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Good ole' P0304

L36 Killer

L36 Killer

New member
I own a 2002 grand Prix GT with 138,000 mi. recently started to upgrade the car's suspension and engine. K&N CAI, SLP headers, Hi-flow CAT, SLP exhaust, and just installed my Overkill PCM. The PCM got rid of the P0420 code but is now showing a P0304. New plugs and plug wires were installed about a month ago, along with new intake manifold gaskets, at a local shop. Have also cleaned the MAF.I am noticing a clicking noise from the area of the #4 cylinder at cold idle and when throttle is applied. one mechanic thinks it is a faulty lifter, that the lifter is collapsing when the oil pressure increases. I am going to start trouble shooting tommorrow after work, but I wanted to get some opinions first. thanks!!
 


i found a couple of other threads with the same problem, so I'll follow thier progress. Thanks for the advice though!!
 
UPDATE I checked the plug (found out that the friggin shop I had the tune up done at put in Platinum instead of Iridium like I asked for!) swapped the plug to a different cylinder-no change. Swapped the plug wires-no change. Then I tested the cylinder compression- best reading I got was 75lbs. and it never held pressure. Needless to say, I am stunned. Any thoughts on the cause and a fix would be appreciated. I'm guessing it's either a bad ring or a cracked block. It does run well though, no stumbling or stalls, just that rattling from the back valve train. I don't wanna scrap this car unless I ABSOLUTELY HAVE TO.
 
Well the plot thickens...I drove my car home tonight and noticed that the SES light was not on. So now my question is-if my #4 cylinder is as bad as that compression test said, why would the SES light shut off? Any ideas?
 
Wow, you are having problems. If you're having a problem on cylinder 4 with compression it could be a number of different things. Due to the mileage, I'd say it is more than likely valvetrain related. These engine don't have ring or block issues. The next course of action should be a cylinder leakdown test to determine if you have faulty sealing of the rings, valves, etc. Air out of the intake indicates intakes valve, exhaust is exhaust valve, oil cap is rings, radiator is blown head gasket. Make sure you do the test cold and again with the engine at operating temp. This test can be performed cold only, but best results are from doing it twice as the expansion of the different components may yield different results.

If the car thought the problem was gone after three consecutive drive cycles, the light will turn off. That's about it on that one. LOL
 


I'm going to perform my own compression test tommorrow after I pickup a test kit. Just to be sure...then I'll lookup how to perform a cylinder leakdown test and get on that this weekend. Thanks J !
 
bayus2972 said:
I'm going to perform my own compression test tommorrow after I pickup a test kit. Just to be sure...then I'll lookup how to perform a cylinder leakdown test and get on that this weekend. Thanks J !
Click to expand...

Cylinder leakdown test requires an air compressor. That's its downfall. Also, if you get a tester from Harbor Freight, be warned it only tests at 50 PSI...not high enough pressure to catch some leaks.
 
I have an air compressor, albeit a small one. How many PSI do I need to put into the cylinder? I was going to pickup a tester kit from Autozone.
 


I finished the compression test. Cylinders 2,3, & 5 read 160 psi. Cylinder 4 read 140 psi. MUCH better than the last test. I used a new test kit this time rather than the old (and obviously faulty) kit at the hobby shop. I noticed that both of my valve cover gaskets need replaced so I'll do them when I check the 2-4-6 valve train. Could it still be the piston rings? I am seriously (and HAPPILY) doubting that at this point. Doubting a head gasket as well with the test results for the #2 cylinder. So I am guessing that it is a worn or damaged valve, valve spring, valve seal, or lifter. Does this sound about right? Anything I am overlooking? My brother said to check and make sure that the oil ports to the valve train aren't gummed up or blocked.
 
As previously stated the odds of it being rings are slim to none I have never heard of anyone breaking rings on a stock N/A block before or at all for that matter. You would chunk a piston well before you would break a ring I am guessing. I would try the seamfoam and lean towards a sticky lifter or something in the valve train.
 
Removed the valve cover today (a minor victory for me!) Nothing really looks out of place. But TBH, don't really know what I am lookin for. Springs looked intact and in position. rocker arms didn't have any noticable damage. good amount of oil in the valleys. No sludge or heavy builup anywhere. Will try running compressed air into the cylinder at TDC and listen for any leak. More and more I am leaning towards the initial thought of bad lifter. Will DEFINATELY run seafoam through gas tank and oil after she is buttoned up. Thanks for all the replies :D!

SIDE NOTE- Last oil change I did (about two weeks ago) I switched to Royal Purple. That would have anything to do with this would it? I used to run with a high mileage synthetic blend.
 


Well, nothing showed from the compressed air in the cylinder other than a SLOW leak. So, I'm gonna clean a bunch of sht, paint some sht, polish some more sht, button her back up, and run the seafoam through her. If the seafoam can't get rid of that sound, I'll do a tear down and replace the lifters, upgrade the rods, rocker arms, and springs during my vacation. Maybe I can bribe hitman to give me a hand....:D

:th_peaceout:
 
:th_sick1:HOLY MOTHER OF GOD!!:th_sick1:
click

 
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