F150Torqued

We definitely agree on that point. But we need to work on another one. Though maybe with conceptual semantics only. The devil can be in the details for the OP here, so let us leave no stone unturned.

'BASE' injector pulse width is a factory programmed parameter stored in a matrix somewhere (we can liken exactly to the Fuel Trim Tables), based on _at least_ two variables. RPM and Load. Engine Load _IS_ calculated based on MAF reading, Baro(), IAT - plus perhaps other factors IDK. But in this way, MAF has an effect on WHICH base injector pulse width is selected as the BASE injector pulse time for current RPM/LOAD with NO fuel trim adjustment added to it AT ALL.

Fuel "TRIM" is strictly a function of repetitive reads from O2 sensors reading of combustion by-products. If Oxygen is present in exhaust (O2 volts < .45 v), STFT is incremented upward a notch. Next read = same test, about 6 times per second. If NO Oxygen is present in exhaust ( O2 volts > .45 v), STFT is incremented downward. The current value is added to the Base of ONE. And somewhere along here - a portion of STFT is 'sifted' into LTFT for longer term usage so STFT maintains ^ and v adjustment.

How can idle STFT be negative (other than too much FUEL delivery)? If the EGR is leaking, Exhaust gases can be getting into the intake and a given amount of air is diluted with inert exhaust gasses (making O2 readings ^ .45 v, thus decreasing STFT. I am unfamiliar with the EGR unit, but if the gasket is bad, or if atmospheric AIR leaks into recirculation path - I believe would replicate the OP's symptoms

Do like us stupid red necks. BEAT ON THE EGR WITH THE BUTT OF A SCREWDRIVER AND RUN THE FUEL TRIM TESTS AGAIN.

BareBonesXL

Referring to Steve83's comment about the IACV -

Pretty sure that's a different valve. The IACV lets air past the throttle blade, but it's metered air so wouldn't change the mixture. The IACV is controlled by the PCM, for fast idle when cold among other controls.

I'm familiar with idle air mixture screws. I have one on my old Datsun.

I agree about idle speed controlled by timing, in addition to idle speed controlled by IACV. I think it's one of the things that makes the propane test for vacuum leaks difficult to do without seeing trim numbers. The PCM can react too fast to hear the idle speed change.

BareBonesXL

The "trim" that you see on your reader is the difference from that expected pulse width. It basically tells you far off the injector open duration is from that expected value in the table.

These things are definitely difficult to describe in words, on the internet, on a Saturday night.

F150Torqued

^^^^^^ ^^^^^ now I believe we're on the same page. Even via words, on the internet, and on Saturday night. Cheers

goinwheelin

Hey guys, sorry for the delay getting back to you, i'm just crazy busy.
So first things first. I guess I misinformed you guys about my live data pics, so just to clarify them the first one at 729 rpm is idle (obviously) but 1562 rpm is "Under Load" and the final pic is just high rpm (no load). Sorry for the confusion.

But I was able to perform a couple tests tonight. So I disconected my egr vacuum and plugged it and watched fuel trims.... No change at idle or under load but did get some rattling or pinging while putting my foot into it a bit.

Maf sensor at idle 5.30 - 5.42 g/s. Blocked intake slightly with my hand and g/s drops. Cant really say what the number was cause the engine wanted to stall but I did see 4.17 g/s a couple times.

Vacuum pump connected to egr valve and pumped it up to 12 in-hg (engine not running). Vacuum held. Same test performed while engine at idle and at just min. vacuum engine wants to stall, which brings me to my next question period.

When I disconected the egr vacuum I put my finger over the hole and dont really seem to have any vacuum but it feels more like a vibration or pulsation at idle and about 2000 rpm. Also at shut down my electronic vacuum regulator buzzes.

Are these things normal?

As for the propane test, I have done that test as well as carb cleaner with no results but not with live data which I definatly will try just no time tonight. Its really hard to do anything on my truck right now cause as I said crazy busy. As the saying goes, ya gotta make hay while the sun shines.

Thanks so much again guys.

F150Torqued

Hey @goinwheelin

I jus browsed back by to see what was going on with your fuel trims and skim read your posts again. I noticed something I had missed the first time. You said:

Without live data, you can't successfully do a carb cleaner or propane vacuum leak test. The PCM is much too fast at compensating for the ingestion of the propane or carb cleaner. It will adjust for the change in fuel / air mixture and idle will not be noticeably different. That is the whole idea of monitoring live data. YOU SEE FUEL TRIMS - the exact parameter the PCM adjusts to keep idle from changing.

Since you can read fuel trims live, I hope you have tried this test.

F150Torqued

Hey @goinwheelin

You still chasin' your tail over them Fuel Trim Readings?

Jest' wonderin'

goinwheelin

Hey F150Torqued, sorry for the delay but its fishing season here and was busy reelin them in.
Well i do have them numbers closer to spec than they were, had to change the maf and an o2 now ive got the numbers to normal under load but at idle the long term is still slightly negative by that i mean -12 to -15 but no more mil light and now im getting a bit of a knock at cold startup but only for about 30 seconds. Gotta look into that asap.
Thanks again for all your help and to everyone else as well

F150Torqued

Thanks for the update and glad to hear your lean code MIL is gone.

In the FWIW department - (?????). Something is still slightly amiss. You are not 'far' from a RICH Code. WHY? You didn't mention STFT, but LTFT & STFT are added together for both adjusting injector pulse width AND comparing against the DTC trigger points. Negative fuel trims suggest the average O2 sensor readings improve when the injector pulse width is 'shortened'. LTFT is best viewed as a historical indicator for STFT. IF STFT is near zero - and LTFT is skewed - it simply means LTFT is able to handle the condition and full range of control (above / below zero) is returned to STFT. Or it could suggest the 'problem' causing the condition is temporary and has gone away - for now.

Negative fuel trims are less common than positive, and have completely different diagnostic angles. (Excessive fuel pressure, leaky / weeping fuel injectors, hydrocarbon rich air getting into the intake [from leaky EVAP purge valve], or a correction process from a temporary lean condition.) If STFT 'bobbles' negative enough times and returns to ZERO, it will make LTFT negative.

Fuel trims being off at idle is more common. Lower air flow amplifies the effect of fuel / air mixture. STFT zero and LTFT negative 'could' be result of a leaky or weeping injector. Over rich at startup - which is burnt off shortly and STFT returns to zero leaving low rpm LTFT negative.

Just some thoughts, Might be something still going on, though not real serious (YET).