebuilt axles and driveshafts, nothing seems to help.
This problem seems to be rooted in the OWM wheels. The six spoke, aluminum,
15x6 stock wheels have very thin inner structure. I have never seen one that
was not bent on the inner lip. A bent wheel will cause a shake in any vehicle
driven above 30-40 MPH, and it just so happens that all of the wheels originally
installed on the AWD cars are of such slight structure that they are bent.
The solution is to install new wheels, preferably anything but OEM 15x6 Impulse
RS AWD wheels.
Selecting the correct tire size for Plus size wheels
The first thing to understand when considering tire sizes is that the
"Series" as in 60 Series, 50 Series, etc. is not a measurement of
the sidewall height in the same way that the width measurement is the size
of the tread width. The "Series" measurement is a ratio of the sidewall
height in relation to the tread width. So a 195/60 14 does not have the
same sidewall height as a 205/60 14 because the width is not the same,
therefore, the sidewall which is in direct relation to the tread width
measurement. This "Series" ratio is one of the most confusing things
about tires, don't ask why they made their measurements this way, they
would have been best off with a direct sidewall measurement, but that's
not what they did.
When selecting a tire size for either a wider tire on your OEM wheels or
for a larger wheel size, it is important to maintain as close to the OEM
tire diameter as possible if you have any intention of keeping your
speedometer accurate. Two percent is generally considered within
reasonable variation, but the lower the variation the better. It is best
to use one of the many wheel and
tire calculators on the internet. Changes in wheel widths will account
for some minor variations, but the following are general guidelines
based on the several wheel calculators:
For 1983-89 Impulse/Piazza JR
Speedometer calibrated for 195/60 14:
Wheel Diameter Tire Size Percent Error
14 Inch 195/60 14 0
205/60 14 + 2.035
205/55 14 - 1.442
215/55 14 + 0.424
235/50 14 - 0.160
15 Inch 195/55 15 + 1.001
205/50 15 - 0.611
215/50 15 + 1.085
225/45 15 - 1.035
235/45 15 + 0.492
245/45 15 + 2.018
16 Inch 195/50 16 + 2.001
195/45 16 - 1.306
205/45 16 + 0.220
215/45 16 + 1.747
215/40 16 - 1.900
225/40 16 - 0.543
235/40 16 + 0.814
245/40 16 + 2.171
17 Inch 205/40 17 + 1.052
225/35 17 + 0.050
235/35 17 + 1.136
I would recommend against any tire wider than 215 mm because everyone who
has tried 225 mm or wider has complained about problems with the tire
rubbing the fender lip and frame.
For 1985-89 I-Mark/Spectrum/Gemini JT/RB
Speedometer calibrated for 175/70 13:
Wheel Diameter Tire Size Percent Error
13 Inch 175/70 13 0
185/65 13 - 0.782
205/60 13 - 0.170
225/55 13 - 0.430
14 Inch 185/60 14 + 0.417
195/55 14 + 0.887
205/55 14 + 0.026
215/50 14 + 0.800
245/45 14 - 0.150
15 Inch 185/55 15 + 1.617
185/55 15 - 1.599
195/50 15 + 0.139
205/50 15 + 1.878
205/45 15 - 1.686
215/45 15 - 0.122
225/45 15 + 1.443
245/40 15 - 0.310
16 Inch 185/45 16 - 0.400
195/45 16 + 1.165
205/40 16 - 0.834
215/40 16 + 0.556
225/40 16 + 1.947
245/35 16 - 0.460
17 Inch 175/40 17 + 0.590
205/35 17 - 0.010
235/30 17 + 0.410
For 1990-93 Impulse/Piazza JI, Stylus/Gemini JS, Geo Storm/Gemini
Coupe
Kip Anderson has stated that 225 width tires will not fit on the back of
the Impulse JI without a shallower wheel offset and fender flares.
