Originally Posted by
amrg
I havent checked here for a very long time but I came back because my SS fan is having issues. I have the the SS 850W fan running puller and the C7 600Watt as a pusher, both using the same signal wire. 3 days ago the SS fan stopped working properly. I noticed that it would do the kick which it normally does when it first wants to start, spin 1 revolution then stop. No idea whats wrong here. The other fan is running as normal. I only realized this issue since the other fan is noisy and it had to run at a higher speed to compensate for the puller not working.
But to give some input here, Brent posted the logic of the Spal fans (GM vs aftermarket) which are opposite to each other. GM uses 0-90 which is AFtermarket 90-0.
With an Oem ecu and the aftermarket version of the fans, the PWM signal sent by the ECU to the fan is done by slowly ramping it up and down. So if you command 90%, its not immediately 90%. on my E67, it takes 10 seconds for the signal sent by the ECU to go from 0% to 90%. This results in a cat & mouse effect during startup (and if you have the fan deactivate at speed option).
For cpd004, when your coolant temp hit 199.4, the ecu starts sending a signal. As it ramps it up, the ECU sends it as 5%,10%,15% ----> 80%, 85% , which the fan interprets inversely as 95%,90%,85% ----> 20%, 15%, and this is why your fan ramps up then slows down (it probably ramps up to 50% speed by the time the ecu is now outputing 50%).
Nothing can be done to solve this on a GM ecu. If you're using a holley ecu I believe, you can actually change the output signal from PWM + to PWM -, which is basically a signal and its inverse.