Car Still Lacks Power. Need Help!!!

[OSUCowboy27]

I have a 2001 with a 3.1L and 122,000 miles.

The Problem:

Idles fine and drives fine at very slow speeds (< 10 mph) but if I try to accelerate, the car will "bog down" and not take off. You can hear the throttle open (kind of like the secondaries on a 4 barrel). It does this no matter what gear I am in. There is also a very loud squeal / whine from the back of the motor. This may or may not be related and is not the alternator, PS pump, water pump or ac compressor.

The Attempted Diagnosis:

No codes. Fuel Pressure is 46 psi at idle and engine off. Fuel pressure is 56 psi at idle and vacuum hose off of fuel pressure regulator. No pressure bleed down. Fuel pump should be good. Injectors sound OK, nothing obvious. ECM checks out. Can't find any vacuum leaks (used unlit propane torch). EGR valve is new and should not be the problem.

The Attempted Fixes:

New AC Delco plugs and wires, new fuel and air filter, new pcv valve.

Possible Solutions:

Fuel pressure regulator?
Plugged or restricted Catalytic Converter?
Transmission?

I do not want to start throwing parts at it. I figure if a coil or injector was bad a code would be stored as to which cylinder was affected. Any help would be greatly appreciated.

[GTP Dad]

I would start with the cat. Since the engine seems to run properly then you may have an exhaust issue in that the cat is blocked. I would remove the pipe in front of the cat to see what happens. If the cat is blocked the performance should increase if not then the problem lies elsewhere. The loud squeel could be the serpentine belt squealing and this could be due to either a loose belt or a bad tensioner. They are not expensive. Finally, if you eliminate the above issues two other possibilities. 1. Bad torque convertor/transmission or a power steering pump that is draging the engine down due to it being ready to lock up. (could account for the squeal) Try the cat first and go from there. Post your results and if nothing works we will try to help find out what is going on here.

[OSUCowboy27]

I took the belt off so no accesories are turning and started it and put it in drive and gave it the gas with foot on brake and it started acting up at higher rpms and there was still a loud squeal. I really think it is the converter.

[BNaylor]

I vote CAT convertor. GM put out notice that 2001 - 2002 Grand Prixs and other GM "W" body cars were possibly delivered with a bad CAT where the end cone breaks off and causes the convertor to clog. Symptoms were MIL light or lack of power. It was more applicable to the GM cars with the 3800 and 3400 engines but from what I understand may be applicable to the GPs with 3100 too. A few owners with the 3100 that posted on this forum got their CATs replaced for free.

A clogged CAT can make a whistling or squealing sound due to the problem above or excessive exhaust backpressure. Contact Pontiac Customer Service or local dealer and see if you qualify.

Due to your mileage you may have problems because the warranty extension was good for 10 years or 120K miles, whichever comes first. But it doesn't hurt to try. You can get aftermarket CATs for well under $100. Good luck.

[OSUCowboy27]

Took it to a muffler shop and they did a back pressure test and it for sure was the converter. The cost was $330 installed today. He said it would have been $170 installed but there was something special about this like a bend in the pipe.

[BNaylor]

Originally Posted by OSUCowboy27

Took it to a muffler shop and they did a back pressure test and it for sure was the converter. The cost was $330 installed today. He said it would have been $170 installed but there was something special about this like a bend in the pipe.

Must be talking about the u-bend after the CAT but I don't see how that would justify a charge that high. The $170 is better. You can get a hi-flow CAT like a Magnaflow for around $55 and about $50 for installation. Is this an aftermarket or OEM GM CAT? It is your decision based on your circumstances. Good luck.

[OSUCowboy27]

I think the $330 included the backpressure and temperature testing, converter, instillation and taxes as well as getting it done today so it is worth not having to wait until next week. The converter has pipes and flanges on both ends with fittings for O2 sensors so there is more to it than just the converter. All things considered, it is a fair price.