Grand Am 3.1 1997, p0300 random misfire but mostly cyl#3 when in P or N only

[Aki334]

this one is very strange, no check engine light for now, but I was able to use otc genesys scanner to see that #3 cyl is misfiring mostly when engine is in Park or Neutral, this car has a lot of power when driving and I do not notice any other problems besides engine shaking in Park. I checked vacuum pressure with my vacuum pump and it shows 17 Hg in and it goes up and down by .5 Hg in. Since this happens as soon as I put my car in park, can I assume there is something wrong with PRNDL switch under the hood. Or is there something wrong with my valves on that cylinder. What happens with the oil pressure when the car is in park and when car is put into D?
Any help here would be very apreciated. Thanks in advance Aki

[xeroinfinity]

Welcome to AF !

Could be several items here that are causing this.

I'd start by first checking all the vacum hoses for leaks or brakes in them. Essecially around the intake manifold.

Then if the fuel filters not been changed in the past 30k miles, might try changing that and see if it clears up.

Could also be faulty/incorrect gaped spark plugs.
Bad plug wires, ignition coils faulty or weak.

And your injectors could also be clogged/dirty.

Lastly the injector wires are known to get small breaks in them and cause misfires.

Hope that helps !

[Aki334]

Thanks for your advices, let me start from the begining how this problem started. 3 years ago my car developed that small engine shake problem in at first it did not bother me so much, but then startet to go on my nerves. So one day I put some gas in my car, and went to a restaurant to eat sometning up to that point everything was fine, but that little engine shake and I never had MIL come on before. So after restaurant I started my car and there it was that yellow MIL came on and it was flashing my engine was shaking 30 times worse now. Came home connected my OBD II scanner and P0303 code was shown. Ok Cyl #3 was problem. So I started from chepest solutions to up car had 22000 milles at that time. Changed spark plugs - did not help, checked cables - looked good but still changed - this did not help, ok bought new injector put it instead of injector #3 and the problem was solved. However that small shake did not go away. So I changed fuel filter, fuel pressure regulator oxygen sensor before cat, all vacuume lines vere checked and clamped at ends to make sure everything is tight, cleaned throttile body and still same thing. Now with my new scanner I can see all engine parameters including engine misfire section where you can monitor all cylinders and their hystory of misfiring. So you will not beleve #3 is problem again, but why it is brand new. Another thing scanner shows me this "injector fault - No" so this could mean that wires are all good for injectors and I did check each injector cable for continuity to 10 way connector. Map sensor is also good. I was also able to check other things with my scanner and this one is interesting "TID:02 CID:04 failed, STEADY ST CRUS CAT EFF TEST B1 FAILED (IT HAD SOME MAX AND MIN LIMIT NUMBERS), EGR CRUISE FAILED, EGR DECEL TEST FAILED. Ok I did clean EGR still no difference, then installed another one from junk yard no difference, changed coil for 6/3 no difference, changed ICM no difference. So what is going one here????? I checked PCM connector for #3 injector to 10 way injector connector #3 injector and it was fine. Even took that 10 way connector out and put straight wires instead just to eliminate possible intermitent connector problem and still no difference............ Now I am thinking about possible bad valve spring on one of the two valves for #3 cyl, or bad PRNDL SWITCH.

[maxwedge]

I would do a leak down test, not a compression test, to rule out internal problems, although a bad valve spring, not common here, will not show up on the leak down test. Any issues with the color of the plug in that cylinder? Can you do a power balance/injector test on your scanner, if so do it also. A misfire can cause poor cat efficency as the xcess o2 cannot be completely burnt in the cat and the post cat sensor will be skewed. Remember a misfire code precludes an actual cat efficiency code.

[xeroinfinity]

With the engine shaking around I'd almost say you might have an engine mount damaged/broken.

I'm not familar with the genesys systems.

If the EGR passages arent open, this can also cause misfires.
But it sounds like you have replaced about everything so you should be narrowing it down.

On the PN switch ,
your scanner doesnt scann this ?
I Might be able to find the test procedures somewhere If you need.

Also how many miles are on your 3.1 ?

And to ask a silly question, have you replaced the PCV latly?

[Aki334]

