Thread: still mifiring..

Hey guys my names josh. Posted on here a few times and looking for some help. I have a misfire on cylinder 3. I work at AutoZone and have put my code reader on my 1999 Gtp it says misfire on cylinder number three. I changed plugs and wires twice too verify they aren't bad. I did get the ac delco iridiums that it calls for. I checked my fuel pressure about a week ago and its two pounds low. I have had this problem for a while now. It only misfires when I give it over half throttle. I changed the fpr as well thinking maybe the diaphram was bad. And got a new high flow cat from zzp as well. Still no luck. I'm not thinking fuel pump because its only misfiring on cylinder 3. Any suggestions?
Thanks for any input guys it will be greatly appreciated.

Okay I will give it a shot but the thing is that I had a cyl 4 misfire before and the I changed plugs and wires and evthing was fine for about a month and now it jumped to three?

Yeah could be I guess. But it only misfires at high rpm.

okay guys so i tried injectors.. no luck. as for the coils, it used to be misfiring on four then i changed plugs and wires and problem went away for a bit. now its misfiring on 3 as i said and im just wondering how that could be the coil since cylinder three and four arent on the same coil pack. and the icm idea is a possibility but wouldnt that affect all the cylinders? hit me back.

thanks again for all the help and ideas guys.

Four is no longer missing. I honestly am thinking maybe the fact that 4 used to be missing has nothing to do with three missing now. Swapped the coil no difference as well guys. I'm taking icm into work tomorrow and testing it out. And no sir I don't run 93 octane. I run premium fuel. These cars take 93 octane? What?!! If that's what is I'm gunna freak out lol. Call me stupid if you want but I didn't know that.

So no 87? Run 89 octane and up?

Originally Posted by 99PGPGT

have you been running 87??

cuz i have never seen a gas station label 87 as "premium"....


also, if you have the aluminum dust boots over the plugs still, take them off.

What does that do taking off the aluminum boots? and also i too was using 87 and started using 93 and i noticed a difference.

Originally Posted by scottydoggs

those metal boots can cause misfires, sparks shoot off the boots to the manifolds.

Well i guess i know what im doing today.lol

Yes I do have the aluminum boots on. I will take them off thanks I forgot all about that. And my wife has put 87 in there recently. I will be sure to run higher octane fuel from now on. Good idea with those boots though. And another thing too I forgot too mention earlier ever once in a while it has a long crank start... Thanks again for all the help guys and appreciate everything you guys are doing for me.