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Engine Power Loss at Higher RPM

G

GP Modder

New member
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
 


What have you done tune-up wise to it? For just over 100K miles I would be changing: Plugs, wires, air filter, fuel filter, trans. filter and fluid. Clean the MAF with approved MAF cleaner. Have you ever changed the LIM gaskets in the car?

A clogged cat comes to mind at that RPM. And yes, the P0102 Low MAF input can cause all sorts of issues. I'd remove it and clean it really well then see what you get.

Not sure what a P466 is.
 
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?
 
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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.
 


Bio248 said:
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.
Click to expand...

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.
 
GP Modder said:
Where is that o2 sensor located? Down pipe or monifold?
Click to expand...

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?
 
GP Modder said:
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?
Click to expand...

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.
 


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?
 
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.
 
^^This^^ The O2 sensor you are looking for is between cylinder 4 and 6. In fact, cyl. 6's plug wire is almost touching it. Not sure how many tools you have available, but it may be easier to just rock the motor forward and remove the O2 from the top. Never tried it, but it looks possible this way w/ a long enough extension.
 


You know me.
IMG_6611.jpg


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.
 
All gm 3.8's have this issue sooner or later in their lifespan.it happens most on the supercharged models but if your car hasnt had its tuneups at the right intervals it will plugg sooner.Take it to autozone and have them scan it.if it pulls back catalist insuffisency code(sometimes o2 codes will come up with this code} the cat is plugged.8/10 this ends up being the issue when low power is described see it all the time here at midas.You will want to do a full tune up with that cat to ensure your not burning excesive amounts of fuel. and check the both sides of the intake plentum(black plastic on top underneath gray 3.8 plastic cover.) as these are also known to develop internaly leaks into the combustion chambers.catch them early and you wont have to replace head gaskets or worse .motors!But back to the point.if that cat is plugged it got that way because something is wrong.weather it be the manifold gasket or bad plugs and wires.
 
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