Thread: 97 Grand Prix GTP with Intermittent #4 Cylinder Misfire

Originally Posted by srlash

Hello All,

I have been trying for the better part of 2 months now to
isolate a number 4 cylinder misfire with no luck. I have put new
plugs,wires and coils in with no help. I have changed the fuel
injector;no dice, misfire still present. Took the car to Pontiac
where a compression check passed. They had the car for
over 3 hours and could not pin anything down. Did mention that
the PCM driver circuit for number 4 fuel injector could be failing,
but they were not sure. Got a used PCM with the latest GM
software and still number 4 cylinder misfire. I have checked the
the wiring to the injector with a home made LED and ran this
inside the car. While the misfire is occuring the LED flashes
nomally, so it appears the driver circuit for the injector is intact.
Next tried hooking up the LED to the primary wires below the
number 4 coil pack, no problems here either when car is misfiring
the LED flashes normally. The hot wire to the injector is not breaking
down either as this was checked as well with a wire running inside the
car hooked up to multimeter. Meter showed 14 volts while misfire was
ocurring. The car has 112,000 miles on it and I am the original owner.
I thought perhaps knock sensors so I scanned the engine and here is
where things get interesting. At idle the scanner shows -22 degrees
ignition advance, does this make any sense. I scanned my fathers
2003 Caddy and got a reading of 9 degrees advance. How can my car
run at minus 22 degrees advance. Heres my question, is this a normal
reading for a car that is supercharged or are these readings way off which
I am inclined to believe. Appreciate any info you all are willing to part
with and sorry for being so long winded.

Thanks,

Steve

Hi All,

My Bad, I guess the scanner that I have reads a little different on
my car. I guess the -22 degree reading is actaully BTDC and not
ATDC like I originally thought. Sorry to trouble you all !!!

Steve

What does the #4 plug look like?

How about switching injectors to see if the problem follows it.

Originally Posted by Keet04GTP

That is way off... What have you done to the car? (mods) (new parts besides the ones listed above)

Thanks for the Reply,

Sir, I have done absolutely nothing to the car. The car is 100% stock
like the day I bought it from the showroom floor. So the ignition timing
is off I take it from your response. What should the timimg read at idle.
Is it possible the timing chain might have slipped a tooth. I have swapped
the injectors and the problem does not follow the injector. I have since
bought a new injector for number 4 cylinder. Still no help. The #4 plug
is not revealing anything either. It looks pretty much like the other 5.

Thanks,

Steve

I'm also assuming that you've switched around the coil packs?

Yes, and problem stays with the #4 cylinder. Just wondering does anyone here have
the specs for ignition advance on a 97 Grand Prix GTP at idle, I mean does the number
I am getting -22 degrees make any sense. Oh by the way, I purchased a new coil for
#4 cyclinder and no help.

Appreciate the Quick Feedback,

Steve

The actual timing on the idle should be around 22 degrees, that sounds about right.

It is common to have a random misfire, but a multiple misfire that brings on the SES light could very well be a concern. I'll do some digging and see what I can find.

are there any other codes that come up?

Reptile,

When nailing the car for 5-6 seconds this will bring on a flashing SES light for about
7-10 seconds followed by a steady SES light. When checking for codes there is
nothing, no codes period. When setting the scanner to monitor mode #4 cylinder
is intermittently misfiring. I would have to say less intermittent and more actively
missfiring is I would have to characterize it. It can not go 2-3 minutes without
missfiring.

Appreciate Your Help,

Steve

Could this condition escape a compression check. It occasionaly misfires at idle
as well. Pontiac had the car for the better part of 3 hours and claims the engine
is mechanically sound, although I wonder sometimes how thorough they were
with the compression check. I wonder if an Ignition Control Module could cause
a single cylinder misfire. Pontiac tells me that the ignition module is ok ???

Steve

If a lifter were to fail, you can usually hear it. Even if it were something along those lines it would most likely be constant and not intermittent. It also could very well be an ignition module.

Reptile, that is what is such a pain in the arse with this car. I have driven a car
with a burnt valve and it is a constant miss every time that valve opens it stutters.
Perhaps a weak valve spring that allows the valve to float at higher rpms but that
would not explain the miss at idle that I occasionaly have. I thought a blown
head gasket between cylinders, but then I suppose I would have 2 cylinders
misfiring.Maybe a worn camshaft???

