So what is the trick with these 04+ grand prix's getting the LTFT's to lock at zero? I'm using the HP tuner and for the life of me I cant get the trims to lock at zero. They usually lock at -3.1 or -1.5 I followed the directions on the HPtuners forum forcing the car into open loop (in a nut shell you set the commanded afr to 14.7 and zero all the adder tables and zero the pe table) and all of the maf /afr % error tables were like -1 to -2 % The maf table I'm using is a stock 5.3 liter truck table for the larger 85mm maf. The trims normally hang in the -2 to 1 range so why dont my trims lock at zero.


I'm in the process of tuning the upper end of the maf curve so the actual afr and commanded match. Everything gets thrown out of wack if the trims dont lock at zero.

Please help, I'v been messing with this thing all day and not getting anywhere with the locking issue.

Sometimes it just takes a while. When I first started tuning it took me two days to get my fuel trims to lock in at zero.

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I never had any problems zeroing out my LTFTs and I didn't zero out any modifiers or the AFR. Just scan in 3rd gear for more precision. Drive at different speeds for awhile without going into PE mode. Keep out of boost. Use Ed's Tuning Thingy to make the changes to you MAF table. After importing the new table in, make sure you reset your trims.
04's are not like pregens that you can tune every 20 minutes. It sometimes takes a few days for the trims to settle in.

I tried using the "forced open loop method" just to see how far the overall maf curve was. what I'm really having trouble with is the open loop method showed that the commanded vs actual afr's were only off by +/- 1 % and as I said earlier was my trims before messing with them are in the -3 to +1 range, so how close do I have to get the ltft to get them to lock at zero?

I can also see how the trims swing alot before they settle in. is it recommed to get the trims settled in before going into pe?

I was also doing some scanning from a cold start and noticed that my commanded afr was like +15.6 and then dropped to 14.7 after it was warmed up. I thought the afr should start rich and then lean as it warmes up. any thought there?

And for the last question of the night. Am I correct in tuning my upper end maf 7620 and up or the PE portion so that the commanded Vs actual afr match? It seems strange to zero out all of the adder tables when I could easily change the base afr and adjust the rpm vs time adder table to reach my target afr.

Thanks for the help guys, I'm definately behing the eight ball with tuning.

You should probably tune the entire table at once. The table should form a nice smooth curve if you bring it in Excel and make a graph. Any hickups in that curve will really screw with your PCM. If you are only tuning one part of the table, there's bound to be a jump in between the the part you change and the part you didn't change.

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3.5" MPS, 1.84 Rockers, 3" DP, Frt PEM, 39lb Injs., PowrTuner, Wizair
14.07@ 98.85mph 2.180 60'