'96 LT1

My Long Term fuel trim is running 139 on bank 1 and 145 on bank 2. The O2's are new Delphi. New Delphi MAF sensor. New FMS 30# injectors. No vacuum leaks that I can find or exhaust leaks that I can hear. The car is running really good and the only thing I can complain about is the idle quality. The MAF sensor helped that a lot and with throttle response as well. Short term fuel trim is spot on at 128 on both sides. Ideas?

226/230 .565.565 111 lsa
stock heads
LT headers

Quote:

Adjust your fuel tables..

The 111 lsa is not helping, you may also want to consider changing your 02 thresholds. Cam has what, about 70 degrees overlap?


-- Joe

LE cams all have tight lsa's. what is it doing that you doint like about it?

Quote:

More overlap, confuses the narrowband 02.

-- Joe

Thanks guys,
I'll just keep working with the tuner on it.

Sounds like it does need a hair more fuel in that area, but don't go crazy with it. I am running a '89, so totally different, but a 110 LSA cam. I ended up going to open loop tuning to get it to run right. Mine would think it was lean at very very light throttle, due to fresh air going straight out the exhaust. The blms would keep going up and up very fast, and it would read very lean on the wideband too....until I gave it a little more throttle, then the blms would drop like a rock, and it would be very rich on the wideband. Open loop was my only fix.

Sounds like you are fairly close and might get it worked out on closed loop, but if you find a spot at idle or very light throttle cruise that it just refuses to come down in blms no matter how much fuel you add, then gets very rich when you give it a touch more throttle and then the blms tank, you might be having the same issue.

If you can narrow it down to just idle or just one fuel trim cell, try letting it idle for a long time or driving in that fuel trim cell for a long time, then shut it off and check the spark plugs. If it is fresh air going out the exhaust screwing up the 02 sensor, the plugs should still read good. Add or subtract fuel then do it again till you get the plugs looking like they should. If it is doing it in more than just one fuel trim cell then this method won't work and you will likely need to run open loop.

One other thing that never really gets allot of looks is the IAC. It is a cause for vacuum leaks etc. It doesnt give a code, and the only thing you see on datalogging is what the ECM is telling the IAC to do.
Mine gave me less than desireable idle, for example, so I was unable to use AC at idle etc while in gear. I replaced everything, but it turned out my IAC was bad. I recommend you at least take it out and clean it, unless it is new as I know you went through allot on the older threads.

Quote:

Thanks Steve, the IAC is new and the passage way is clean.

Not sure if this could cause my fuel trim issue or not but I think my fuel pump check valve is bad. I ordered a Racetronix replacement pump and it should be here next week I hope. If it doesn't help I'll just keep working with my tuner on it to see if he can tweak it a little more.