Here's one to ponder for those of you with tons of ECU knowledge. First, the background: This is a 90 245. Vehicle was purchased with a blown engine and autobox with the intention of building a new engine and converting it to manual trans. Engine had been partially disassembled. Along with lots of other strange damage, one of the things I found wrong with the car was that the threads for the cold start injector were stripped. Injector was loose. In rebuilding, for whatever reason I could not seem to dig up the right manifold, so I went with an earlier, LH2.2 manifold instead. To compensate, I swapped out the 933 ECU it had with a 951. This is based on my understanding that these later ECUs provide cold start via the regular injectors. I also chose the 951 because I need EGR for CA.

Fast forward to starting day. In typical LH fashion the engine fired right up and after some adjustments ran just fine. Exhaust was an open headpipe with the cat-mounted O2 sensor just strapped to the trans temporarily. It did not surprise me when the check engine light came on first time I took the car out on the street. Didn't bother to check the codes.

Installed the exhaust a few days ago and a brand new sensor. Cleared the codes, but the CEL came back with a 123 code for the ECT signal. Found Lucid's old post on the feeds--all good. Engine has a brand new ECT sensor from Bosch and since the readings were good, I swapped the 933 ECU back in on a hunch.

Cleared the code and it has not returned.

Certainly the ECT sensor and the cold start settings are intertwined. But how could the ECU change affect this?

DS