rottweiler68

Have an '89 5.7 with dual cooling fans. I know the primary is controlled by the ECM and the secondary is controlled by the sensor near the back of block on passenger side. My question is with the secondary sensor disconnected, is it possible that the prom be programmed to control when the secondary fan comes on as well? Total newbie question with regard to programming as I have never done them on my own.

Thanks!

ULTM8Z

If it's anything like the 90-92 7730 ECM''s, you'll at least have to take that 2nd fan control wire from the sensor and wire it into the ECM (not sure what pin number for '89).

The 2nd thing is that the calibration mask you're running needs to have that functionality in it. Otherwise, no sense in doing the wiring mods.

I'm running my 2-speed fan that way... high-speed is wired into the ECM.

Tuned Performance

iTrader: (92)

C1 is the only ground relay control . For the ecm to control the secondary fan this ground control would need to be spliced onto .

rottweiler68

Thanks guys! Actually if i just ground the wire now the secondary fan doesn't come on, but i put it right to battery it does. So that's odd as well.

ULTM8Z

By "battery" I assume you mean the negative side... If it's turning on with the positive side, that would be extremely peculiar...

Also, where are you grounding the wire to when you do that grounding test?

rottweiler68

Yes the negative side of the battery is correct. What I call grounding is just touching the wire on the inside of the body, so that may not technically be grounding it