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P0302 Misfire Code - 2004 Pontiac Grand Prix N/A 3800

the magnet it to remove the locks, they are very light, this is a safe way to get them out. and if you drop one putting them back in you can use the magnet to fish around the top of the head for it.
 


Does anyone have a part number for the correct valve stem seals? I'm trying to source a complete set so I can order them quickly if needed. I keep finding different pictures and some look like O Rings, others look sort of like a sleeve, and others look just like a thick seal with a clamp around them. That being said, I'm not certain which ones to try sourcing.
 
Will do if needed. Thanks.

Now to change things up to eliminate the fact that I had the double platinum plugs in there - I went and purchased a brand new set of the AC Delco 41-101 Iridiums and put them in tonight. Gapped .060 and I just got back from a test drive. Unfortunately, the P0302 code still shows up and does the same exact thing it had been doing.

Once the engine cools down, I'll re-gap to .050 and see if it does anything.
 
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if you take the springs off. change the seals. its worth the few bucks. they take nothing to swap out too. pull em off. push the new one on.

the felpros came with a plastic sleeve to put over the valve end too so the seal dont hang up and get damaged on the recessed valve lock area.
 
It doesn't like the .050 gapping. Almost instantly to a P0302 code as soon as it gets put into gear. I'm going to put it back to .060 so everything is back to what it should be at.

I'm guessing the next step after that is going to be to remove the valve cover and see what it looks like in there?
 


I've put it back to .060 and test drove it again. Now it seems that the P0302 code is flashing intermittantly only while in gear at a stop sign/light. The CEL only went solid one time this go around. Seems to flash 10-15 times and then stops. I can pull the code under pending codes option, but not under actual read codes option. Under Read Codes, with CEL flashing, it says no faults, system pass. Under Pending Codes, it shows the P0302 code.
 
It seems like the CEL will only start flashing while in drive or reverse, at an idle, for a period of time and it seems to be clearing itself before it sets the CEL to a steady on. So long as the vehicle is being driven, the CEL does not flash or come on steady. Still no other codes either. Maybe I should have my daughter drive it for a few days and we'll just keep an eye on what that CEL does. Maybe it will work itself out once the PCM relearns that everything is new and it relearns/resets - if that is something these vehicles do. This is looking almost like how it was doing when I had the P0303 code back when I got it and it worked itself clear after about a month.
 


Pooterosa said:
I am sorry if this thread is in the wrong spot. I was looking for another one regarding misfires but I did not see one.

I have a 2004 Grand Prix N/A 3800 with 140,100 miles on it. It is giving the P0302 Cylinder 2 Misfire code while at idle. It does have a rough idle and shifts into reverse and drive with sort of a clunk too (more so into drive than reverse). You can feel the misfire at idle and you can see it on the tach. Other than at idle, the car runs, drives, and shifts perfectly fine. The CEL light will start off by flashing and if you take off driving, such as from a stop sign/light, the CEL will go off. If you leave the car sit there and warm up, the CEL will go to a steady light and I have to clear it with my scan tool. (I do have an Actron CP9185 and a Scanguage II if anyone needs me to run some tests for a particular reading for troubleshooting this issue).

Before we go through exchanging a bunch of messages about what has or has not been checked, I'll provide a listing below of what I have either verified, or have replaced.

Spark Plugs - New AC Delco Double Platinum - Gap 0.60
Spark Plug Wires - New
EGR Valve - New
MAP Sensor - New
PCV Valve - New
MAF Sensor - New
Camshaft Position Sensor - New
Crankshaft Position Sensor - New
Ignition Coils - All 3 - New
ICM - Used. Tested as good.
Fuel Injection Pressure (at fuel rail) - Tested good @ 56
Fuel Injectors - Noid Light Tested. Number 2 is new. I even went one by one and unplugged them and verified that the idle changed when unplugged and idle restored after plugging them back in. I moved the original #2 injector to #4 and the issue stays on #2, even with a new injector.
Compression Test - May need to be redone but the last time I checked it a couple of months ago it was at 137 on the #2 cylinder. Without having my notes in front of me, the best I can remember, all of them were above 130.
Air Filter - New
Head Gaskets - 6 months old
Upper and Lower Intake Gaskets - 6 months old - No leaks that I have been able to locate. No leaking antifreeze through tailpipes or on the ground, no oil in water or visa versa. Everything checks out fine in that aspect.
Coolant Temp Sensor (and plug) - New
Thermostat - New
Throttle Body - Cleaned

Are there some vacuum lines somewhere that I have not located that could be causing this?
Click to expand...

I saw you already changed the MAF sensor, but if you did not use a new Acdelco part that could be the problem. I have learned my lesson with using non-acdelco MAF the hard way with getting a single misfire on only one cylinder when everything else is up to par. Once I put the new stock Acdelco MAF the single cylinder misfire disappears completely. Worth a try.:th_thumbsup-wink:
 
Well, I've just finished replacing the valve stem seals and unfortunately, the P0302 code is still coming on. I took it on about a 20 mile road trip and just got back. While it does seem to actually run better, and that obnoxious little "chatter" I referenced before is gone, it still shows an intermittant misfire on #2.
 
what brand MAF did you buy? was it reman or new?

Also, if for whatever reason, you can get a brand new OEM DELPHI MAF, Part # AF10058, for 49.79 on rockauto.com
 


It was a Cardone Reman. I've never had any problems with them before, but I guess anything is possible. I don't think that this would have anything to do with the misfire though being that it was an existing problem prior to the replacement of the MAF.
 
You're going to need to verify that MAF in the boneyard is good and make sure that one is OEM and not aftermarket.

Yea test out another ICM. You could buy an ICM from the parts store and if it doesn't help, return it cleaned up. I like to call that renting parts lol.
 
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