Fuel Trims
 

Calling all Gurus;
I’ve recently installed an LT4 stroker in my 94 F-body and I’m having some trouble with long term fuel trims. I have checked the exhaust system for leaks as well as the intake system and they seem fine. The o2s were replaced with engine and the pcm was reprogrammed by PCM For Less. When I first ran the motor it had open headers which caused the o2s to see a lean condition and dump fuel. Once the exhaust was connected, the left bank showed LT 115 and the right LT 160.

I adjusted the throttle stop screw to bring the IAC to 45 (from 87) and set the TPS to .67 volts, which now causes both long term fuel trims to max out at 160 as read with my OTC scanner. When I removed the BBK 58mm throttle body to look in the intake, everything had a slick coating with traces of carbon. It appears that there is some exhaust drawback and gasoline saturation going on in there. The cam is not that radical, .230 in / .236 ex duration; .520 in/ .530 ex @1.5 ratio, and I think my vacuum is at about 15hg so I wouldn’t think reverberation would be severe. Fuel pressure is set to 50psi using 32lb Accell injectors.

Here’s the scanner readings…

Air sol, off
Asr cntr, no
Baro press , 30 iHg
Baro volts, 4.96
Bat volts, 13.2
Blm cell, 16
Blm enable, yes
Cc d/c (%), 0%
Cool temp, 177 f
Egr d/c (%), 0%
Engine rpm, 909
IAC, 45
Injector flt, no
IPW bank1, 4.13ms
IPW bank2, 4.55ms
Knk retard, 1%
Knk signal, no
Ks sensor , ok
Learn IAC, 39
Left Ho2, 0.34mv
Low res sig, 17.1ms
Loop stat, clsd
LT fuel1, 160
LT fuel2, 160
MAF, 10.9 g/s
MAP, 15 iHg
MAP volts, 2.23v
MAT, 113 f
RT Ho2, 0.40v
Spark adv, 25
ST fuel 1, 141
ST fuel 2, 151
THR angle, 0 %
TPS, 0.69v

The next thing I will do is check the valve adjustment, but I used a very reputable engine builder so I doubt that’s the problem. Maybe somebody has the wherewithall to see something from the above data. Please note the o2 readings because they are so widely different, yet both banks are dumping fuel. I've been at this for weeks now and I'm running out of ideas. I have been impressed with the collective knowledge of this group. Thanks for being there for eachother. :bow: :bow: