Ok, here is a no BS diagnosis. Clogged CAT. How do I know? I had a 2001 Camaro that did this EXACT same thing. And I mean exact. I changed everything else first before I found it. I changed wires, plugs, coils, ignition plate, MAF and filter. Nothing fixed it. I was lucky and was under 80k miles so GM replaced it for free.

But, to check if the CAT is clogged you can try this. At night start the car outside and let it run for awhile, and I mean a long while. Crawl under the car and look at the CAT. If it's clogged it should be a slight red color, or maybe even glowing depending on the clog.

 

wouldn't taking the o2 sensor out alleviate any pressure on the cat when the exhaust escaped through that hole instead. As I suspected maybe the cat was bad, I removed the o2 sensor and it ran the same with that much less backpressure. I'll run it and see if the cat gets red

 

thats the same problems im having with my 01 monte, but in park it revs up fine as soon as i put it in drive it wont go over 2500 rpm i also changed wires,plugs and egr and still the same I also thoght it was my cat so ill have it remove today ill let u know if it fixes the problem so ill keep up with ur post

 

If your cars are under 80k miles take it to the dealer. I'm 95% possitive it's a clogged cat. If it is and the car is under 80k the dealer has to fix it because of it having a bad emission control system. It's 09 right now which makes an 01 8 years old. The emissions warranty is 80k or 8 years. Might wanna jump on it and see if they can do it.

 

i just had my cat removed and the car is running like a champ the guy said the reason for the codes is cus the heat is coming back up instead of out the back so try that and hopefully it runs better and thanks to everyone who posted it help me alot and saved me money too

 

I checked the possibility of a cat problem already and it's been ruled out.

Also my car doesn't rev past 2500 in park, let alone drive

I'm now more leaning towards bad fuel injectors or loss of compression.

The fuel trim readings on bank 1 are good almost 0% so they're running at near stock, while the fuel trim readings of bank 3 at at 50% on short term and long term since the most recent closed loop run.

This leans me towards a problem with 1 half the engine.

 

Ok the egr system is fixed, I ran a test drive and the I/M monitor says EGR system OK. On my test drive I had no codes but many symptoms. I got out on the road and took off gradually like the GM OBD II drive cycle says, Got up to 55mph and put on cruise control and drove 4 miles or so at 58 mph. I then gradually decellerated down to 20 mph, turned around and this time applied about 3/4 throttle and it was misfiring badly in the 2.5k-3k range, never got higher than that. I then got up to 55mph and re-equipped cruise control, it went a little bit, then it bucked alittle bit, kicking cruise control off. I traveled back to my house then cruised down to a stop at my driveway. It bucked a few more times on the way in.

I noticed that went it bucks the tachometer goes from liek 2.5k rpm down to 2k then flucuates some more before the car stops bucking and missing and settles down to slowly resume acceleration again. any of these driving symtpoms help anyone diagnosing the source of my problems?

 

I would just like to put my vote on the cat and if you can unbolt it or spend the 200 and get a aftermarket high flow (cheaper then stock) mine had a issue like this at 4500rpm's same throttle issues you describe. also i noticed alot of shifting issues when under heavy acceleration.

 

How did you rule out the cat? If you tried what I said, it's not really a test. Just something you can try. Mine was clogged really bad and it still never turned red at all.

 

Pulling out an O2 sensor might not be enough to diagnose a bad cat. Like I said before even when I unbolted the exhaust flange on my dads car still wouldn't start. We replaced the cat anyway and it was fine.

Loss of compression won't give the kind of symptoms your having. Bad injectors may.

Does the scan tool you have say "Bank" or just "Fuel Trim 1", with no "bank". If i remember correctly 1,2 and 3 refer to idle, under load and cruise. That -45% means it is running rich so the comp is reducing the amount of time the injector is open, it is trying to lean it out.

Have you checked the vacuum? Or did like someone else mentioned and look underneath at night? Even an infrared thermometer can diagnose a bad cat by measuring the difference in temp between the inlet and outlet of the cat.

Numerous people here have mentioned a cat. We may all be wrong but I wouldn't be satisfied until you really check that cat.