Steve

Unless there is some type of internal engine failure, these camshafts don't wear out. They are a roller cam and hardly wear at all. However, given if there are a ton of miles on the engine, it could just be wearing out. Maybe carbon buildup on the valve...try seafoaming it. Weak valve springs can be it....it's just a bunch of possibilities that you just have to go through by the process of elimination.


If it flashes the SES code then there should be something in the PCM like a P0300 code.

An ignition module may be the culprit here, but I can't really say for sure.

Reptile, At this time I agree with you, I think it is something electrical.
Sometimes I can nail the car and when it shifts from 1st to 2nd gear the
whole front end pulls up somewhat. It has plenty of power when it doesn't
misfire. The question is, are there any other sensors that could cause a
single cyclinder misfire. I am leaning toward the ICM as well, but from
everything I have read on the internet, if it is failing then the companion
cylinder should be misfiring as well. I guess there are exceptions.

Steve

I have 1997 Grand Prix 3800 Supercharged with the same problem. mine is running at -20. I have replaced fuel filter, figured cheapest first, plugs, wires, havent gotten to the coil packs yet. money is super tight. My car will keep dying out though. Nobody has any idea what the problem could be. Any suggestions will be greatly appreciated. Is it possible to swap out coil packs to test for spark? on the same car, not from a different one.

thanks again

--Justin

Originally Posted by srlash

Hey All

I have been trying for the better part of 2 months now to
isolate a number 4 cylinder misfire with no luck. I have put new
plugs,wires and coils in with no help. I have changed the fuel
injector;no dice, misfire still present. Took the car to Pontiac
where a compression check passed. They had the car for
over 3 hours and could not pin anything down. Did mention that
the PCM driver circuit for number 4 fuel injector could be failing,
but they were not sure. Got a used PCM with the latest GM
software and still number 4 cylinder misfire. I have checked the
the wiring to the injector with a home made LED and ran this
inside the car. While the misfire is occuring the LED flashes
nomally, so it appears the driver circuit for the injector is intact.
Next tried hooking up the LED to the primary wires below the
number 4 coil pack, no problems here either when car is misfiring
the LED flashes normally. The hot wire to the injector is not breaking
down either as this was checked as well with a wire running inside the
car hooked up to multimeter. Meter showed 14 volts while misfire was
ocurring. The car has 112,000 miles on it and I am the original owner.
I thought perhaps knock sensors so I scanned the engine and here is
where things get interesting. At idle the scanner shows -22 degrees
ignition advance, does this make any sense. I scanned my fathers
2003 Caddy and got a reading of 9 degrees advance. How can my car
run at minus 22 degrees advance. Heres my question, is this a normal
reading for a car that is supercharged or are these readings way off which
I am inclined to believe. Appreciate any info you all are willing to part
with and sorry for being so long winded.

Thanks,

Steve

Hello Jmoney,

Yes you can swap the coil packs as they are all indentical. What
I ended up doing was removing the supercharger belt and the high
speed fuel relay in the underhood electrical relay center. Problematic
missfire gone. Next I ended up changing the coolant themostat. Car
runs very well now. I suspect my car was never fully warmed up and
was receiving too much fuel and when scanning the the car I always
had 10% more fuel added to the base fuel curve. I have not hooked
up the supercharger belt yet since I have to replace the snout drive
seal due to it is leaking all over the place. Perhaps since the car was
receiving too much fuel, and under supercharged conditions it was
missfiring. I might also add that when the thermostat was failing I
lost about 2 miles per gallon in fuel economy.

Good Luck and keep me posted,
Steve

Are you by any chance slowly losing coolant from your coolant recovery bottle?

Are you aware of the LIM gasket issue on these engines?

Impossible-to-trace misfires are sometimes a symptom of leaky LIM gaskets, intermittently wicking coolant into one or more cylinders.

i'm having the EXACT same problem with my car!! the only thing is i'm n/a.. same cylinder.. same symptoms.. checked the same things.. and just about the same amount of miles.. anyone have any info that can possibly help me?