IMRC question

I have had to repair the IMRC (Behind the alternator) on my 98 winnie. Everything I read on this forum about the actuactor opening at 2900 RPM is what I have the question about. I know in the haynes manual this is what it says also. But....in the Ford factory service manual it says 1500 RPM is when the vaccum cuts off and they open. I have actually watched mine in operation the same time I am watching a Tach and sure enough mine open at 1400 RPM (close enough to 1500). I also got to thinking and I was wondering when the last time was I ran the engine up to 2900 RPM and the answer is very seldom or never......I know at 70 MPH the engine runs about 2100 RPM so this means they would never open for me. So I know 1500 RPM to be the point where they open on the 98' 3.8 L.....is it true with the rest of them.....all we can do is watch them to find out if this is true. Enquiring minds want to know........:dunno:

I have not monitored mine close enough to know.
I think that mine kick in at a higher RPM from the extra power that I get at that time.
The idea is for them to stay closed, and open only under hard accelleration, like when you are passing.
I do not think that the intention is for them to be open when you are cruising along at 55 - 70 MPH.
So there may be other factors involved in their opening than just RPM for the situation where they open at the lower RPM.
I have not rev'd up my engine like that in the driveway to watch mine.....as (knock on wood) I have had no issue with mine.

They are open with the engine OFF, and close when the engine is started....and that is as far as I have had to worry.
If one of the actuators does not work, or something is binding or catching....you will find it with that test.

HI
I don't doubt your findings in that you have watched the tach and noted when they open. FWIW, I have been running my '96 with my "front" IMRC wire tied to the closed position and vacuum unhooked and plugged for quite some time now. I have the electrical hooked up so I should have triggered a CEL by now for IMRC failed closed had the PCM commanded it to open. So, I think my system is looking for much higher RPM (2900) before commanding it open. Perhaps they re-engineered the system a bit for '98.

I watched mine on my 96 and they opened at about 2800 rpm. Much like vacume operated secondarys on a carberated system. It has to do with power range as Wiswin said heavy acceleration like passing on the highway. Im not sure why yours is so low maybe they geared the van differently in 98.