Thread: 01 GrandPrix GT random missfire?

I have a 2001 GT with an random missfire. So far the scanner has recorded missfires in 2345 cyls. But not consistantly. It only happens when the engine is under a load. It will not happen in neutral, park, or power braking. Primarily during acceleration especially up hills and going to pass.

I have changed the plugs and wires with good delco equipment. This afternoon I am going to swap coil packs and ignition modules to see if that fixes. Then I am going to ohm test the injectors to see if that is the problem. If it isn't either of those I will test crank shaft position sensor.

From there I have no idea where to go or what to check.

Any ideas?

It is not the coil packs or ignition module. I replaced with a known working set and it still miss fires just like before. I also checked the MAF and it looks fine.

I have tested 3 of the connectors to injectors, to make sure a signal was being sent and they were fine. I ran out of time on my lunch break and will check the other 3 this afternoon.

Can you test a CPK to make sure it is functioning properly?

Can you check the EGR Valve as well?

Ok so here is what is going on with this car plus a little background. 2001 GT
Car has 89k had 71k when we bought it about 2 years ago.
Up to last november I had replaced fuel filter, PS pump, alternator, and front brakes. Nothing too major. Then on our way home from Thanksgiving the transmission goes out. This is too early for problems with this tranny. I work at a tranny shop so we put an overhauled transmission in.

The car ran fine up until about 2 weeks ago when my wife(her car) began complaining about a shudder during acceleration. I took the car to work and hooked up the scanner.

No codes. I drove and watched the miss fire counter. The scanner recorded random miss fires in several cyls. So I replace plugs and wires, then drove. The shudder was still present.

Next I swapped coil packs and ignition modules with a known working set. The shudder continued.

Next I drove again using scan tool and recorded only one miss fire out of 3miles of driving. Shudder was still present.

Next, assuming the problem is still a miss fire and that the scanner is not picking it up, I checked the injectors as well as tested that a signal was being sent to the injectors from the computer. All was good.

Next I un hooked the EGR and drove, still a shudder.
Next I un hooked the MAF and drove, still a shudder.

I hooked up scan tool again and drove, the only codes were from when I drove the car with the EGR and MAF unplugged. Shudder is still present with no recorded miss fires.

I concluded that the miss fires were a seperate and unrelated issue to the shudder.

Today I drove and watched the TCC slip, thinking that it may be a transmission problem. And the converter showed excessive slip. However, I can not determine the cause.

If the TCC was bad it should set a code and shudder consistantly during when coming in and out of lock up.

It could either be a bad converter or low voltage being sent to the TCC causing it to slip in and out. It is possible that this is happening so fast that the computer fixes the problem before it can set a code.

So anybody want to buy a car?

Would it possibly be the catalytic converter? I'm currently having the same problem with my 2001 GT!

My 02 GT had the same issues, it was the catalytic converter, bring it to GM.