97 Grand Prix With Intermittent Miss

[srlash]

Hello Everyone,

I have been following this forum for some time now and
finally decided to join. I have a 97 Grand Prix GTP with
110,000 thousand miles on it. I am having a problem with
and intermittent miss which is going to drive me in the nut
house. I had a friend hook up a scanner and we discovered
number 3 cylinder had over 200 missfires and number 4
cylinder had over 16,000 missfires in history. When scanning
in real time mode number 4 cylinder was actively missfiring.
So I changed all 3 coil packs, plugs and wires. Car starts much
faster now when cold and idle quality has improved significantly.
However, the miss still persists. I have done a fuel pressure
check and the readings appear to be good with the vacuum
applied and disconncted from the FPR. The fuel pressure is holding
solid after the 2 second initial prime. I have removed the throttle
body and did a thorough cleaning with electrical components removed
of course, and the air filter was also replaced. The problem still persists.
Fuel pump and fuel filter are newer as they were replaced at around
70,000 due to internal check valve failure inside pump. The miss seems
more pronouced when the TCC is engaged suppose something to do with
the direct connection. The TCC does engage around 35 mph and when you
tap the brake it disengages. It will also release when accelerating briskly.
When in the higher RPM range such as flooring the pedal you can then really
feel the car miss and on occasion the car backfires. My thinking is either
the crankshaft sensor or MAF sensor but don't want to keep throwing parts
at it till I am reasonably sure of either one. The PCM is not giving up any
secrets either, no SES light and no codes stored checked several times.

Thanks for any info you are willing to part with and sorry for the long winded
post. I just thought I would give all the facts so a reasonable conclusion
can be reached.

Once Again Thanks Everyone,
Steve

[rkvons]

How about fuel system cleaner? Not just any. Try Chevron Techron. Red bottle. Get two of them. Do 12 gallons of fuel with one bottle, run it out and repeat. I think You'll be pleasantly surprised.

[srlash]

Originally Posted by rkvons

How about fuel system cleaner? Not just any. Try Chevron Techron. Red bottle. Get two of them. Do 12 gallons of fuel with one bottle, run it out and repeat. I think You'll be pleasantly surprised.

I have run 2 cans of B+G 40 fuel systems cleaner which from what I
understand is hard to beat as far as cleaning the fuel system, and still
no joy !!!

[richtazz]

How long have you owned this car?
Do you run 87 octane in it on a regular basis?

I would strongly suggest doing a compression test. The #4 cylinder is the one most prone to detonation damage due to running 87 octane if you or the previous owner have made this mistake. It's also the most common cylinder to develop head gasket issues on these engines due to being in the center in the rear (less external surface area and airflow). Since you also have misfires in Cyl #3 (the center one in the front bank), it points even more toward possible head gasket issues.

[srlash]

Originally Posted by richtazz

How long have you owned this car?
Do you run 87 octane in it on a regular basis?

I would strongly suggest doing a compression test. The #4 cylinder is the one most prone to detonation damage due to running 87 octane if you or the previous owner have made this mistake. It's also the most common cylinder to develop head gasket issues on these engines due to being in the center in the rear (less external surface area and airflow). Since you also have misfires in Cyl #3 (the center one in the front bank), it points even more toward possible head gasket issues.

Good sugestion, but would I not have coolant
loss or the typical white smoke in the exhaust
from a blown head gasket. I have neither at this
time. I have checked the oil and it does not exhibit
the charistic coffee and cream look if water were mixing
with the oil.

Thanks for the quick response !!!

Steve

[tblake]

Originally Posted by srlash

Good sugestion, but would I not have coolant loss or the typical white smoke in the exhaust from a blown head gasket.

In a word No. What if a headgasket blows between cylinders?

I realize my opinion doesn't mean much, but I agree with Rich, with any missfire problems, especially ones that can be narrowed down to a specific cylinder like #3 or #4. A person can waste a TON of money throwing parts at it and feel like a real idiot when they finally realize that a valve is burnt or a piston is cracked.

