Code P0304

I upgraded my exhaust on a few days ago, and the morning after, I started my car and let it warm up while I loaded up for work. When I got in the car my SES was on.

Scanned and got two codes, both codes were P0304 - 'cylinder 4 misfire detected'. Cleard the codes and after about 300 mi the codes have not come back.

So, what could the problem be, The few things I have thought about are Plugs, wires, ignition module, coil packs, injectors, and/or faulty O2.
And, could the PCM have shorted and the codes be false? From what I understand a misfire, is a misfire. it would continue and I would get more codes.

A friend also told me that OBDII, after clearing codes, takes 100 mi in verification mode before it rescans. is that correct?

I recommend just keeping an eye on it and see if it re-occurs. If another misfire is detected, normally the SES light will flash then go steady and then store the DTC error code. The PCM does not need a drive or learning cycle to rescan for misfires.

Whenever you do an engine mod its a good idea to reset the PCM afterwards.

If the misfires problem continues around cylinder # 4 the spark plug or respective wire is the best starting point. Good luck!






http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

I agree with Bob, that the code could have been an anomaly and no true problem exists. If the code comes back, then you need to go through the steps to determine if it's fuel or ignition related.

I agree with bob as well.

Bnaylor and richtazz, Thanks for your replies. it has now been over 500 mi since i cleared the codes and no more have shown up so i'm going to write it off as an anomaly. My car has 90K on it so it's getting time to replace the plugs and cables anyway, I'll prolly do that when I upgrade the PCM in a few weeks. Do you have any tips on performing this procedure as I more than likely will upgrade to the Autolite 104's and MSD wires.

Bnaylor, when you said reset the computer after mods, are you talking about disconnecting the battery for a few minutes or clearing the codes or is there another procedure for a 'reset'?

I heard of if you did an off and on thing 30 times you can reset it. Bob--have you ever heard of anything like this?

I heard of if you did an off and on thing 30 times you can reset it. Bob--have you ever heard of anything like this?


It depends on the GM car model Andrew. Some you can disconnect the battery negative, some the positive for a while and it may clear DTC error codes and put the PCM into a re-learn mode. But it varies.

I use what I call the hot rodders trick and it works on "W" body cars. You disconnect the battery positive cable, then take the ignition to the engine start position and hold for at least 1 minute. (Of course, nothing will happen). Then take key back to off. The key will be stuck in the ignition and will not remove but thats not a problem at this point. Then reconnect battery positive and you will hear relays chatter. Next take key forward and then to off, it will remove at this point. Final step is to start the engine and then over a period of time the PCM will relearn.

Note: This procedure will clear an SES/CEL light, all stored DTC error codes and put the PCM into relearn to include driving habits for shift points.

I do this procedure everytime I do a significant mod. It works for me.





http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

Thank you sir. ike i said i heard about it from somebody at work but... How was the storm down there? did you get much rain or anything?

Thank you sir. ike i said i heard about it from somebody at work but... How was the storm down there? did you get much rain or anything?

We got some from the remnants of the one that hit Mexico. Nothing from Rita. Now we got hit with that cold front from the North and temps dropped to low of 50 from 90 degrees. It's either shake or bake here. Nice and refreshing. Don't have to worry about the cars overheating until next summer...lol. :lol2:







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

Very true.lol

aight, I think i did it right. we'll see how things go. thanks to bnaylor, ripn, richtazz and everyone else who has helped out on this.