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Old 03-19-2018, 11:01 PM   #6
dayj1
Senior Member
 
Join Date: Jul 2009
Location: Athens, AL
Posts: 499
Re: PCM is not grounding fans properly

Quote:
Originally Posted by jrpontiac View Post
I posted this in the electrical forum as well.

I am working of the relay setup for my engine fans on my LS conversion. I got a dual fan setup with each fan triggered by a relay that is activated by the engine PCM. Each fan has it's own relay. The PCM activates the fan relay by triggering the ground to the relay. My problem is that when the pcm triggers the fan (about 190degrees) that fan only runs 1/2 speed, maybe less. The relay is also rapidly clicking, both relays do this. When I bypass the PCM ground with a wire clipped to a solid ground the fans run at 100% and the relays don't click.

So I assuming I have a grounding issue, my problem is I don't know how to improve the ground since it terminates somewhere in the PCM.

The fans have their own ground, which I believe is adequate because when I activate the relay by grounding it to the neg battery post the fans work great. When I let the relay be activated by the pcm ground switch the fans don't work so great.


Any suggestions?
What engine did you swap? Also, what year?

Quote:
Originally Posted by racecougar View Post
Had the exact same problem with the high speed fan output on my EEC. Low speed works perfectly. I ended up triggering the high speed relay via a switch that overrides the low speed relay (and I have yet to need to use it; the fan cools the engine adequately using just the low speed). I would be interested to hear if you find a solution, as I'd love to have the EEC properly control both speeds.
Same question. What engine (and year)?
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