2001 Chevy Malibu WOT power loss

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Engine pulls hard until about 3500 rpm then just stops pulling. Back off to about 1/3 throttle and it starts pulling again. I recently replaced the EGR valve. No trouble codes at this time. Starts and runs fine, drives fine as long as you don't go past about 1/3 pedal when revving high.

Not the transmission. I can hold a gear and wiggle the accelerator and feel the power come and go.

Anybody seen this before?
 
Check the condition of the catalytic converter, might be plugged. Check the temperature of the exhaust pipe before and after the converter , good converter will be 30-100 degrees hotter after the converter.
 
Doesn't feel like a misfire and I'm not getting any misfire or cat codes. I will check the cat with a infrared thermometer when I have a chance, and I'll pull the plugs I can get to. I dunno if I can get to the back 3 without pulling the intake manifold.

On a V6 1 cylinder would be 16.67% power loss
 
Oh I thought this was an ecotec 4 cylinder.
If its a V6, it has the coilpack waste-spark ignition. If a coil is bad you'd lose 2 cylinders.
Theres a couple reasons why it may not pop a miss fire code.

1.Its at a higher RPM. It may need a better understanding of the engine. You said you replaced the EGR. Did you reset the computer? IF so it may need to learn the engine more.

2. Its not missing at low rpm. It takes significantly less power to spark in a low rpm situation. To help it, the computer may also be hitting the spark 2 or 3 times each time the piston comes up. If the first spark doesnt jump, maybe the next one will and so forth. There is no time at higher rpm to be able to do multiple spark per cycle.

3. On some vehicles, the miss % has to be really high, 20-30% of all events in order to trigger a code.
 
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It actually might be the cat. It's setting a P0401 insufficient EGR flow detected. A bit of googling, and I find that a clogged cat/high back pressure can cause this code. So next weekend I get to drown bolts in PB blaster and pray, swear and bash knuckles trying to get the thing off. I don't have an oxyacetylene torch so the easy way is out.
 
So wait... you just replaced the EGR and its throwing an EGR code?

New Part Defective?
 
I also smell a cat problem. It's wierd the EGR code is for "insufficient" but whatever. You could have cooked stuff with all the backpressure.
 
EGR problems can be felt at the time you describe. If it's vacuum operated they usually bypass the vacuum until you're cruising along and putting some power into the pedal.

A plugged cat can also cause similar problems.

Since you have a code for EGR that's where you should start, before going for the plugged cat since that could be considerably more hairy if you don't have a torch. What's indisputable is that the code was triggered and the code in the computer has a specific set of criteria that triggers it. You also recently touched the EGR valve, so there's the fact that something was wrong before with it (or at least you thought there was), that you replaced it and might have even made a mistake. This may not be a coincidence, usually areas where things are touched deserve a higher priority. Go back and see if the EGR system is good and check the valve operation. If none of those pan out, maybe the cat is blocked and the backflow is causing disturbances in the EGR since it routes exhaust gases.

If you had a service manual that shows you the diagnostics for that code it would be even better.
 
The other EGR valve was bad and throwing a stuck closed code. I tested the valve before replacement. I'll look at the EGR ports but a clogged cat makes more sense to me with the power loss vs not enough EGR flow.

It makes sense to me. LIM leak, poisons cat, clogs up.

I'm going to run a coathanger through the EGR ports but I don't expect to hit anything.
 
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Originally Posted By: NoNameJoe
EGR problems can be felt at the time you describe. If it's vacuum operated they usually bypass the vacuum until you're cruising along and putting some power into the pedal.

A plugged cat can also cause similar problems.

Since you have a code for EGR that's where you should start, before going for the plugged cat since that could be considerably more hairy if you don't have a torch. What's indisputable is that the code was triggered and the code in the computer has a specific set of criteria that triggers it. You also recently touched the EGR valve, so there's the fact that something was wrong before with it (or at least you thought there was), that you replaced it and might have even made a mistake. This may not be a coincidence, usually areas where things are touched deserve a higher priority. Go back and see if the EGR system is good and check the valve operation. If none of those pan out, maybe the cat is blocked and the backflow is causing disturbances in the EGR since it routes exhaust gases.

If you had a service manual that shows you the diagnostics for that code it would be even better.


Not vacuum. Electronic solenoid with integrated position sensor.
 
UPDATE

I cleaned the EGR port. Trying to upload pics. It was plugged good and proper

I reset the computer, put it all back together and got the same exact behavior. Light throttle will run into 4500 rpm. Push more and you start slowing back down. Engine sound changes too, has a more farty sound to it.

I don't think the cat is plugged, it is welded in so that will be more involved to test. This seems more like a fuel/timing thing from the way the pedal responds. Knock sensor maybe?



 
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Originally Posted By: Thax
Check the condition of the catalytic converter, might be plugged. Check the temperature of the exhaust pipe before and after the converter , good converter will be 30-100 degrees hotter after the converter.

Use a vacuum gauge, very quick and easy.
 
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Originally Posted By: Lubener
Originally Posted By: Thax
Check the condition of the catalytic converter, might be plugged. Check the temperature of the exhaust pipe before and after the converter , good converter will be 30-100 degrees hotter after the converter.

Use a vacuum gauge, very quick and easy.


And if the cat is good?
 
When you go to pull out in traffic and the power takes a dump at half throttle and you start slowing down it is kind of hazardous. The high rpm is simply for testing purposes.
 
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