2002 3.8L V6 -

A little backround first. A few months ago, out of nowhere my car started losing power. Over the course of two or more weeks, it got so bad that I couldn't go over 45 mph. I determined that one of my spark plug wires was bad, so I changed all of them and the car started driving great. Also around the same time I got a P0410 code - Secondary Air pump malfuntion. I ignored it because from what I read it doesn't cause drivabliltiy issues. I've been driving the car ever since, and the problem is starting to happen all over again, and if I'm on the expressway going about 50 or 60mph and I give the car more throttle the, there's a clanging noise coming from the engine - like bap bap bap bap, in rapid succession. The rpm's shoot up and the car doesn't go any faster. The plug wires appear to be fine. ANy ideas what's causing this?

Possible bad CAT converter. See advisory at link below.

Click here (http://www.automotiveforums.com/vbulletin/showthread.php?t=681283)

Also, what is the current mileage?

I think you may be right. That would explain the clanging noise, and plus when I'm going up a steep hill, I loose alot of power. It must be the fragments rolling to back of the cat blocking the pipe.

Just an educated guess. How many miles do you have for possible warranty purposes?

I had the same problem with my wifes 1999 GP a few years ago. At the same speeds but mostly from getting on the freeway from an on-ramp or trying to accelerate from 50-60 mph.

Turned out to be a valve in the transmission. I don't know which valve but perhaps the pros would have a better idea. It seems to be common. I know of another GP owner who had the same issue.

Cost at the dealer..if I remember correctly was in the $400 range.

Based on the OP's symptoms I would pursue the CAT converter avenue before looking into a possible autotransaxle issue that may not exist and due to the strict warranty limitations to get the work covered for free at the GM dealership. The major difference with any 2001-2002 models with SII 3800 engine versus the 1999 is the advisory issued by GM admitting to an issue with the CAT converter. As a matter of standard policy when a member posts a possible CAT issue with any 2001-2002 we always refer them to the advisory and recommend that course of action first.

GM's standard CAT warranty is 8 years or 80K miles, whichever comes first. For relevant 2001-2002 models the warranty was extended to 10 years or 120K miles, whichever comes first.

Just had the exact thing happen to my 99 gtp. It was a clogged cat converter.

Thank you so muich. I took it to the dealer and they confirmed that it was the Cat Converter. They replaced it free of charge and even gave me a ride to work while it was being fixed. Thanks again!

Why are there no codes popping up on these Cat issues? Other vehicles I worked on get Cat inificiancy codes or O2 sensor codes when the Cats get plugged. I am working on a 2001 Grand Prix right now with the loss of power at higher RPM issue. I am leaning toward the Cat being the problem, but no codes? The EGR tube burned a hole in the intake plenum, not where they usually do by the coolent area next to the throttle body, but straight up on the top from the EGR tube. This vehicle already had the Updated aluminum EGR tube in it, so it seems that the EGR was bypassing extra hot exhaust somehow. Could the CAT do this?

could it be carbin build up in the TB

I would guess the converter is blocked, and it burnt the hole it the top of the plenum because the exhaust gases had no where else to go but out the EGR stovepipe. I've never heard of this happening before, but I guess it could happen.

The EGR tube burned a hole in the intake plenum, not where they usually do by the coolent area next to the throttle body, but straight up on the top from the EGR tube.

the EXACT, yes, EXACT same thing happened to me. mine got so bad it caused a p0171 code, engine running too lean (vacuum leak obviously) the only thing the shop could think what caused that was too much backpressure from a bad cat. my cat tested as good as new so they/we just assumed the previous owner let the cat get way too bad

I am changing the CAT no matter what. Another GM mechanic has suggested that a bad/leaking fuel pressure regulator could cause this hole to burn through. If the regulator was to leak into the vacum than get sucked into the intake plenum chamber, he says that the exhause coming out of the EGR tube could act like a blow torch and burn the hole. I am not sure if I buy into this theory, and a regulator is not a cheap item to just throw on. Does anyone else think this may be a possibility?

Wondering if BNaylor could chime in on this issue also, thanks

I am changing the CAT no matter what. Another GM mechanic has suggested that a bad/leaking fuel pressure regulator could cause this hole to burn through. If the regulator was to leak into the vacum than get sucked into the intake plenum chamber, he says that the exhause coming out of the EGR tube could act like a blow torch and burn the hole. I am not sure if I buy into this theory, and a regulator is not a cheap item to just throw on. Does anyone else think this may be a possibility?


The vacuum supply for the FPR is at the throttle body, so IMO normal EGR flow is not sufficient to cause any kind of "blow torch" effect on the leaking raw fuel. This would be more likely to cause a UIM explosion if the raw fuel were to get ignited in the manifold. The only thing I can think of that would cause such a rise in EGR flow and temperature as to burn a hole through the UIM is a blocked converter or other exhaust restriction.

I agree with Rich.

Plus you can test the fuel pressure regulator to see if it is regulating properly and also pull the vacuum hose going to the throttle body and check for possible raw fuel due to a ruptured diaphragm which is possible but not that common.

I would go with a CAT converter since if defective the internal CAT temperatures can rise dramatically and the effect may be seen when the EGR is called active by the PCM and hot exhaust gases (more than normal) are injected back into the UIM.

Had GM warranty the CAT, we are at 118,000 and the warranty went to 120,000, no arguements from them on if it was covered or not. Anyway the CAT replacement did the trick on the loss of power and hopefully it was completely responsible for the hole burned through the plenum, might change that FPR anyway just to be safe. Thanks for all the input.

You're welcome sunspot, and thank you for the feedback. Letting us know your problem was resolved may help someone else reading this thread with the same problem.