edmcguirk

Well, I never would have guessed this. It seems to be a problem with the supply voltage/ ground.

I have gone around and removed various parts that are not required to be street legal and are not needed on a race car (like both idle control valves) and I have replaced the gasket that I split when I pulled the UIM.

It turns out that my high idle was not a vacuum leak but somehow the High Idle Adjustment was not set right. I don't see any way to adjust that without taking the manifold apart again so I put a rubber cap as a spacer on the thermowax piston and it got the idle down for now.

After each part was removed the car seemed to run slightly better but the problem would never completely go away. I finally got the car to go into closed loop during a test ride one Sunday morning so I thought it was fixed and I re-installed the ACV so I could go to get inspected on the Monday evening late hours. Unfortunately, after re-installing the ACV, the car would not go into closed loop on my test ride Sunday night.

After driving myself nuts looking for another problem, making small changes, and going for test rides, I found it very strange that I could get closed loop during the day but not at night.

Some people suggested temperature, some suggested moisture, etc, but it turned out that every time I turned on the headlights or anything that would draw a large amount of current, the car would go lean and fall out of closed loop mode.

During all the part swaps I did not bolt the ECU back to the floor and I hope that's the problem. Otherwise i will have to go examining all the grounds in the car for a bad connection. (anyplace else I should look?)

(the voltmeter shows good voltage (comfortably above 12 volts) and it does not dip much when I turn on the headlights. So I don't think the problem is in the alternator)

It doesn't look like I had one problem but instead a lot of little problems that added together enough to prevent the ECU from going into closed loop mode.

ed

edmcguirk

Bad luck for me. The replacement ECU was loose but when it didn't make any difference, I plugged the original ECU back in.

The original ECU was bolted down the whole time.

My only guess will be to run a ground wire from the battery to the engine to the ECU this weekend and hope that helps.

I'll also measure the voltage with a meter to see if it fades any.

Any other suggestions?

ed