I've been trying to get my car running well again after it has been sitting for about 2 years. I had developed some minor issues during this time. So far I've replaced the O2 sensors with new Delco units and spark plugs with NGK TR6 plugs. Opti seems fine and my problem seems to be fuel related.

There is more info on my past problem in this thread https://www.camaroz28.com/forums/sho...ht=WOT+Stumble

Since that problem I have replaced the O2 sensor (now I have two new Delco O2 sensors that are functioning) that was bad and have driven the car about 400 miles. Most of these miles were HWY miles with little or no aggressive driving, just cruising. During this time I had monitored the O2 sensors and fuel trims to make sure everything was OK, which it was.

Today I was on a back road with no traffic and was doing some WOT runs from a stop thru 4th gear, a 1/4 mile run pretty much. I had done about 3 of these in 4-5 minutes. Immediately afterwards I continued driving down the road at 55MPH and noticed the car was starting to miss/stumble under light load. I drove the car home which was about 15 miles away. I shut the car off for about 25 minutes and then grabbed my Snap-On scanner and went for another drive to check into the stumble. Drove for 30 minutes at regular speeds, not WOT or aggressive driving. The car drove fine, no stumbling or missing at all.

I then drove to an area where I could do some 1/4 mile runs to see if the stumble would return, this time with the scanner. I did 3 runs just like I had done in the previous drive, with the same missing/stumbling results again. I checked the O2 readings and they seemed to be frozen in place. Normally they are reading high/low very quickly. Now the readings on both bank 1 and 2 were moving very little. Short term fuel trims were split very badly, 110/205 and the injector pulse width showed this as well. Long term fuel trims looked good, 132/136.

I pulled the car over and shut it off and let it sit for 5 minutes. Started the car and drove it normally down the road checking the O2's and fuel trims. Now everything was back to normal, O2's reading good, Short term fuel trims were at 134/133 and injector pulse widths readings were even between banks.

I repeated this same sequence of events two more time with the same results. The car would begin to stumble/miss after the WOT runs and would go away when shutting the engine off for about 5 minutes.

I have no idea where to look, the car drives very smooth with no stalling what so even until after I do WOT runs, it runs very well at WOT.

Is it possible that the TR6 plugs are too cold for my setup causing the O2's to foul when the engine is at WOT? I've been running the same tune for 5 years and it has been fine. The only thing I have changed recently is the O2's and spark plugs.

Looking for any help or a direction to start looking.

 

Have you changed the fuel filter after sitting for 2 years?
What about a good fuel system cleaner?

Have you looked at the fuel pressure during the problem?

 

No I have not checked the fuel filter or pressure. That is at the top of my list right now, a buddy is letting me use his Fuel Pressure tester and I'll put in a new filter to eliminate that. Thanks for the help.

 

Not saying its your problem or not but, when I first got my z28 it was doing something similar. Turned out it was a faulty egr valve. It would drive fine but, after a wot pull it would run like crap. Even if its not throwing a code, you should still test it.

 

The car is EGR and AIR delete, thanks for the suggestion though. Back when I did have my EGR it caused problems so it was removed.

Right now I'm going to check fuel pressure and filter, if that checks out OK I'm going to stick the NGK TR55 plugs back in, maybe the TR6 plugs are giving me the problem.

 

Any update. It's been a week now?????