MSefi.com read only forum (Jan.15,2018)

I wish I had a recording of this but... About 3 or 4 minutes after a cold start (-20 to -10 C) at low rpm (maybe higher but the Jeep is too noisy) a high pitched whistle that slowly lowers in pitch then disappears after 10 seconds. It only does it when it is cold out.

Maybe this should be in the "MS-II Ignition Setup, Tuning, and Troubleshooting" section but I think this is "Air Supply".

Has anyone experienced this? Other than this "bomb dropping sound" the setup has been running perfectly.

Any ideas?

Thanks, Jim

Jim,

Have you done anything to try and determine the source of the noise?

As you think it's "air supply": I have a Ford PWM IAC that made a noise for awhile after start up. I increased the PWM frequency from the default to a higher value and the noise stopped.

Hello 66fb,

Yes, I've stood there in the cold and mud waiting waiting... no whistle. Get in the Jeep and then there we go! It has stopped now that it has warmed up but I thought I would ask and see if anyone else had this going on. I do have the coolant lines removed from the TPI throttle body and it could be something like venturi icing going through or around the IAC. It only would do it, it seems, during only one kind climactic conditions... About -10 C and dew point at the same temp.

Maybe the diaphragm in the fuel reg is going! I can't/haven't figured it out yet.

Thank you,

Jim

Sounds like the IAC to me.