I've got a car that I'm having problems with. It's a '98 Camaro Z28, bone stock besides exhaust. In closed loop the car runs like crap, has no power at all, and is throwing a MAF sensor performance code and right/left bank lean codes. No misfires, KR etc.

I start logging, and the O2s seem low, in the 100s at idle but occasionally bounce and hold 600-700 for a bit then drop back down, could instantly here the car run better/worse when the O2s would switch between 100s and 600-700mv. LTFTs are at 23 to 25%. Around 3.0 to 4.0 at idle for injector pulse width, and 10.0 under WOT. Under throttle, the O2s completely flatline to 0 to 50mv and the car had no power whatsoever.

I unplug the maf, and the O2s read a bit better, and car is a lot more responsive now but it still quite a bit down on power. I then command open loop and clear the fuel trims, and the car runs great. O2s go up to 900~920mv under WOT. But as soon as I go back to closed loop, everything goes haywire again and LTFTs take a dive to about -15% almost instantly.

Being that the car runs great in open loop, I'm contributing this to be a problem with a sensor somewhere, but which one? My first guess is that the MAF is toast. Before I started logging, I figured the O2s were gone, but they seem to be responding great, and show good readings under open loop. IAT was where it should be at.

I'm also including 4 logs. I know they are quick runs, but they should show everything that was causing any problems.

The first run is with nothing touched. Closed loop etc. There is a short run up to 50mph towards the end of the run with the O2s almost at 0mv.

The 2nd run is also with nothing touched, but TPS % is added to the log.

3rd run is with open loop commanded and fuel trims reset..

4th run is with the MAF unplugged, nothing else touched.

If anyone has any input, it would be greatly appreciated!

 

Does the MAF show lbs/min and frequency in the scanner?

Chart it and see if the graph goes up kinda smooth as you give it gas in park/neutral up to 4k rpms.

Could be a bad MAF and or bad O2's

When in closed loop, what Fuel Trim Cell are you in?

 

My car did the same thing when my MAF got dirty (from oil coming off the stupid fram airhog filter)...wouldn't want to run with the MAF but still loved open loop SD. If you haven't tried cleaning your MAF with either q-tips and rubbing alcohol or electronic parts cleaner, I would suggest it if you haven't ruled that out as a possibility of being the culprit yet.

Or like Billiumss said, it could be a bad MAF altogether, or any other problem.

 

Sounds like the maf and o2's are shot. Before you start replacing parts make sure you check all connections for damaged wires, blown fuses ect. If that checks out the 20 to 1+ afr at WOT and bad all around driving conditions are probably directly related to your maf reading very low, its either over oiled or has gone out. And they can go out, mine went out last year but all it did was throw an ses light.

If it still runs like crap in closed loop with no maf and the fuel trims go haywire i'd say your looking at bad o2 sensors. How many miles are on the car?

Another thing to consider after runing that lean under wot would be plug condition. I'd pull a few and see how bad they look, once the fuel was back in line at wot this could also account for the presistant lack of power issue.