Speedometer calibrated for 185/60 14:
Wheel Diameter Tire Size Percent Error
14 Inch 185/60 14 0
195/60 14 + 2.078
195/55 14 - 1.298
205/55 14 + 0.606
245/45 14 + 0.260
15 Inch 185/55 15 + 1.195
185/50 15 - 2.008
195/50 15 - 0.277
205/50 15 + 1.454
205/45 15 - 2.095
214/45 15 - 0.537
225/45 15 + 1.021
245/40 15 + 0.100
16 Inch 185/45 16 - 0.814
195/45 16 + 0.744
205/40 16 - 1.247
215/40 16 + 0.139
225/40 16 + 1.524
245/35 16 - 0.050
17 Inch 185/40 17 - 0.370
205/35 17 + 0.390
245/30 17 - 0.200
Wheel Bolt Pattern and Hubcentric Ring
The bolt pattern of Isuzu car and Storm wheels is the same whether you are dealing
with a FWD, AWD, or RWD model.
4 x 100 mm is the bolt pattern. Lug bolts are 12 mm x 1.5 thread pitch.
The hubcentric ring in the center of the lug bolts of the 1985-89 I-Mark and
Geo Spectrum, 1990-93 Impulse, Stylus, Geo Storm, and Asuna Sunfire is 56.5 mm
which is somewhat uncommon. This becomes a problem in finding wheels for these cars.
Aftermarket wheels are typically made with large hubcentric ring size of something like
74 mm and then use ring inserts made of plastic or aluminum to adapt the same wheel to
numerous hubcentric ring sizes. Unfortunately, 56.5 mm adaptor rings are totally
unavailable from any source. Wheels can be ordered by specification with a 56 mm ring
(relatively common) insert and the center bore of the insert can be enlarged using a
sanding drum on a drill to ever so slightly enlarge the 56 mm center bore to 56.5 mm
to fit the hubs of these cars.
The hubcentric ring in the center of the lug bolts on the 1983-89 Impulse JR is 57.1 mm
in diameter. This size is relatively uncommon and this can be a serious
problem if you are trying to fit a wheel intended for another model vehicle onto an
Impulse JR. The only other wheel sharing the 4 x 100 mm bolt pattern with the
57.1 mm hubcentric ring is Audi. Wheels intended for a smaller hubcentric ring than
57.1 mm can be bored out and made to fit the Impulse JR. Wheels intended
for a larger hubcentric ring can be adapted with a donut like ring insert available
from many aftermarket wheel companies. Most aftermarket wheels have very large center
bores and are meant to be used with these hubcentric rings so that they can be adapted
to a wide variety of applications.
This can become a very difficult issue when trying to find hub adaptors so that you can
use the deeper FWD offset wheels (35-48 mm) in place of the shallower offset wheels of
the Impulse JR (24 mm).
Wheel Offsets
Wheel offsets become pretty tricky when you are using plus one, plus two, and
plus three wheel applications. The difference between correct and incorrect
wheel ofset will determine if your tires rub the fender lip on bumps or the
frame on turns. This is important for safety as well as tire wear. Extreme
lowering will make this even more difficult.
1983-89 Impulse and Piazza JR
The stock offset for the JR is 24 mm with the stock 14x6 alloy wheel and 195/60-14
or 205/60-14 tire.
The JR has plenty of space in the wheel well and there is a bit more flexibility
with this one than most, though it is almost impossible to find any variety of
wheels with an offset in the area of 24 mm. This offset is common only to the
1980's BMW 3 Series, Opel Kadette, Opel GT, Opel Manta, and the 1980-84 Isuzu
I-Mark. Wheel adaptors (hub adaptors) and spacers can be used to adapt the vehicle
to use FWD offset wheels and this will allow for a much wider selection of wheel
styles.
Using wheels up to 7 1/2 inches in width with the same 24 mm OEM offset will
work quite well.
Most of the English Piazza owners are going to a 20 mm offset to space the wheel
slightly closer to the fender line for a beefier appearance, and they have noted
no clearance problems even while lowering the car as much as 2 inches.
1985-89 I-Mark and Gemini JT
The stock offset for the JT is 49 mm with the stock 13x4.5 steel and 155/80-13 or
13x5 alloy wheel and 175/70-13 tire, or 46 mm with the stock 14x5 alloy wheel and
185/60-14 tire.
