ecm forcing primary fan on when first started 8D
 

91 z28 running 8D mod, when i first start up the car the primary cooling fan kicks on after about 2 seconds, and randomly shuts off for a few seconds then back on, it does this numerous times for like 4 minutes, then stops and then starts operating normally with fan on/off temperatures. i've had the car so long i cant remember if its did this when the car was stock or after i started tuning. im getting ground signal out of the ecm on pin b8 green/white wire that triggers the fan relay. i've disconnected all the ecm inputs that i can think of that can trigger this signal out (a/c pressure switch, coolant sensor) and it still does it. im thinking there is something in the tune that is causing this thats either on a timer or temperature related. i found a related thread saying the fix had to do with bit5 fan, but that applied maf bins. anyone have an idea?

Re: ecm forcing primary fan on when first started 8D
 

have you tried the stock calibration to see if the problem disappears?

Re: ecm forcing primary fan on when first started 8D
 

No I have not tried the stock calibration, I did use it as a compare bin and cannot find anything that would cause this problem

Re: ecm forcing primary fan on when first started 8D
 

Well, the problem is either hardware or software... we can easily rule out the software by trying out the stock chip. In cases like these you have to be as methodical as possible.

Meantime, can also send me your bin if you want and I can take a look as well... ultm8z@yahoo.com

Re: ecm forcing primary fan on when first started 8D
 

ECM may be going bad. Pop the top cover off and start the engine. Gently press on various areas of the board and see if the issue comes and goes.

RBob.

Re: ecm forcing primary fan on when first started 8D
 

tried stock bin, same thing. tried with chip adapter and chip removed, same thing. tried pressing on the board and lightly tapping the ecm case with no changes.

Re: ecm forcing primary fan on when first started 8D
 

if you've verified the ECM is actually sending out a ground signal when the fan comes on, then that rules out an issue with the fan relay.

only other thing to try would be another ECM is you have a spare.

Re: ecm forcing primary fan on when first started 8D
 

I'm thinking I will try another ecm eventually, I don't have one on hand so I want to try further diagnosing. Do you know what other inputs that the ecm uses to control the cooling fan?

Re: ecm forcing primary fan on when first started 8D
 

re-read the original post...

assuming you're 100% positive it's the primary fan...

the cooling fan switch has nothing to do with the primary fan.

in which case a malfunctioning coolant sensor (not the switch) can fool the ECM into turning on the fan if the sensor resistance spiking abnormally. if you have access to a scanner, keep an eye on the coolant temperature readout to see if it matches the dash gauge... or if its spiking up to higher temperatures when the fan comes on...

Re: ecm forcing primary fan on when first started 8D
 

i am 100% positive its the primary cooling fan (driver side) thats controlled by the ecm, i mis-spoke in my original post i meant coolant sensor, not cooling fan switch, also to make sure i was working on the correct circuit i grounded the fan switch and the secondary fan came on as designed. i did a little more verifying on the problem, and it seems as tho it is timer based not temperature related. i turned the ignition on and engine off, fan does it problem thing for about 4 minutes, i leave the ignition on for another 15 minutes and it doesnt do it again. cycle key off for 5 seconds and then back on, and the fan starts doing the same thing. i do have a scan tool, but when im live streaming it loses connection as soon as that fan turns on, don't know if its related to a voltage drop or if its an ecm failure.

Re: ecm forcing primary fan on when first started 8D
 

that's starting to sound very ECM related.

Re: ecm forcing primary fan on when first started 8D
 

borrowed an ecm from my dads parts car, works good now. thanks for the help.