I am using a stand-alone computer (Wolf). I've also retained the factory ECU to control other things like the oil metering pump, AC, etc. Everything works great.....except for the air pump and low-speed fan operation. When the engine is cold, the air pump works fine. After it's warmed up and air (from air pump) is by-passed (the one that causes mooooing sound) for a split second, the air pump cuts off.
Then, it comes on again for about 5 seconds, then cut off. The process would repeat forever if I just let it sit there and dle. It seems like it doesn't want to channel air through the by-pass. The service manual says that the air pump should continously work upto 3250 RPM. What is going on? I've thought about removing the airpump, but how
long will my high-flow cat last?

The low-speed fan has simliar symptom. It cuts on for about 3 seconds, then cut off. On, off. On, off. I have to use medium-speed (fan mod) to cool it down, which works fine. I'm not as concerned about this as
the air pump not working right.

My hypothesis for this is the factory ECU doesn't "see" the injector and igniter anymore, therefore an open circuit in the ECU causes the intermittent operation of the fans and airpump. What do you think?

 

CHECK YOUR PM.
DAN

 

how does RPM affects their operation?