bad random misfire after warmup

[andyd00]

Ok this has still been a problem for a long time and i have done all the checks and even had to replace the O2 sensor(3rd time) and u-bend(not my choice) Its still misfiring random cylinders under load.
Now its so bad it'l do it in neutral and can almost kill the engine. Still no engine light. But when the engine is cold, it runs fine and as fast as it can be.
When scanned there is no knock or anything when it missfires.
Anyone have a similiar problem yet?

[ghize]

I had this problem with my 90 GP and replaced the crankshaft position sensor. Cleared it right up.

[andyd00]

Its been replaced twice now.

[andyd00]

But now starting yesterday, it runns like its lacking poer. Oh and it smokes ou the exhaust when it missfires. Does that mean its running rich? Or is it the fuel isn't burning. But anyway when it lacks power. The intake makes a funny noise like its gasping for air. Then when i give it alittle more gass the noise goes away and the power comes back.

[andyd00]

Well I had my local mechanic look at it and the fuel pressure looks fine until I revved it up a few times and hten the fuel pressure began to fluctuate by 2 pounds at idle. So we pulled off the vaccum hose to it and it kept doing it. So we think its the fuel pump. I hope it is, I'm tired of chasing this gremilin.

[ghize]

Have you checked your coils? Easier to change than a fuel pump. You need to check for resistance between the poles. I forget the exact numbers, but I want to say around 600 ohms.

[andyd00]

Originally Posted by ghize

Have you checked your coils? Easier to change than a fuel pump. You need to check for resistance between the poles. I forget the exact numbers, but I want to say around 600 ohms.

I didn't check them myself, but i took the coils and the iginition module out and had tested at autozone. I alos took a set from my freinds gtp and tried them on mine and nothing fixed it.



From what I understand, isn't the fuel pump for the gtp a two stage.

Maybe the second stage for the boost is gone.

Also I noticed the other day there is a nasty humming sound coming from the back when the car lacks power.

[GTPWarrior]

Change the coils. Thats what I had to do and it cleared right up.

[andyd00]

Ok the pump didn't fix it. And the fuel pressure still fluctuates even without the vaccuum hose.

But I found what is causing the missfire. I found an article saying to not use anyother spark plug wires except from GM. Went to the dealership, 60 dollars later missfire fixed. DO NOT BUY AUTOZONE WIRES-NOT EVEN PREMIUM WIRES.

But there still is a problem with power, I'll place new post.

[GTPWarrior]

So very untrue for anyone with a 98 GTP. I have them (autozone wires) and Have had NO problems at all.

[andyd00]

Originally Posted by GTPWarrior

So very untrue for anyone with a 98 GTP. I have them (autozone wires) and Have had NO problems at all.

Well maybe its just the 99's with the prob. Anyway, when I was searching for 8mm wires, I found an article with a 99 gtp that tried three different types and all of them failed within days. It sounded like mine and the author said he just put the originals back and and no more probs.

[GTPWarrior]

Yeah but If I am not mistaken are they not the same engine? Maybe he had mods. I haven't really started moding mine out yet. I would still check out your coil packs. those you can meter out just in case. Let me know what you find out about you loss of power. If we have the ssame symptoms and from what I have read I am thinking it has something to do with the KR and /or timing.

[Faze2183]

sounds like the coils

[GTPWarrior]

Loss of power?
Mine are brand new

[kustomkid54]

Want an "old mans" thoughts? Check the ICM. By the sounds of it, you could be fireing two cy. at a time. Take it up to Auto Zone and have it scanned. Will more then likely come up with a random misfire. It's just my thoughts. But you have to stop throwing parts at it. The cost has got to be getting high. Good luck