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High LTFT at idle

Posted: Mon Oct 23, 2017 1:10 pm
by Rich A
My Long Term Fuel Trim (LTFT) is high + at idle.
Where can I go to adjust the AFR to richen up the
mixture without affecting the part throttle upper
RPM range AFR mixture? (Commando software)

Re: High LTFT at idle

Posted: Tue Oct 24, 2017 5:22 pm
by Sniper Chris
What's year, make and model?
What is the LTFT values?
What is the MAF voltage at idle while LTFT are high?

Re: High LTFT at idle

Posted: Tue Oct 24, 2017 10:17 pm
by Rich A
‘96 Ford Explorer
STFT -4.7 LTFT 10.9%
STFT -7.0 LTFT 6.2%
Air flow rate MAF 8.23 g/s, 1.02 lb/min
80mm LMAF
6 psi Centrifugal Supercharged

Re: High LTFT at idle

Posted: Wed Oct 25, 2017 10:16 am
by Sniper Chris
Obviously you want to be as close to 0% as possible but those numbers are still within specifications (10-15%). I'm not seeing any issues there. Are the trim numbers jumping around (fluctuating) or are they just staying solid?

Re: High LTFT at idle

Posted: Wed Oct 25, 2017 10:46 am
by Rich A
The fuel trim numbers are fluctuating.
They just seem high,
would like to get them lower if possible.

Re: High LTFT at idle

Posted: Thu Oct 26, 2017 11:29 am
by Sniper Chris
Assuming everything is sound with the engine, sensors and no vacuum leaks, you can try this. Because your stft are negative and your ltft are positive we really don't know which way to make the adjustment. I would start be adding 5% fuel. You would make this change in the MAF transfer function.

This is why I asked what the MAF voltage was at idle. I'm guessing that it may be around 1v. So, add 5% fuel from 1v to 0v. However, you need to make sure after adding 5% that the value at 1v is not a higher number than the next volt figure (maybe 1.1v?).

If adding the fuel doesn't seem to be helping then go the opposite direction. Pull 5% fuel