Fuel Trims irregular

[kmplace22]

I have been fighting this issue for a few weeks now. the fuel trims will be off as much as +- 15% at idle and tapper to near 0 as rpm goes up. I checked for vacuum leaks and dont find any and same issue. A few more minutes into the log fuel trims are back to normal. I have been using this MAF curve for a few months now and have had zero issues until recently and verified that by going back and checking old logs. Car is 12 gt with JLT2 CAI, no cats with pypes axle back. Im looking for someone who may have experienced similar issues or have any ideas at what to look at. Ill attach log that shows trims off at beginning of log and a few throttle blips and trims come back to normal. I have searched quite a bit but not have not found anything that is the obvious answer.

[aaronson]

Try dialing in your MAF v. Period a bit more in the idle period region. A little adjustment aka 1-5% can make a huge difference in fuel trims

[CCS86]

Try dialing in your MAF v. Period a bit more in the idle period region. A little adjustment aka 1-5% can make a huge difference in fuel trims

A little adjustment of the MAF curve (1% - 5%), can only change your fuel trims 1% - 5%.

[kmplace22]

to be clear this Maf curve has been 2-3% at the times it behave correctly, at the end of the log at idle you can see the trims come right back to normal. it has to be something that is affecting it from the outside, purge or a intermittent issue of a sensor.

[CCS86]

Looks like a typical, piece-of-trash, MAF curve. Anyone building MAF housings and either not providing a MAF transfer function, or providing what JLT does, should be left to go out of business.

If it were me, I would go to some type of OEM Ford MAF housing and transfer function.

Here's what yours looks like:

JLT trash curve.jpg

[CCS86]

I agree that you have another issue besides the MAF table, though.

In basically the same MAF table cell, you have STFTs ranging from -14% to +6%. However, most of that is because your LTFTs were adding ~11% fuel at the beginning. So, at some point it's learning a need to add fuel, and other times it is backing that out.

I would disable long term trims and focus on tuning for better STFTs. If you are running EVAP, I would try disabling it. I found that it made large fuel trim swings on my car, long enough to learn a bogus correction.

[08cobra]

i am a beginner with the HP tuners but i had the same issue, my cooling fan was cycling on and off and it would change my trims 25%. i relocated the air filter

[decipha]

if the error is during startup enrichment that means your enrichment fuel table needs to be dialed in.

[kmplace22]

A little update on this issue. After reading 08 cobras response to when the fans came on i payed more attention to when the trims would go irregular! And thats exactly when it happens. every time the cooling fans came on the trims go +15-20%..... i built some shrouding with cardboard to see if turbulence was the issue. That helped a few % but did not solve the issue...i do notice when the fans come on i get a good rpm drop.... so i will look into more bad connections/grounds or possibly some alternator issues although PCM voltage rides around 14v during this.stft.PNG you can see in this snippet that distinctly when stft go to "normal" and then fans come on and the go +