Fan 2 cycles on and off then on then off.
 

I finally got my LM7 running, just got the ECM flash on sunday. but when the engine heats up to fan 2 on setpoint it cycles on and off constantly.

my engine is a 2000 GMC 5.3L LM7 stock, but not using clutch fans, using dual electric fans run off the ECM.

now from the HP tuner software i can manually run each fan and it does fine.
so i am fairly sure the wiring is ok. it has to be a setting in the ECM.

any help would greatly be appriciated.

Re: Fan 2 cycles on and off then on then off.
 

I would try turning your fan 2 off temp down a bit more than it is.

Re: Fan 2 cycles on and off then on then off.
 

ok can try that, maybe i also saw something once i posted it.

does the ac disable fan 2 at mph have anything to do with it?

Re: Fan 2 cycles on and off then on then off.
 

Well, this may be a weird analogy but home furnaces (blowers) will short cycle (on and off cycles) if the ON and OFF point are too close together; I'd have no reason to thing these wouldn't work the same way.

Re: Fan 2 cycles on and off then on then off.
 

i changed the AC enable and disable psi to 500
and changed Recirc Option to fan #2

and it fixed it, yeah!!!!!