Ωhm

What seems odd to me is the loss of 1.3 lbs/hr should cause LTFT (go above 128) to increase INJ PW time (ms). But so many other factors come into play here. Throttle bodies, exhaust systems etc, etc. But O2S switching (RICH LEAN) will always try to find 14.7 to 1 (stoichiometric fuel ratio).

Good read.

Its just you and JMO413 that's tracking LTFT. These numbers are real world stuff. Random, I don't know, but yes it could be ECU characteristic.

Too me, LTFT of 91 means O2S sees RICH and LTFT 91 is taking fuel away (decreasing INJ PW time (ms)).

Must have some kinda memory, possibly KAM. Yours is a 90 ECU?

Good (only in sense of the) recording showing movement on LTFT. Does the ECU retain that value after a KEY OFF or say the next day?

Regardless of the cause, ECU uses 0-255, starting at 128 (STFT or LTFT) to determine if it needs OPEN loop or if engine can stay at CLOSED loop (with O2S feedback).

Its range of authority. O2S is boss. MAP, TPS, ECT & MAT values are used at every given time to determine INJ pulsewidth (ms). This determination goes to a lookup table and picks the correct INJ PW (ms) value for each engine condition. Rate of change also plays into this lookup (MAP & TPS). This type of fuel strategy is called Speed Density. Only the O2S through STFT & LTFT can add or subtract time (ms) from the fixed lookup values.

True, but JD's question was "What pressure were they tested at to determine there flow rate (lbs)".

The terms RICH and LEAN here are what the O2S sees.

My thinking/guess is ALFACL is STFT only.

Yes, 128 is the starting point for both STFT and LTFT.

It's confusing, yes. Number below 128 take fuel away (decreasing INJ PW time, O2S sees RICH engine). Number above 128 add fuel (increasing INJ PW time, O2S sees LEAN engine). In your case O2S sees RICH engine.

I too, would like to know more about this subject (STFT LTFT). I wonder if all ECU's are created equal. Does a 90 ECU offer more than say a 87 ECU, when it comes to Fuel Trim. 87MJTIM shows LTFT at 154 while other ECU's LTFT don't move and vehicle goes CLSD loop once STFT pegs one way or the other. Anyone else show LTFT movement? What year ECU? 87MFTIM does your LTFT value stay the same between KEY ON and KEY OFF cycles? If so, does that indicate Keep Alive Memory (KAM). Doesn't 154 mean engine is running lean and LTFT is increasing INJ PW time? Just the opposite here, doesn't below 128 mean engine is running rich and STFT is decreasing INJ PW time?

Did your idle smooth out?

STFT is O2S switching based. More lean or more rich move the STFT numbers which will adds or remove fuel through INJ PW times. When STFT reaches either one of its two limits, LTFT should move in the same direction, adding or subtracting a few number, resetting STFT (128) and starting the whole process over again.

I'm not saying that, I'm wondering if it will. LTFT should trigger when STFT reaches one of its two limits (0 or 255). LTFT will then move lower or higher, allowing STFT (128) to start all over again. Thats the intent of STFT and LTFT. Now what I don't know is if RENIX will do this.

Could it possibly take 3-4 days to trip LTFT? Keep an eye on it.

Maybe number 3 is your lucky number. Keep us posted.

You've mentioned Indexing the distributor before, not sure if that could cause a idle problem like your recordings show. Have you ever run a compression test on each cylinders?

That last recording look normal and seems well within its range of authority. MT2500 only reads and displays live data, so O2S circuits should be good. Hope this new O2S solves the problem.

You're correct, I was using (O2) V as INJ PW. Can't see INJ PW on screen.

Your recording show engine is running RICH. It's in CLSD loop, STFT is taking fuel away (noted by low INJ PW).

Not trying to be a smartazz here, but have you check the battery in your DMM? Did you note the STFT and LTFT numbers when installing new O2?