The JT is typical of the FWD cars and is pretty tight for space in the front wheel wells.
Clearance is tight on both the inward side at the frame on turning as well as with the
strut body and on the outward side between the tire and the fender lip. Excessive
lowering becomes a real problem with wider wheels and tires on these models, though
there should be little problem with the correct offset and up to 1 3/4 to 2 inches
of lowering.
Momo/Konig recomends a 35-38 mm offset for all wheel sizes. Note that this may be an error
in their database.
1990-93 Impulse, Piazza, Stylus, Gemini, Storm, Gemini Coupe, and Asuna Sunfire
The stock offset for the 90-93 models varies based on model and trim level from 40 mm
with the stock 14x5 steel or alloy wheel and a 185/60-14 tire to 40 mm with the
stock 15x6 alloy wheel and a 205/50-15 tire.
The 90-93 models are typical of the FWD cars and is pretty tight for space in the
front wheel wells. Clearance is tight on both the inward side at the frame on
turning as well as with the strut body and on the outward side between the tire and
the fender lip. Excessive lowering becomes a real problem with wider wheels and
tires on these models, though there should be little problem with the correct offset
and up to 1 3/4 to 2 inches of lowering.
Momo/Konig recomends a 35-38 mm offset for 14x7 to 16x7 wheels. They recomend a 35-42 mm
offset for 16x7.5 to 17x7.5 wheels.
Mike Robinson has noted that he has some rubbing problems with his 35 mm offset on
15x6.5 wheels on his Stylus which is lowered about three inches. He has had rubbing
on the inward side at the frame on the front when cornering and on the outward side
on the rear, and commented that he has solved most of the problem by rolling the
rear fender lip for more clearance on the outward side.
Wheel Weights
How much a wheel and tire weigh are important to the performance of a car and must be
considered when looking at aftermarket wheels. Ever notice that no one ever bolts on
16 and 17 inch wheels to race on in the pits at the drag strip? Ever notice that all
the racing compound tires for autocross and road racing are 50 series and for 15 inch
wheels? This is because racers and racing tire and wheel manufacturers know that
larger wheels and lower profile tires weigh more, and forcing the car to turn heavier
wheels and tires eats up valuable power that could be used to move the car across the
pavement. In short, lighter wheels and tires will free up more power for things like
acceleration.
The overall weight is not the only concern, because even larger diameter wheels and
tires that weigh exactly the same as their smaller diameter counterparts will loose
some power due to the fact that the structure of the wheel and tire is moved farther
from the axis of rotation requiring more effort by the engine and drivetrain to spin
them.
Sport Compact Car and Turbo (McMullen Argus Publications) reported dyno testing of a
car with stock wheels and tires weighing 29 pounds compared to larger diameter wheels
and with lower profile tires weighing 38.5 pounds. Their results showed a 3.8 HP loss
due to the added weight. This amounts to .4 HP lost for each additional pound of
wheel and tire weight.
The overall theme is that bigger is not always better. Larger diameter wheels and
lower profile tires do significantly better in cornering, because they flex less and
stick better, but this is all at the expense of acceleration ability, and most of us
want to accelerate out of curves and turns. These two must be considered, and it may
very well be that a 15x7 theel and a sticky 205-50-15 tire will do much better for
your application than a big, heavy wheel that serves more for appearance than for
performance.
Something else to keep in mind with extremely light weight and racing wheels, they are
often not as strong as regular road wheels. Racing wheels are meant for use at the track,
where there are no speed bumps, railroad tracks, pot holes, and curbs.
