Fan 2 cycles on and off then on then off. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mrhurt73 · 04-09-2013, 08:28 AM

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.

ls1nova71 · 04-09-2013, 11:15 AM

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

mrhurt73 · 04-09-2013, 11:40 AM

Quote:

Originally Posted by ls1nova71

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

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?

BR3W CITY · 04-09-2013, 02:24 PM

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.

mrhurt73 · 05-03-2013, 10:05 AM

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

and it fixed it, yeah!!!!!

04-09-2013, 08:28 AM	#1
mrhurt73 Registered User Join Date: Aug 2012 Location: clifton forge, va Posts: 261	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. Attached Images __________________ My Projects- http://67-72chevytrucks.com/vboard/s...d.php?t=557301 Quest for Hot Rod Power Tour 2013. http://67-72chevytrucks.com/vboard/s...d.php?t=543735 my 85 GMC 2wd to 4wd conversion for the wife.

04-09-2013, 02:24 PM	#4
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	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. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

05-03-2013, 10:05 AM	#5
mrhurt73 Registered User Join Date: Aug 2012 Location: clifton forge, va Posts: 261	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!!!!! __________________ My Projects- http://67-72chevytrucks.com/vboard/s...d.php?t=557301 Quest for Hot Rod Power Tour 2013. http://67-72chevytrucks.com/vboard/s...d.php?t=543735 my 85 GMC 2wd to 4wd conversion for the wife.

04-09-2013, 11:15 AM	#2
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	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. __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html



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