Thread: Engine Power Loss at Higher RPM

Good Day, first time poster however been using the search function quite awhile.

I have a problem with my 2001 GP 3800 II that I can't quite figure out and am wondering if any of the GP gurus can help me with.

Basically the engine is loosing much of its power in the higher RPM range. Say 2500 RPM and higher, ie: when passing or climbing a large hill. The engine works fine below 2500 however when above that I can mash the pedal and no real increase in RPM or power. Real drag when passing a semi.

I originally thought that because the car has 180k km's that the transmission filter might be plugged and starving the torque converter for fluid, so the power wasn't getting through to the wheels. Changed the fluid and filter and no change. However I did notice the fluid was quite black and smelled a little burnt. That may be due to it never being changed as I purchased the car used so i have little history on what work was done on it.

I read the codes after this to see if it was engine related and I have P466 and p0102. The p0102 has been there awhile which created some engine hesitation when cold, but nothing like this.

Where do you guys think I should start? Would the MAF create this kind of an issue?

Thanks

The engine uses the maf to fuel itself. Try unplugging the maf and driving that way, is the power restored?

I have the summer past installed new plugs, wires and air filter. Put a new MAF in however it was a CarDone sensor which crapped out after two months. Fuel filter hasn't been done yet. Last weekend I done the transmission fluid and filter. I have not done the LIM gaskets yet.

I have another MAF from a 98 GP which I could install however the sensor is a different shape than the 2001 MAF. To install it I would have to change the entire throttle body. I have both if I thought it would work.

Whats a good way to check the cat?

I've tried unplugging the MAF but the driveability problems become much worse. With it plugged in there is some cold hesitation which goes away quickly, however with it unplugged its missing and surging all the time.

If CAT is plugged wouldn't it set a code for the CAT?

it may or may not set a code. if you unplug the upstream o2 sensor from it (yes, you'll be pouring exhaust out into the engine bay) should run better if the cat is causing a significant restriction.

Where is that o2 sensor located? Down pipe or monifold?

Originally Posted by Bio248

it may or may not set a code. if you unplug the upstream o2 sensor from it (yes, you'll be pouring exhaust out into the engine bay) should run better if the cat is causing a significant restriction.

What Bio said. Sounds like a clogged cat. Unplugging the O2 sensor will let you know for sure if the cat is clogged. My 02 gt was doing the exact same thing. Replaced the cat, problem fixed. Great time to replace the stock Cat with a Downpipe w/cat to delete the ubend. Better mileage, and a few extra HP, definitely worth doing it.

Oh and mine did not throw a code either.

Originally Posted by GP Modder

Where is that o2 sensor located? Down pipe or monifold?

Just unplug the one before the Cat in the Ubend. Fasten the 02 sensor somewhere out of the way so it doesn't get messed up. Go drive around and see if its better. Now that the gas can escape through the 02 sensor hole it will run better IF the cat is clogged. If it does run better, replace the cat. Again, I suggest buying a Down pipe with a cat so you can delete the restrictive Ubend. Wont cost you any more then just replacing the Cat.

If it still runs like ****, there is some other issue then a clogged cat.

Good luck !

I am going to try taking out the O2 this weekend and see what happens. I would like to do the DP upgrade, probably go really good with my SLP Cat back. I have a 98 available for parts with a working CAT on it, funds will determine if I use the scrap one or upgrade. Decisions decisions....

Is that front O2 hard to get at?

Originally Posted by GP Modder

I am going to try taking out the O2 this weekend and see what happens. I would like to do the DP upgrade, probably go really good with my SLP Cat back. I have a 98 available for parts with a working CAT on it, funds will determine if I use the scrap one or upgrade. Decisions decisions....

Is that front O2 hard to get at?

No its not hard to get at. Jack up the car and use the appropriate amount of stands to safely secure the vehicle. Then just before the Cat (toward the engine) there will be a U shaped bend in the exhaust. On the top of the U you will see your 02 Sensor. That is what needs to be removed and secured so you can test the cat. Be careful not to screw up the wiring when your unscrewing it. Fasten it somewhere and take it for a drive.

I would be surprised if that is not your problem. I had the exact same symptoms and it was a clogged cat. I also thought it was my transmission because it felt like it lost all of its power when accelerating into higher rpms.

This is actually what I replaced my bad cat with. Its essentially a downpipe with a magnaflow cat. ZZP sells downpipes with cats on them I think for a little cheaper but I didn't have time to wait for one. Got mine at O'reillys for like $199. Works great, car has never ran this good.

MagnaFlow Catalytic Converters - 49-STATE & CANADA Catalytic Converters For Trucks, Suv's, American Muscle, Diesel, & Sport Compact Vehicles

Thanks for the advise guys, gonna crawl under there this weekend...see what I can find and report back. That is a nice looking CAT, U bend delete too. The one you got from O'reillys did it have the U bend?

I was looking at a few photos and it appears the u bend O2 is after the CAT, can anyone confirm this?

the u-bend is definitely after the cat. you want to pull the upstream o2 sensor which is on the top/middle of the rear exhaust manifold.

You know me.


See the wire hanging on the left side...that's the O2 wire. If you stand on teh passenger side of the car and look down at the back exhaust..you'll see it.

Thanks again guys and certainly appriciate the photo Bill. Looks like fun to get at. I'm thinking a crows foot wrench and about 18inches of extensions should get to it...lol

I use this type of O2 socket (available at parts stores or Sears) Great deal on Schley 93750A at ToolTopia.com

Then say 10 or so inches of extension and the ratchet. You'll find it's easier to get out after the car has been running. Down side is...it'll also be hot. Put a work glove on and use the wire...the heat is more manageable that way.