YES I DID CHANGE PCV VALVE AND THE RUBBER PART. I BOUGHT THIS CAR IN 1997 BRAND NEW, IT IS STRANGE BUT THIS CAR HAS ONLY 28000 MILES. IT WAS SITTING IN MY GARAGE FOR ALMOST 8 YEARS WHILE I WAS STATIONED IN EUROPE. YES I DID DRIVE THIS CAR FOR ABOUT 15 DAYS EVERY SIX MONTHS, AND IN THE MEAN TIME I DID HAVE SOMENE WHO WAS STARING MY GA EVERY 10-15 DAYS. ANOTHER VERY IMPORTANT THING TO MENTION IS THAT WHEN I START MY GA IN THE MORNING I CAN SMELL STRONG EXHAUST FUMES AND I DO NOT THINK I EVER SMELLED SOMETHING SIMILAR ON OTHER CARS - MAYBE THIS CAN HELP YOU TO HELP ME .
ALSO TO ANSWER MAXWEDGE'S QUESTION: NO I CAN NOT DO power balance/injector test WITH MY SCANER, UNLESS "INJECTOR FAULT-NO" SHOWN BY THIS SCANER IS THE SAME THING. HERE IS ALSO ONE THING TO THINK ABOUT AS YOU ALREADY ALL KNOW 2 4 6 FROM LEFT TO RIGHT ON THE FRONT AND 1 3 6 L-R ON THE BACK - P0300 FOR #3 AND #4 BUT AS I SAID #3 MOSTLY. YOU PROBABLY KNOW WHERE I AM LEADING WITH THIS THERE MUST BE SOME KIND OF PROBLEM WITH OPPOSITE CYLINDERS 3 AND 4. BUT AGAIN IF THERE IS SOME KIND OF INTERNAL ENGINE PROBLEM WHY WOULD'T I HAVE THE SAME PROBLEM WHEN THE CAR IS IN D AND IDLING OR WHEN I AM DRIVING AT NORMAL OR FAST SPEEDS? I AM NOT SAYING THAT MY CAR IS NOT MISFIRING DURRING THAT TIME BUT IT IS ONLY ONCE IN A BLUE MOON, OR SOMETIMES NEVER. AGAIN, MIL IS NOT ON, BUT THIS SCANNER CAN SEE THIS. THIS MUST BE SOME KIND OF SIMPLE ELECTRICAL PROBLEM. ANYWAY THANX GUYS FOR YOUR EFFORT AND EXCUSE ME FOR MY GRAMMAR .THIS IS MY THIRD LANGUAGE.

[xeroinfinity]

Aki334, please refrain from using CAPS !
I can see just fine , it makes it seem like you are yelling

Ok since the car only has 28K miles, and it has sit for 8 years, I'd bet your fuel is contaminated with moisture.

-When you run the tank low do these symptoms get worse?

Might try some fuel dryer , You might consider pulling the tank and see if its full of debrie or varnish looking fuel that could partially clog your screen filter on the fuel pump.

With that low of miles you can probly rule out any internal troubles causing this.

One other thing I would do , is get the fuel sytem cleaned.
From sitting It could have varnish(debrie) inside the lines and little flakes come loose and clog #3 or #4.
The reason would be they are in the middle of the fuel rails,
so pressures are lower in the middle then on the ends, thus allowing things to build up on injectors 3 & 4.

Just my hypothisis.

FYI-90% of MY misfires have been the injectors/fuel related.

Good Luck!

[Aki334]

Sorry for the caps it was on by accident. Ok hmmmmmmmm I like your thinking about the middle pressure problem in the fuel rails for #3 and #4 maybe 41 psi for 41-47psi in specs is too low. Maybe I need to increase my pressure somehow. And you know what you are probably very very close, becasue when I was changning my fuel pressure regulator I was pinching rubber fuel lines to test pressure regulator with the fuel pressure gauge and at one point I noticed that idle was perfect like never before. We have similar thinking about this problem that is why I also cut the fuel inlet line 2 ft before the injector fuel rail and instaled small inline fuel filter no leaks (just a second line of deffense) . So now what do you think if I instal fuel gauge to the shrader valve on the fuel rail and use a smal clamp to tighten the return line from the rail after the fuel pressure just enough until I see that pressure raise to 47 psi and leave it like that? Do you think this will work for the pressure at least? What happens to the fuel pressure when you shift from P to D? I will check this and if I see that the pressure jumps up that is it the problem will be solved I will clean fuel pump screen and fuel injector rail. Thanks xeroinfinity.
and please if you know specs for coil pack primary resistance for this car let me know.

[xeroinfinity]

First of thier should not be any rubber fuel lines under the hood. It was probley a vacum hose and that would indicate, to me, that you have a vacum leak somewhere.

Clamping it wont raise the pressure. At idle 41-42psi is normal, under heavy loads it raises it self through the vacum.

Heres a pic that explains the coils and how to test them.
Testing the HEI ignition coil

Also here is the page that it came from might find some helpful info.
autozone

Hope that helps!

[Aki334]

Xeroinfinity - Thank

[Aki334]

I already wrote my replay, but it looks like it did not end up here. In short finally I solved my problem for p0300. Spec for fuel pressure was 41-47psi for my GA 3.1 L and I did have 41psi but that probablly was not enough. What I did is, I tightened a clamped just a bit aroung the outlet fuel line right after the fuel pressure regulator and I noticed significant difference in engine idle and shaking thing disapeared. I did not check my fuel pressure with the gauge, but I will do it later. I hope by doing this I will be able to tighten or loosen the same clamp to get 47psi or maybe I will go for 45psi to be on the safe side. Now since my fuel filter is one month old, can I assume that the fuel pump filter is dirty or as XSEROINFINITY said it could be cloged fuel injector rail.
Thanx Xeronfinity your helped me stay on the right path for this problem and we did it.