1994 Z28 all stock other than headers and cold air. It shows on the wideband that it goes super lean when going to closed loop. It will flop in and out of open and closed. I took an idle log of it doing this. I've had this problem since I had the car. I have an open loop tune I'm thinking of using so the car can be drivin. It also has new Bosh O2s and it still runs like crap. checked for vacume leaks but none found. Here is a link to the datamaster file if somebody could please take a look. By the trims it looks like it's rich but the wideband says lean so I'm not sure what to do.
http://www.mediafire.com/?jkndgyzm5jh

 

Your o2 sensors are screwed up. If you graph the o2 sensor mv for the left and right side you can see that they are very slow to switch. Your pcm wants to see the o2 sensor bounce back and forth between 200-900mv very rapidly. Yours move and hang. Just my opinion, the pattern of the left o2 looks worse than the right, it never attempts to switch but does track rich/lean with the flip flopping into open and closed loop. Need to inspect your wiring harness if the car has new o2 sensors, what type of extensions are in the harness.. or has somebody extended the harness at home rather than buying extensions.

Your wideband is correct the car pulls loads of fuel out due to the crappy response of your o2 sensors and runs it lean.

Your maf airflow and everything else looks right on. The problem is either with the o2's themselves the harness or even the pcm circuit that controls and interprets the signal. Open loop is not a solution, its just a workaround to an issue rather than fixing it. You can very easily take whatever tune you are using now and make it full time open loop by changing one constant. Gas mileage is really going to suffer and if the maf gets dirty etc it will really run rich.

If you want any help making the current tune you have into full time open loop just to drive the car until you can get a chance to look it over closely just ask.

 

Thanks for your info. Yes the sensors are new. The extensions I have no idea what kind they are. They were on the car when I bought it. I just checked the wiring and it looks to be fine, nothing burned. I then checked to see if I was getting voltage down to the O2s and it is. I pulled the O2s out and they look black as hell. I do have another pcm I can try. Some people say that the Bosh O2s don't work very well but don't know if it's true. I have them in my LS1 cars and they seem to be fine. I have it flashed open loop now so it will run better. I would like to be able to fix this problem because of just what you said..mileage. though it was only getting about 13 before.

 

Its not unusual for o2's to be black as coal after some spirited driving. I would probably pull the extensions and do a resistance test on them. It may also be that the bosch sensors are not getting hot enough to function properly. Does your wideband read about what is commanded for open loop afr with the car warmed up at idle? Just to eliminate any possible issues with injectors etc.

13mpg is more of a statement about your driving style than anything . I don't like using mpg as any indication of tuneup unless the mpg is based on an entire tank of gas on the highway with the cruise control on.

 

I'll go out and check the extensions. The poor mileage is correct because it's not drivin by me. My wife drives it to work and she doesn't know what WOT is. haha

 

well I went through all the wiring. I checked the resistance from the O2 connectors back to the pin on the pcm. They are all fine. They also are both getting 12.5 volts. I then thought possibly the grounds for the sensors may not be working right so I ran new grounds for the O2s. None of that done anything so I then changed to my spare pcm and still the same. So I ruled out the pcm and all the wiring from the sensors all the way to the pcm. what else is left? Are the Bosch O2s just junk? I also sprayed around the intake and throttle body for air leaks and found nothing.

 

I had a built supercharged Grand Prix that absolutely hated Bosch O2 sensors. It would burn them out in 500 or so miles. Delphi ones would last several years. Not sure if this is your problem but may be worth a try.

 

Just more info that was said in post #2.. Pictures not the best, (left click on pic, view image, CLT+ to blow it up) but you can see the poor response and low voltage swing of your left O2 sensor. You could swap sensors left to right then do another log to see if problem follows sensor or wiring.