DIY PROMDo It Yourself PROM chip burning help. No PROM begging. No PROMs for sale. No commercial exchange. Not a referral service.
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Just a quick question, I am just about to replace my pass side fan temp switch "located in the cly head " I purchased a stock replacement one 235 degrees i believe. My question is can i set the enable temp lower in the prom than the stock 235*? Or since this is a switch preset at that temp is this what i am stuck with? BTW this is a dual fan car the reason for the switch replacement was the headers melted the original connector and grounded out the fan causing a constant run condition. Thanks
Secondary fan speed should come on at 205 degrees than, its also about 20$ cheaper than what hoser companies nail u for for "lower engien temps" $35 repackaged part :-)
I do believe some have wired it into an unused pin in the ecm as well and made it work that way as well, I'm sure they will chime in.
I prefer the factory way of one controlled by each, little redundancy in case of failures never hurts in my eyes.
as 3.8transam alluded, the ECM does not control the 2nd fan at all in a 90-92 F-bod; so changing the on/off points (they ARE in the $8D calibration) will have no effect.
The corvettes using $8D DID have both fans under ECM control;so you can use the same pin as an $8D vette to control the fan #2 relay if you set it up the same way the vette wiring harness is set up.
There is also a wire in the ECM harness that is an input indicating when fan #2 is on - it can be Y'd into the fan#2 output pin to control the fan. I think there might have been some other slight detail to make this work - I don't remember, it's been years since I did it; but that's how I have mine set up.
According to this thread all thats needed is a second relay connected to the correct pin and you have two independently operating fans. Just have to change the control settings in the bin to whatever you want.
It's been a while since I did this, but you can also just swap the pins and then you can make your primary your "secondary" and your "secondary" your "primary", both controllable AND it's better for cooling as your A/C will now have a different fan since your secondary is now your primary (for temp control only).
Do a search on a post I made regarding cooling fans and the advantages of making your primary your secondary and vice versa. I mention how to do it. Just search for the article in the archives. I posted this sometime in 2004-2005.