Wheel Model Weight Tire Weight Combined Weight
90-93 Impulse/Stylus/ 16 lbs 16 lbs (195-60-14) 32 lbs
Storm, Steel, 14x5.5
90-93 Impulse/Stylus/ 14 lbs 16 lbs (195-60-14) 29 lbs
Storm, Alloy, 14x5.5
90-93 Impulse/Stylus/ 16 lbs 18 lbs (205-50-15) 34 lbs
Storm, Alloy, 15x6
Typical Aftermarket 15-21 lbs 19 lbs (205-45-16) 34-40 lbs
16x7
Typical Aftermarket 18-27 lbs 20 lbs (205-40-17) 38-47 lbs
17x7
Bogart 15x7 10 lbs 14 lbs (Drag Slick) 24 lbs
(Drag Racing Only)
SSR Competition 15x7 9.9 lbs 14 lbs (Drag slick) 23.9 lbs
Volk TE37 15x7 9.2 lbs 14 lbs (Drag slick) 23.2 lbs
Kosei K1 15x7 13.5 lbs 18 lbs (205-50-15) 31.5 lbs
Racing Hart 17x7 13.5 lbs 20 lbs (205-40-17) 33.5 lbs
Nippon Racing 17x7 14 lbs 20 lbs (205-40-17) 34 lbs
Critiques of Tire Brands and Models
Keep in mind that some tires work well on some models of cars and not so
well on other models of cars. This is particularly applicable in that
some tires work well on RWD cars while not working as well on FWD cars and vice versa.
BF Goodwrench
"I have a set of the Euro T/As and I definately do NOT recommend them. The
sidewall is way too mushy to be driving on, and the grip is so-so at best."
Jason Silverberg
"I've got BFG Comp TAs (205/50-15s) on my Impulse RS. Treadware has been
great, performance, wet and dry, as good as the dealer said -- which is to
say a notch lower than a super-sticky, short-life, full-performance tire.
Got mine mounted, installed, balanced, etc. for about $350." Zeke Ulrey
"I have BF Goodrich touring HR4 on my
Stylus and like them too. They have a stiff sidewall and you feel every bump,
and corner well. They are not worth much when the road is wet however."
Michael
"I have BF Goodrich Comp T/A ZR's on my sunfire, and damn do i
love them, rides a bit rough but the handling benefits are totally
worth the extra cost." "I would highly reccomend the BF Goodrich Comp
T/A ZRs, I have a
set on my car and wow do they stick, tread wear is reasonable for
such a tire and they are excellent in the wet. however once
conditions get any worse than rain, my car stays in the garage.
BFG also has a Comp T/A HR4 that might be a bit better than the
ZRs in the snow. My car came with the Comp T/As but i don't
believe they're too insanely expensive, but performance has its
price." Dave Grant
"I like the BF Goodrich TA radials (205-50-15) They are cheap ($80 per) and
seem to handle well. Plus they are a good 1/2" wider than any other 205-50-15
I've seen." Michael Kuriger
Bridgestone
"I have a set of Bridgestone Protenza RE900s and I love them! I'm getting ready
to get another set, these are a little wore. They are pretty sticky, but don't
seem to wear out too fast under normal driving. I have tried everything on
these tires and they have never squealed in a turn. I was coming home from
work one day and took my favorite turn (around 80 degrees or so) at 65 mph,
the car floated a little before it grabbed, bottomed out my Intrax springs,
but the tires only hummed a little and I think that was them rubbing the wheel
well. So I would definitely suggest these tires to anyone. They aren't priced
to bad either, around 90US bucks." Brad Blickenstaff
"I just bought the Bridgestone RE910s, and they are a
world of difference!! First, they have a very good looking sidewall with
a rim guard and a modern tread design. That's on first impression. Once
on the car though, it gets better. They are smooth, quiet, have low
impact harshness, and great turn in. We've had a mix of snow and rain in
Toronto, and I've been impressed, It's only been a couple of days, but
with a treadware rating of 400, hopefully this impression lasts a while!"
