Can't figure this one out could use some advice

[Rex2342]

I'm trying to help my buddy out and can't figure out why his low fuel trims won't rise from 81.2? He's running a SB M60, 255, Aeromotive AFPR(set @38psi), 780cc injectors, SAFC, 3" GM MAF with MAFT, and a MMCD logger. No matter what I do his low trim will not stay put. I've leaned everything out as far as I could and the highest it would climb to was 84.* and then drop back down to 81.2. His FTO2 is even acting wierd. It will bounce between 95-105 for a minute and then falls to 80, 70, and even 60. He just replaced his O2 sensor too. His car also takes forever to read FTO2 on the logger and on his A/F guage. My logger reads withing a minute or so of starting and my A/F guage comes on right away but his is closer to 8-10 minutes before a signal is read on either. ANybody have any ideas on where to begin?

 

[Maglin]

Well first off the injectors are to big. You are probably not going to get the low trim to rise with tuning with a SAFC/MAFT. They both do the same thing so anything over 660's is just to big. And with that big a turbo it's going to be either running very very rich on top or way to much timing cause of all the fuel you are going to be tring to pull.

Best thing to do is either get a standalone, chipped EPROM ECU, or DSMLink. I think it would run better with the 450's back in and raise the fuel pressure to 45 PSI and run 17-18 PSI. You can have a great idle and lean it out on top and not have crazy timing advance. They would be flowing like 510cc injectors at the fuel pressure. I would tune it that way and hold the 780's until you have a better way to tune.

Or you can kept them lean it way out on top. Deal with a very rich low end. Run 15 PSI cause of crazy timing advance on top and also get very crappy fuel milage. I'm running 1000's and still get like 24 mgp in the city. Anything bigger is going to have a hard time with having a stioch idle with the stock ecu and dsmlink/chip.

 

[chris4g63t]

Try lowering the fp a couple psi. My fuel tims are in the 80's and I still get 26mpgs so I wouldnt worry about it too much if I were tou.

 

[Rex2342]

Well he swapped out a set of 660's because they were running at 120%+ duty cycle but that was before I installed the AFPR for him. He had a B&M unit before that and it was causing all sorts of problems and a base fuel pressure of 52psi. Maybe I'll swap back to the 660's with the new AFPR and see what that does. He says it's running good but it's very rich at idle and low speed.