Newbie with cylinder 5 misfire.

**jmalm321** · 12-14-2009

Hello everyone, I am new to the forum and am having a hard time figuring out my problem. I have a 1999 GTP and i keep getting error code P0305, which is cylinder 5 misfire. I changed the plug, wire, coil pack and fuel injector. Before i changed the fuel injector the car was very sluggish and could not accelerate like it had previously.This was almost an overnight thing. When I would put the car at WOT and it would just chug along and stay in low RPM's. The boost gauge on the display pannel would also go to the max. After changing the cylinder 5 fuel injector the car runs better, but it still sets off the SES light which is from the P0305 code. I can also tell its still not as quick as it used to be. Also now the boost gauge doesn't ever go up, even at WOT. At least now though the car will go into high RPM's when i hammer down on the gas. The only mods i have are U-bend delete with cat and resonator removal, 180 t-stat and a CAI. I dont know if the recent cold has something to do with it?? Seeing as i live in MN. I also dont believe its a head gasket because there is not hissing from that cylinder and there in no coolant in the oil. Could it possibly be my PCM going out? Any suggestions would be greatly appreciated.

**minichopper6hp** · 12-14-2009

Do a compression test on that cylinder and let us know the results.

**jmalm321** · 12-14-2009

alright will do today.

**Swash** · 12-14-2009

Welcome aboard. First - when you pulled the plug - was the electrode damaged/bent at all? If so, it's an indication of a bigger issue. If not, then the next thing I would check is the coil pack, see if you can find someone near you that would be willing to swap out one of theirs to test. It is worth removing that coil pack to make sure that the connector on the bottom isn't corroded at all, either...it does happen.

As for the boost gauge no longer working - chances are that you either damaged or loosened one of the vacuum connections. The first (and by far and away the most common) place to check is the "T" connector that is under the SC snout. It's notorious for breaking. If not there, then trace the hoses from each end and inspect along the way.

HTH

-Swash

**minichopper6hp** · 12-14-2009

He said in the OP that he changed all of that so i would do a compression test and go from there.

**jmalm321** · 12-14-2009

ok so i did a pressure test on cylinder 5 and it was 120 psi. Is that where it should be? So now what could be a cause of this misfire? As for the connection there is a loose one, i just dont know where it is supposed to go. Its the one coming off the "T" under the SC snout. Of the two lines its the one farther away from you if you are standing at the front of the car looking at the engine. The one end is connected to the "T" but the other end is just hanging loose not connected. Where is that end supposed to go? All your comments are appreciated. Thanks in advance.

**jmalm321** · 12-14-2009

Oh also Swash as for the spark plug i replaced on cylinder 5, there was nothing wrong with it. It almost looked brand new. I think the previous owner changed the plugs and wires right before selling me the car.

**NaturallySmashed** · 12-14-2009

hmm idk why you wouldn't be getting anything on the boost gauge now.. take ICM and PCM out and get them tested.. as for the boost gauge.. idk? make sure the connections are good with the gauge and that you didn't move anything when you were changing the injector.

**jmalm321** · 12-14-2009

I know one of the vaccum connections isn't attached i just dont know where it goes. I described in the post above ^^^ As for the ICM or PCM, how would i test these? And could these cause this cylinder 5 to misfire?

**GTPJOE90** · 12-14-2009

theres a vaccum line behind the blower by the firewall check there or the T under the snout and the T on the fuel rail on the front of the blower.

**jmalm321** · 12-15-2009

ok so i figure out the vaccum line problem

After fixing that i took it out for a spin to make sure it was working and it did. Still having the misfire though when giving it more then half throttle maybe a little more. I also just remembered today that when i hit my Traction Control button it does nothing. I dont know if that may also indicate my PCM is bad or going out? I dont know how to test the Ignition Control Module either??

**NaturallySmashed** · 12-16-2009

you take them out of the car and bring them to advaned auto. i'm sure there's an autozone by you, ask them if they can test your PCM or ICM.. they can probably do both. (i know advanced can do both)

**badbrad** · 12-16-2009

eewwww. u gotta check all the vacuum hoses and connectors. try just 1 more wire. my car will missfire, most of mine was due to poor quality gas. i can fill with chevron and it'll run great a short time later. good luck and welcome. get a dvm and check resistance in primary and 2ndary side of coils. welcome!

**jmalm321** · 12-16-2009

Ok so i went to Autozone today and had the ICM tested and it tested out good. I also pulled the plug from cylinder 5 to physically see the spark, and there was spark. So now I need to either get my PCM tested or get a new one, correct? As for poor quality gas, I have filled up at the same gas station the past 4 or 5 fill ups, always with premium.

**badbrad** · 12-17-2009

can u check the coils?. i understand that its firing, but just questioning the strength of the spark. inside a haynes or chilton manual, it'll tell u how to check 2nd ary and primary side of coil. the place where "i" bought fuel was my problem with mine. rarely, i'd have a random misfire. buy some the correct cleaner and spray the maf sensor.

**jmalm321** · 12-29-2009

Ok problem was resolved. I brought the car into the local shop and had it diagnosed. The problem on cylinder 5 was that there was carbon build up on the plug and wire causing the misfire. The shop told me the reason for this was not changing the plug and wire at the same time, which was true. So all this for stupid plugs and wire. I'm a little mad at myself. oh well, thank you everyone for all your help!