Trims not holding between starts

[sohcstealth]

As the title says, I've noticed that my ECU is not holding the low, mid and high trims between engine starts.

The car is a '91 TT, both O2's cycle perfectly at idle and it runs great otherwise.

Can anyone shed any light on the subject?

Thanx in advance!

[Greg E]

The ECU is losing power when the ignition is shut off. This is causing it to reset.

Much like when the battery is disconnected and you have to reset the clock on the radio.

[RealMcCoy]

So they all go to 100 after you turn the key off? Check the keep alive power (should come from the IOD circuit fuse 19)

[sohcstealth]

Yes, they all reset to 100 as if the battery was disconnected. I pulled the IOD yesterday to see if it had any effect on the problem. Doing this made no difference, aside from the HVAC resetting ( I.e. A/C on on restart)

I will have to look at my manual to verify that Ecu power is routed through that circuit.

[stealthee]

Pulling the IOD will cause exactly what you have going on. There are a few different fuses that you need to check to see if they are blown.

[sergechronos]

Pulling IOD and it resetting the HVAC which it didn't do before (even though battery power for ecu is getting reset) may help pinpoint the issue. Perhaps a short or break in the wiring for the ecu or at least narrowing it down to wiring that doesn't share the same iod element as the HVAC system.

[sohcstealth]

Thanx for the help guys!

I ended up removing and inspecting the ecu and wiring. ECU has been replaced at some point with a newer OEM unit, however, I did find one pin to have some light corrosion and both "Ignition coil a" and "ignition coil c" wires to have a small break.

I taped up the breaks and also tested for power at the Ecu with the key in the off position, across pins 60 (Backup power) and 26 (ground), as per the service manual.

Turns out there was power at the ecu and fixing the breaks seemed to remedy the problem. The car is now holding the trims between starts as it should.