Dave Parker

There is another thread started by me that goes through problems I had with my 911SC CIS system. Since the solution was one that no one thought of, I thought I would post it as a new thread in case someone else was having similar problems. If you want the whole story look for my other thread.

Here is the final solution:
FINAL SOLUTION ... It wasn't any of the previous mentioned things (warm up regulator, blown air box, vacuum leak, fuel distributor, thermal switch). What it turned out to be was a bad oxygen sensor relay (the one right next to the ECU under the passenger seat). The relay is part of the frequency valve circuit. I had tested the frequency valve and it operated OK, and when I hooked up a dwell meter to the 'test port' I got a reading that seemed about correct. However, when I went through some of the trouble shooting steps for testing the ECU (James Weber's book "Solving Bosch Continuous Injection System Problems), the dwell reading wasn't changing like it was supposed to. I also noticed that there was no effect on the engine when I unplugged the frequency valve connector (with the engine running) .... when I did this on another SC, the engine practically dies immediately. I started looking at the wiring diagram and noticed that this relay was in the circuit and decided to check it before assuming the ECU was bad. I switched the relay from another 911SC and ... Eureka!!!!

Bill Gregory

Good news! Thanks for posting the solution.

fzr1k

i have been having very similar problems and found my relay is bad to but im still having problems. dead spot just off idle severe bog and cut out till 3000 rpm them a pop everyso often car idles great though