"I recently put a set of RE910's on my '91 RS and I've been more than
happy with them. They have excellent wet and dry (and snow!) grip and
have a UTQ rating of 400. Not only that, but they offer a rim protector
guard, which is unusual in this price range. Overall, I've found them to
offer tremendous value." Nader Gorgi
"i'm happy with the 205/50-15 Bridgestone Potenza RE910
on my '91 RS. they're T-rated, 400-tread/A-traction/B-temp.
don't go over 32 psi on the rear--i've been running 35F/30R." David Chanin
Dunlop
"previously forced, due to money considerations, to buy Dunlop GT
Qualifiers (and hating them!)". Chris Rhoades
"Dunlop SP 8000 are impressive on my dad's supercharged Miata, letting him
accelerate quite briskly in rain without spinning." Troy Hockerman
"I purchased a set of Dunlop D60A2 JLBs from Discount Tire Direct last
September. They are all season performance tires with a 300+ treadware
rating. A helluva lot better than the Good Year GT+4s that I had. A
lot cheaper,too! $53 a pop! Got them installed and balanced for
another $10 each. They ride extremely well in rain and light snow. I
haven't hydroplaned and haI haven't gotten stuck at all last winter.
They also seem a bit stiffer than the GY GT+4s." Victor Dumeng
"I just bought the Bridgestones, and they are a
world of difference!! First, they have a very good looking sidewall with
a rim guard and a modern tread design. That's on first impression. Once
on the car though, it gets better. They are smooth, quiet, have low
impact harshness, and great turn in. We've had a mix of snow and rain in
Toronto, and I've been impressed, It's only been a couple of days, but
with a treadware rating of 400, hopefully this impression lasts a while!"
Kerry Chin
"I have D60A2 JLB's on my 89 JR and the handling was
superb compared to the GT+4's that I had. Handling on snow was improved
dramatically! With the GT+4's the car would not stay still on a straight
away with snow. I had to drive very slowly to keep from moving the steering
wheel so much. With the JLB's, the car barely moved astray and I could dive
a bit faster. I highly recommend them , especially with their 350+
treadware!!
Oh, and yeah, to get them to squeal, I took a turn at around 45mph where
the GT+4's would be squealing at 30mph!! TO think I paid $117 for each GT+4
when I paid $55 for each JLB's!!" Victor Dumeng
Falken
"If anyone needs/wants a tire that handles superbly in the rain, look at the
Falken Ziex. They have a deep track down the center that's like the Goodyear
Aquatread. Never have I felt so secure diving thru a puddle at 60 MPH as I do now.
Plus they have a good treadwear rating (400, I think) but don't have that
'Handling By Mattel' feel to them." Chris Rhodes
Firestone
"I have Firestone Firehawk SVX v-rated 205/50 r15s. They seem better in the
rain than my original RE-93s. The RE-93s would tend to "saturate" with water
on the roadway and feel real heavy to steer. The SVX's seem great all the
time." Vince Vonada
Goodyear
"I have used the Goodyear Eagle ST tires on my 86 Impulse, and found that
they wear quickly, grip average on dry surfaces, and are almost totally helpless
on a wet surface or snow. In addition, they would not last for more than 20,000
miles. I would not recomend them to anyone." Bill Luton
"...my .02 on Goodyear tires: stay away. I used to work at a Goodyear,
and from what I saw working there, they all cup, no matter what. Better
much better tires can be had for lots less." Troy Hockerman
Lee
"My tire of choice is Lee Turbo Action. Laugh if you must but these tires are
tough as nails. (had them bend a few without taking damage.LOL) Handling is
moderate but I'm also still running the 185-60-14, they do like rain, no
problem with snow or ice (Flagstaff had 2 or 3" of ice that year very hard to
walk on if your not use to it) , and they'll do off road quite nice. Phoenix
always has the roads torn up plenty of chances to shred tires." T. Y. Bear
Nito
"My friend has some Nittos and they're sticky as hell.. Great tires, but
wear out quite easily (especially if you do the e-brake and sliding
action). They aren't very well though for wet surfaces.quot; John Syko
Toyo
"I just last week had a set or Toyo FZ4's put on my Asuna and these are the
best tires I have had so far. I have tried the Yokohama’s but the tread
compound was really soft and the tires only lasted 8 months. The Comp T/A's
are good but trust me you will feel every bump in the road. So far the
Toyo's have been great V groove so they are great in the wet, but the only
bad thing is that due to the tread pattern they pick up a lot of stones.
