I have a lean to rich issue
Hi my truck is a 1983 full size Jimmy with a newly built (by me) 350 sbc and FiTech 600 power adder.
Engine was dyno at 300hp, naturally aspirated.
I need your guys help with what parameters I should change to solve two problems:
1. Get rid of the rich spot I get (mostly comes after a momentary lean spot) while accelerating.
2. Get rid of the lean spot at idle (while deaccelerating).
I did try to tune a little, increased the dTPS acc gain from 118 to 150 and the fast accel to -15. IAC usually at 5 while idling.
I'm attaching a few screen captures of a log from a drive I did yesterday.
Please ask questions, will try to answer them all.
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Bring your IAC to up over 10 at idle.
What you want to adjust is the lean tip in. When you tip in the throttle it goes lean which means your Accel enrichment is not enough. Adjust Accel first for normal throttle tip in for everyday style driving. When you get that leveled out, then adjust your Fast Accel for fast throttle changes.
When you see the lean to rich, that is the unit trying to quickly bring the AFR back to Target. It will usually over compensate causing the mixture to go slightly rich for a moment then level off. When you get your Accel right the unit won't try so hard.
Thanks for the reply.
Everywhere I looked it says IAC up to 10 at idle.
When I'm on gear at a stop the IAC falls a bit and ends up at around 3-5.
How high do you suggest to raise it and why?
Fitech Instructions say 5-10 if my memory serves me correct. Many of us have started running them slightly higher with good results. The idea being that the steps never hit zero and has room to adjust to all conditions.
Simply turn your idle screw counter clockwise to effectively get the IAC steps to raise. It won't take much....
Austin, isn't there some relearning for the ecu when the idle screwed is adjusted? I have been fighting the same issues Rob has; lean tip in and way lean to pig rich on wot throttle stabs.
I added the IAC information and I guess you are right, IAC does reach 0 when pulling to a stop.
I'll make the change, I've done this type of tune before.
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Quote from texcuda on March 6, 2019, 2:34 pmAustin, isn't there some relearning for the ecu when the idle screwed is adjusted? I have been fighting the same issues Rob has; lean tip in and way lean to pig rich on wot throttle stabs.
As I told Rob earlier. Adjust your Accel and Fast Accel for the lean condition. The rich side is the unit trying to quickly compensate.
Also make sure you don't have a fuel pressure drop during your lean condition....