My 94 Z28 seems to have a problem. It's always been like this. It has headers other than that stock. First start in open loop is fine from what the wideband says but then right when it switches to closed loop the car will start to stumble and the wideband will flatline off the chart on the lean side. Over 18 to 1. Then it will throw it back in to open loop and the AFR will return to the normal open loop AFR. Then switch back to closed and do the same thing. I replaced both O2s thinking that was the problem but it didn't help. I also checked to make sure it had voltage to the O2s for the heaters and that's fine. no exhaust leaks either. MAF is idling around 7 gr per second so that's fine. No code either. I have tunercats so for now I just run it in open loop and changed the MAF tables so it wasn't so rich but would like to run the O2s. Anybody have any ideas? The original tune was stock other than fan settings and spedo and smog crap turned off. Is there a table I can change to give it more fuel in closed loop?

 

If it's the '94 can you download TTS DataMaster EE (good for 20 free logs) and get a trace. If it's switching back and forth between open/closed loop it would be interesting to see what is causing it. My guess is something is wrong with one of your O2 circuits causing BLM ready to drop out. (burnt wire, bad splice, heater dropping out intermittently, PCM, etc). The lean in closed loop also points to an O2 problem. In Closed loop the PCM is going to read the O2 feedback as gospel and adjust the fuel to what the O2's are saying. If they are incorrect, as it looks here, you AFR will be incorrect, there is no way to fool the PCM and change what it thinks. If yo change MAF tables then the PCM will eventually compensate and mess up the AFR again. Get a DataMaster trace and see what the actual O2 voltage looks like would be my first recommendation.

 

If the headers were coated and you never changed o2's after running the headers in the ceramic coating will eff the o2 sensors up and make the response horrible. Unfortunately I dont believe there is a code in the obd1 pcm for slow response from the o2's just codes that kick it into open loop once it hits the limit on long term and short term fueling. So if you can scan it and watch the o2 trace in datamaster you may be able to confirm that is the issue once you see that the o2's arent oscilating and the blm is just dropping like a rock when you hit closed loop.

 

yea I heard that about those headers. I did have them go bad so I replaced both sensors. I just ran an idle log using datamaster to show how it flops in and out of closed loop. I'm tryin to figure out how to save the log in datamaster. It's alot diferent than EFI Live that I'm used to. Does it save it as a text or something? I thought I had it saved to a text but then the text just looks like a scrambled up mess of letters and numbers..

 

It saves it to a datamaster file or .uni

You can then export channels from the datamaster file into a .csv file which you can open in exel and view like a spreadsheet.

 

Where is your wideband sensor located, relative to the stock narrow band sensors?

 

back about 3 inched on the opposite side of the header

 

Opposite side of the "collector"? And you are only monitoring one bank with the wide band?

 

yea that's how we do it on LS1 cars also . usually in drivers side header for LS1 cars since that side usually run leaner.figured I could monitor my LT1 the same way. I know the wideband is correct because when it reads 17+ it idles rough and will try to pop back through the intake if I try to rev it. after throwing itself back to open loop a few times the AFR will settle a bit in closed at about 16.5 at an idle. The only way this car will run good is open loop. I tried to log the idle with datamaster and it keeps losing connection, monitor for a few seconds and stop and then start working again. Thought maybe something was wrong with the cable but must not be because I can tune the car with CATS no problem. I can also monitor fine with my autoxray so the pcm must be communicating fine also.