Nistune Forums

ah that must be the Diagnostic idle RPM control. does that pot do anything besides setting the 2 modes on a stock ecu? it must have done something?

It is idle control (about 100rpm or so) in one position, and then diagnostic mode on the other position. It also in idle control mode sets the two LEDs to flash or stay solid when rich/lean during O2 learning (refer service manual). The diag pot number adjusts between 0-255 and replaces the input on the ECU

any luck with the updated image?

Yes its now in the FP3 ROM pack, 19P1H is what you need for the 1986 ECU

From what we found in the previous posts was only the AC switch was affected by using the 1988 ECU updates and all other functions seem to be the same

Including the long term o2 control?

LTFT would not come from the ECU hardware specific inputs, so shouldn't be affected. However I did not look into that one. I don't see it mentioned on this thread before? Was it on another thread?

yes it was sorry. Im not sure that the LTFT is correctly displaying. it seems to change rather rapidly.

i attached a log and the rom im using. the rom might have been tweaked a bit for idle settings. but this is the most current i have.

Attached screenshot shows STFT/LTFT and adjusting O2 sensor

You will see that STFT is quite rapid (zoomed in) but LTFT only moving a small amount over time. This is with 19P12 in a 1986 ECU

Here is 26P0F in 1986 ECU. Functions the same. Small adjustments in LTFT

This is your log which goes for 15 minutes, so I'll just pick a spot (14:50)

Here we can see where the MAF and RPM and smooth (not much change to load cell positioning) that the STFT is following the O2 sensor up/down movement

We also see only small fluctuations to the LTFT Now.... if you look elsewhere in the log. You will see more changes to the LTFT as you move through various cells. From what I've seen, the ECU will store the LTFT in battery backed up memory and then reference those long term saved references when in closed loop, and then does LTFT+STFT to adjust the injection time

What is why you are noticing the fluctation. In a steady state (around similar cells on cruise) the LTFT does not change much, except how how adjusts to STFT trimmings

You will notice your trimmings on the input trace window above. I did a fast playback to capture the trims over the map. This would be similar to what the ECU has in RAM and then readjusts those trims

There appears to be a global LTFT adjustment too since if I hold lean enough on a point in the map then both STFT and LTFT will reach maximum (25% extra adjust) trim and then apply that to the rest of the map. However outside the closed loop area it is not used