The shop were I had them installed gave me 30 days to see what I think but
for the money I will be keeping them." Simon Matthews
"I just replaced a set of Yokohama AVS-Intermediates (15") with Toyo FZ-4's
(16") on my '91 Impulse XS and I completely agree. It's not really a fair
comparison because the Toyo's are 205-45 VR16 and the Yoki's were a
well-worn 205-50 ZR15.
Regardless, I'm really impressed with the Toyo's. They're quiet, ride well
and absolutely fantastic in rain. The Yoki's seemed a little happier near
the limits of traction and were crisp and responsive on the ragged edge.
The Toyo's get sort of 'greasy' feeling just before they let go. More
warning than the Yoki's, but this only seems to really matter on those
cloverleaf-off-ramp-skidpad-thingies, anyway. In normal spirited driving,
the FZ-4's are really responsive and provide great feedback." William Wilson
"I am currently running FZ4`s (toyo) on my RS. they are my second set and i
really like them, for an all season tire they offer very high preformance
for the money, Being a AWD i cant see spending more on summer tires, IMHO.
Mind you, that is also on stock rims. 112$ CAN each." Fraser Cassells
"I bought a set of Yokohama S306 for my 1989 Impulse Turbo. A couple miles
later, I realize that these balloons I am driving on are definitely not
performance-oriented. They stick pretty well, but the turn-in feels so soft and
mushy." Soren Rounds
"I purchased the S306's against my will, too. My car
squeals over the silliest of turns now. They don't feel unsafe, just
noisy. And I get looks from people, like I'm some kind of maniac." Vijay Gidad
"I only use Toyo tires, 800 plus for I-Mark, T-1 Proxie for Impulse RS. I
could not be happier." "I have Toyo Proxes T1 Plus and find them excellent. I did not want all
season tire. Dave Batson" Dave Batson
"I haven't really pushed the T-1's on my car yet, but they've had excellent
wear and seem to stick pretty well. No problems in the rain with them either."
Mike Robinson
Yokohama
"I have used the Yokahama A 378 tires on my 1986 Impulse, and believe that
for this particular vehicle, they are the best touring type tire available.
Grip is good on all surfaces, wet, dry, or snow. Wet traction is superior to
anything I've seen in any tire available. Wear life is exceptional, lasting
30,000 miles and longer. I also tried these tires on my 1991 Stylus, and found
that they are not suited well for the front wheel drive layout. Traction on
dry and wet for the drive wheels is not very good. Cornering traction and tread
life continue to be high points, but for for starting from a stop, these are not
a very good choice for a FWD car." Bill Luton
"I have been abusing Yokohama A509s on my 89 Impulse for a while now.
Treadwear is not too good, I am in need of new tires already (about 13,000
miles). They gripped very well wet and dry when new. They still work well
on dry pavement even though they are almost bald now. I will probably buy
the A509 again when it starts raining here in the fall." Soren Rounds
"My brother and I both have a set of Yokohama A520's which are working quite
well." Troy Hockerman
"I'm running Yoko 520s (205/45-16) and I've been 4000
miles on them now. They grip ok, except in the wet when you go into a slide
without enough notice. In the dry they are quite grippy though. Problem is,
they come with 8mm tread and I'm down to 6mm on the back and 5mm
on the front already. That means less than 10,000 miles for a set of tyres."
John Appleby
"I splurged for Yoko AVSi Intermediates
and absolutely LOVE them. If I could afford it, I would get them again in a
heartbeat!" Jason Silverberg
Front Brake Disc Transplant for 1985-1989 Gemini JT, RB and I-Mark
JT:
Overseas, front brake discs for these vehicles can be hard to find and
expensive. Haken Hedgren
indicated that the front brake discs from a 1985 Toyota
Starlet are both more economical and more plentiful, and with a little
bit of modification, will go straight on. The Starlet has ventilated
front brakes which are 16 mm thick, 226 mm in diam. 140 mm center hub,
and total thickness (disc+hub) 45mm. Simply enlarge the center hole
to 57 mm and drill new 12.2 mm holes for the lug bolts to go through, and
as long as the brake disc doesn't doesn't rub the brake hose, your
transplant is successful.