Originally Posted by srlash

The fuel pressure is holding solid after the 2 second initial prime.

Whats this mean? You have to turn the key on, off, then back on in order for the fuel system to build and hold adequate pressure? Thats not normal, the pressure should build and hold with the first key on prime.

[srlash]

Originally Posted by tblake

In a word No. What if a headgasket blows between cylinders?

I realize my opinion doesn't mean much, but I agree with Rich, with any missfire problems, especially ones that can be narrowed down to a specific cylinder like #3 or #4. A person can waste a TON of money throwing parts at it and feel like a real idiot when they finally realize that a valve is burnt or a piston is cracked.



Whats this mean? You have to turn the key on, off, then back on in order for the fuel system to build and hold adequate pressure? Thats not normal, the pressure should build and hold with the first key on prime.

When the key is turned on the first time the pressure builds and holds,
I don't have to keep turning the key on and off to build up pressure.
Disconnected MAF sensor and ran car with no real change, car still
intemittently missfires. Popped hood and noticed that both exhaust
manifolds were glowing as if someone applied a blow torch to them. Allowed
car to cool down and reconnected MAF sensor and then ran car some more
to verify that the glowing manifolds was not a result of the sensor being
disconnected. Once again both manifolds were glowing a nice orange
color. Is it possible that the crank sensor is starting to fail allowing
combustion to take place in the exhaust manifold ?

Once Again Thanks Guys for Your Input !!!
Steve

[tblake]

Nope, I'm not quiet sure....

I know cat converters will glow red hot if the motor runs really rich.

But I think you may have a lean condition. Have you replaced the fuel filter? What are your exact fuel pressure readings?

[srlash]

Originally Posted by tblake

Nope, I'm not quiet sure....

I know cat converters will glow red hot if the motor runs really rich.

But I think you may have a lean condition. Have you replaced the fuel filter? What are your exact fuel pressure readings?

I guess I should be more specific when describing stuff. The exhaust
manifold only glows red just a ways below number #5 cylinder and just
below number #4 cylinder. I don't believe I have intake manifold gasket
issues as the car runs dead to rights at 700-750 rpm at idle. I know I
should probably check with a vacuum gage but I just don't have the
luxury of spare time as I am taking care of ageing parents. I did stop by
the Pontiac dealership today and discussed the symtoms with service
advisor and he felt that if crank sensor was failing it should throw a code.
He did mention that perhaps it might be leaking fuel injectors or possibly
faulty injectors which I am more inclined to agree with. The fuel readings
which you are wondering about are dead on per the GM service manuals.
The pressure holds well at first key on. It can go 30-40 minutes before
losing some pressure. Not sure about the cat though, if I step on the gas
hard wow does the car ever move out. No power drop off what so ever,
the car easily does 70 just like it was new. I just have this darn missfire which
is random at best. As I mentioned earlier time is a luxury I dont have much
of so I have decided to let the Pontiac dealership down the road see what
they can find with their scanning equipment. Could be the best 100.00
dollars spent.

Appreciate your interest in this problem and I will update tomorrow,

Thanks Again, Steve

[richtazz]

Tim, don't short change yourself, give yourself some credit as your opinion does matter. You give solid advice based on what you've learned both hands on and from what you've read. You've been an asset to AF since you owned your Lumina, and nothing has changed since you got your GTP and came over here.

Srlash, not all head gasket leaks result in coolant loss or coolant/oil contamination. As Tim stated, you could have a compression leak between cylinders. Burnt valves and pistons can also cause compression loss and a resultant mis-fire. Cylinders 4 and 5 are the most prone to develop these as well, again due to the fact that they run a little hotter than the other 4 cylinders. It sucks you don't have time and had to take it in, but please let us know the outcome. We hate threads that have no resolution and your answer may help others in the future.

