Quick question(s) on STFT

[WildHorse]

Couple questions concerning a custom tune. LTFT can move +/- 5-6% (more?) as it cumulates and learns, LTFT attempts to keep STFT with in 1-2%. This is totally normal. LTFT is slow so if it is able to keep STFT around 1-2% the MAF curve is accurate. If this is the case, why would my STFT around 12-14% ? Second question : Ideal WOT AFR should be around the mid 12's. Why would it be mid to high 11's ? I'm thinking this is related to my first comment. No pending or CEL. Thanks.

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[GregO]

Ideal WOT AFR should be around the mid 12's. Why would it be mid to high 11's ?

Take this with a grain of salt but best WOT full load power is achieved around 11.5ish A/F depending on type of gasoline.
If it’s not tripping DTC I’d take WOT 11.5 A/F all day long.
I’m old school and I’m use to seeing BSFC as a metric for proper fueling under load.

 

[WildHorse]

Take this with a grain of salt but best WOT fully load power is achieved around 11.5 A/F. If it’s not tripping DTC I’d take WOT 11.5 A/F all day long.
I’m old school and I’m use to seeing BSFC as a metric of proper fueling under load.

Even if you see a bunch of unburnt fuel out the tailpipe. Throughout the WOT ?

 

[GregO]

Even if you see a bunch of unburnt fuel out the tailpipe. Throughout the WOT ?

What fuel are you running ?
Any additives ?

 

[WildHorse]

What fuel are you running ?
Any additives ?

91 E10, zero additives, and as a side bonus, zero knock with all that fuel haha. Still don't understand why the STFT is 12%-14%.

 

[FreePenguin]

91 E10, zero additives, and as a side bonus, zero knock with all that fuel haha. Still don't understand why the STFT is 12%-14%.

not pertinent because I am ecoboost and you are big Dady gas eater.

but when I had my downpipe, I had an exhaust leak, I was getting like 6-12 STFT and like 10-15% LTFT, and my bumper, the rear valence or whatever the center painted piece, was COATED in black. in 25k miles with oem downpipe, no exhaust leak, it was never like that.

anyway long story short, I fixed the leaks, and the shit went back to normal. depending on the day, I am usually 0-4% trims combined, but if there's a massive fuel swing, ie. going from 80* day to 20* day it'll do large corrections of adding or subtracting to correct, but when temps reugalize I sit at 0-4% trims

 

[GregO]

Still don't understand why the STFT is 12%-14%.

That’s out of my wheelhouse.

Is there any merit to testing the ethanol level in your fuel ?

 

[WildHorse]

Is there any merit to testing the ethanol level in your fuel ?

Guess I could. I need to purchase one of those testers though.

 

[Nuked]

0.83-0.85 lambda is normally where tuned Coyotes run NA at WOT.

Short term trims can swing under sudden throttle changes, so if you see that its pretty normal. To scale the MAF one way is to disable the LTFT, start at a low rpm and slowly increase the rpms up to as high as possible while holding the same gear and similar throttle position. There are some other things to disable when doing it but I cannot remember what off top of my head. The spots where it adds or pulls fuel via STFT you would make the adjustments to the MAF table.

 

[Dr. Norts]

If the LTFT start trending up positive as well due to the high STFT you're getting unmetered air into your engine somehow and the STFT are adjusting to add more fuel to compensate for this.

If your just seeing it on throttle tip in this is normal behaviour but if it's staying like that causing LTFT to trend + higher I'd look for an air leak letting unmetered air past the MAF first.

You can reset the ecu / fuel trims and you'll see the LTFT trend up alot faster and be able to see if this is the case vs waiting days or longer for it to trend upwards.

 

[WildHorse]

All right. So I compared it to stock. It's definitely MAF wash. Wigging out the MAF while cruising. ONLY thing I did was open up the grill. So apparently the MAF doesn't like that.

 

[GregO]

ONLY thing I did was open up the grill.

Didn’t you work on sealing up the filter area in an attempt to keep IAT lower ?

 

[WildHorse]

Didn’t you work on sealing up the filter area in an attempt to keep IAT lower ?

Yeah bud.. last minute I decided to open the grill, shortly after is when I noticed the problems. Turns out, I, and others, are NOT smarter than FORD engineers. Haha.

 

[GregO]

last minute I decided to open the grill, shortly after is when I noticed the problems.

I remember early on that the guys at PMAS discourage sealing up the filter area.
Something about low turbulence over everything sealed up to mitigate heat.
That was several years back, actually think it was on their FB page.
I’d still like to know what IAT's read at the intake port right before the fuel injector vs. MAF IAT reading.
Ford must know something or they’d be pulling timing long before 150 deg IAT. Don’t you think ?

 

[WildHorse]

I remember early on that the guys at PMAS discourage sealing up the filter area.
Something about low turbulence over everything sealed up to mitigate heat.
That was several years back, actually think it was on their FB page.
I’d still like to know what IAT's read at the intake port right before the fuel injector vs. MAF IAT reading.
Ford must know something or they’d be pulling timing long before 150 deg IAT. Don’t you think ?

Ok, I'll put the gen 2 PMAS heat shield back on, without sealing it to anything. Just to see if the wash is really the culprit here. And yes, I'm beginning to think high IAT isn't the end of the world.

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