Front Brake Disc Transplant for 1990-1993 Storm and Stylus Base Models:
12 Valve Storm and Stylus models have 9.06 inch diameter front brake rotors
while the GSi and XS models of these vehicles have 9.76 inch diameter front
brake rotors. Swapping up to the larger size is a simple matter of installing
the larger rotors and calipers to accompany them.
Brake Squeal
Brake squeal is very common in all Japanese cars, and Isuzus are no
exception to this. Given that the squeal is not due to the feelers
rubbing and telling you to buy new pads, squealing is caused by the pads
vibrating between the caliper and the rotor.
Auto parts stores sell "stop squeak" aerosol spray which is an
adhesive that you spray onto the back of the pad before installing it in
the caliper. I have found that this product works about as far as the
end of the block, and then squeaking begins again. It does not seem to
last very long anywhere that you find yourself driving in the rain very
often. In addition, the parts of the pad that it does stick to, the
adhesive picks ip lots of rocks and dirt, and it is not overly easy to
remove if you need to remove and reinstall the brake pads.
I have found another method that works better, but does not eliminate
squeal altogether. Use Permatex RTV Form-A-Gasket, Copper High Temp, to
adhere the pads to the calipers. Dab a little bit on the backs of the
pads where they rest against the caliper and install them while the
form-a-gasket is still wet. This will hold the pad, but not with a death
grip, so don't worry, you will have no problem removing them. In
addition, the form-a-gasket is rubbery and keeps the pad and caliper from
vibrating against each other. In addition, it raises the overall mass of
the pad and lowers the resonance, reducing the pitch and outpu tof the
sound from vibration.
Coil Spring Replacement for Impulse and Piazza JR:
The front coil springs on the Impulse JR require a special tool for
removal and installation. They DO NOT use a standard, generic
spring compressor as most vehicles but require a specific tool
that is available from Kent-Moore: part #J-36567, which costs
around $275.00 plus shipping. Springs can not be removed or
installed without this tool. If you are interested in putting
custom springs on the front of your Impulse JR, you will need to
obtain one of these tools, borrow one from a dealer, find a shop
that has one, or have a dealer install the springs for you (this
is a required tool for dealers shops).
In addition, you will need a tie rod end remover or compact puller
($35+) to remove the ball joints and tie rod ends from the spindle
and a 30 mm end wrench ($20) to remove the strut bars from the lower
arm.
Rack and Pinion Bushings:
If you are finding your steering wheel is not centered after you have the
alignment set, or your steering is sloppy, it is likely that the bushings
on your rack-and-pinion assembly are bad. Replacing these is not overly
difficult, and you can probably do this if you have enough tools to
change your oil. On the JR, the bushings are between the "C" shaped
clamps and the housing, where it bolts to the main frame cross
member. Remember to soak the bolts in Liquid Wrench
for awhile before you ever get a socket close to it, or you will
break the bolts off and have to pull the engine to drill the
bolt out and retap the fitting. The bushings are relatively
inexpensive.
Sway Bar Bushings:
If you are going to try to improve your handling, sway bars are your
first step. And while you're replacing your OEM bars, you should put on
poly urethane bushings while you are at it. On the JR with the three link
rear end, the rear bushings on the bar-to-body clamp, or center mount, can
be replaced with any standard clamp set with slotted mount points. Dee's
and Energy Suspension both make a perfect replacement in their mini line of
smaller sizes. The front center mounts are a bit of a challenge because the
mounting holes are staggered and the front skid plate or rock guard
mounts to the bracket. You must use a smaller size
clamp, as in the Prothane mini line. Hold the original clamp over
the new clamp, and mark the holes of the original
clamp onto the new clamp. You will have to use a Dremmel Moto Tool
or similar, with a small grinding bit, to grind the
new clamp to the pattern of the old clamp. Then, when you mount the
bar, mount the old clamp (without it's bushing)
over the new clamp, with the new buching around the bar.