[srlash]

Originally Posted by richtazz

Tim, don't short change yourself, give yourself some credit as your opinion does matter. You give solid advice based on what you've learned both hands on and from what you've read. You've been an asset to AF since you owned your Lumina, and nothing has changed since you got your GTP and came over here.

Srlash, not all head gasket leaks result in coolant loss or coolant/oil contamination. As Tim stated, you could have a compression leak between cylinders. Burnt valves and pistons can also cause compression loss and a resultant mis-fire. Cylinders 4 and 5 are the most prone to develop these as well, again due to the fact that they run a little hotter than the other 4 cylinders. It sucks you don't have time and had to take it in, but please let us know the outcome. We hate threads that have no resolution and your answer may help others in the future.

Richtazz and Tblake,

I did not mean to question your suggestions as far as a blown head gasket
as I am certainly not an expert by any means. I hope I have not offended
either of you and I do appreciate both of your input. I had never heard of
a blown head gasket between cylinders so now I have learned something new
which is what this forum is all about. Pontiac dealership called and I will let
you know what they said, "it is not going to be easy to fix this car". Gotta
run right now, old people are keeping me on the run !!!

Steve

[richtazz]

No offense taken Steve. You've got a bit of a head scratcher here, so we're throwing it all out there, just in case you didn't think of something.

On the keep it simple side of things, I would also double check the spark plugs to make sure that you didn't accidentally crack one while installing them. It's a fairly common occurrance with the rear plugs, since they're so easy to get to !

[tblake]

So Steve, the dealership called you back an said the car wont be easy to fix? Uh Oh, doesnt sound good!

BTW, thanks for the comments Rich, I really appreciate it. However I doubt I will ever be as knowledgable as you moderators/advisors.

[srlash]

Originally Posted by tblake

So Steve, the dealership called you back an said the car wont be easy to fix? Uh Oh, doesnt sound good!

BTW, thanks for the comments Rich, I really appreciate it. However I doubt I will ever be as knowledgable as you moderators/advisors.

Hello Again Guys,

Well picked up the car from the dealership, and spoke with the
service advisor and here is what he had to say. I was only charged for
1 hour of diagnostic service and they spent a total of 3 hours with the car.
They are pretty decent people to deal with. Now for the problem at hand;
the car has a steady missfire at 3000 rpm. A little less or more rpm and the
miss will stop. They checked everything from soup to nuts. They did a
compression check on all cylinders was informed compression was good on
all cylinders. They checked fuel injectors and said they all passed as well.
They double checked my work as well, swapping coils,checking plugs for
cracked insulators like you guys suggested and still nothing concrete. The
crank sensor, mass air flow sensor and all the other sensors pass all the
diagnostic checks and none of the sensors are throwing any codes. Oh by
the way, the missfire is on number 4 cylinder. They did not mention if they
performed a vacumm check I can only assume that one was done. They said
that what I have is very unusual in that #4 cylinder only missfires at 3000 rpm.
They hinted that perhaps the PCM was failing but did not want to suggest that
as this part is extremly expensive. Any suggestions guys as I am sure as hell out
of ideas. Oh sorry they did say that the intake manifold gasket was ok, age
catching up wih me HA.

Thanks for any info !!!
Steve

[tblake]

Wow, that is an interesting problem....

I'm stumped!

Will it missfire in park at 3000rpm's?

You can do like Rich stated in a different post.... Use an inductive timing light on the number 4 sparkplug wire, have a buddy hold the rpms at 3000 so it misses, then aim the timing light at the underside of the hood as you watch the spark pattern by the light flashes or lack of.

This might help you narrow it down to either ignition or fuel related. It sounds as though your motor is mechanically sound, so thats good!

If you dont have a timing light, I think you should be able to rent one from a place like autozone, usually free if you return it the same day. Just do your diagnosis in the parking lot and return it within 15 minutes.