The end links and bushings on the front should be replaced also with
polyurethane pieces. The front end links are of an odd size, so buy the
next size larger than you need, and cut the metal tubes to the propper
length with a saw or Dremel Moto Tool. The rear end links are of a rather
uniqur design, and I have not found a poly urethane replacement for them.
Aerodynamic Kits for Impulse and Piazza JR:
Several companies offer Aero kits for the Impulse JR, but I haven't
found any that fit very well at all. These kits consist of front
and rear fascia pieces and side rocker skirts that fit OVER the
front and rear urethane bumpers and OVER the rocker covers. They
are made of thin, rigid, brittle fiberglass and attach with sheet
metal screws. Most people realize that this description invites
rust and broken body work. These body pieces are second and third
generation moldings from paterns that did not fit well to begin
with, and fit worse now. In addition, the $1000.00 plus cost of
these kits is well above comparable kits for other vehicles which
fit much better. In the absence of any after market option,
owners of non-turbo and early Impulse JR models can opt to install
factory Isuzu front air dams and rear spoilers from turbo model
Impulse JR's. These parts are available from Isuzu parts
departments and fit all Impulse JR's, but are expensive: $330.00
for the air dam and $520.00 for the rear spoiler and brake light.
However, these parts were designed and built to exacting
specifications and fit perfectly. Another option is to obtain
these parts from a salvage/junk yard where they will cost
significantly less than from Isuzu.
It is important to point out that the addition of the front air dam and
the rear spoiler will drop the coefficient of drag on the Impulse
JR from .36-.37 to .33. This is a ten percent improvement and
while you may not be able to tell the performance difference at
any semblance of a reasonable or legal speed, you will notice
improved gas milage.
Rust prone spot on the Impulse and Piazza JR:
Keep an eye on the fender skirts, just below the shock absorber mount.
The fender skirt is made of double wall
sheet steel, and there is no seal to keep out water or dirt.
Salt and water will collect here, especially on the
passenger side (the road crowns in the middle and the passenger
side is exposed to more puddles). The rust
starts as a bubbled spot. Eventually, you will find a hole
about the size of a quarter here. The fender skirt is a
rather important piece, in that it is a structural piece, and
incorporates the upper shock mount. You can't just
weld around on this to patch it up without taking the temper
out of it or causing structural damage, and replacing
it costs around $1500. Finding this on your own vehicle is not
good, but if you are buying an Impulse or Piazza,
keep an eye out, this is comparable to checking for rust holes
under the battery on a VW Beetle.
Other places to look out for rust: under the battery, the rear edge of
the roof below the upper edge of the trunk lid, the tailgate below the
tail lights along the top edge, behind the top edge of the rear bumper,
and on the forward edge of the rear wheel arches.
Fender Liners on Impulse Piazza JR:
The plastic fender liners on the JR are important to keep the water away
from the fender skirts. Unfortunately, the lower ends, toward the rear of
the front wheel well have a habit of coming out from where they are
tucked into the rocker panel covers, flipping up, and riding on the
tire. The first thing you will notice is a rumpling sound while the
plactic rubs along the tread, and this may seem harmless enough, unless
you are travelling at highway speed and don't notice until the tread has
cut through the liner leaving a big hole, and you have to replace the
liner at a cost of about $18 each.
Touch Up Paint Tip
When tryiing to touch up rock chips, I have found the following to be a
very good technique, but you should try it on a spot that is not highly
visible or out in the middle of a body panel to see if it will work on
your paint.
After thoroughly washing and drying the paint, wipe the area that you
will be working on with denatured alcohol and a paper towel. Dab your
touch up paint on and into the chip hole. Wait for it to dry a while,
and then use fast drying enamel reducer wo wipe away the excess so that
only the paint in the chip hole remains.
Again, test this on an area like the wheel well lip or low on the rear
bumper or rocker cover to make sure that you don't pick up the rest of
the paint with the enamel reducer. It works well on polyurethane paint
with clear coat, and leaves very little trace of any paint imperfection.
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