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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Yeah, I set Fan 2 (the high speed setting) come on at 10°C higher than the low speed. It's basically there in case the low speed becomes insufficient for the given conditions.
BTW, this isn't something I discovered. I found out about it in a search on this forum and decided to give it a shot with my new Taurus fan. Figured it'd be way cleaner than running it off a temp switch.
Running second fans on the temp switch was so you could retain a fan even if the ECM craps out. Might want to put an even higher temp switch in parrallel with the ECM to retain that safety. Just in case or like myself and half the others, just keep a spare ECM in the car
On my 91 I left the temp switch operational and di the wiring change and now have both - ECM controlled 2nd fan and the fall back to the temp switch if something else fails.
Need to start carrying that old 730 on the shelf in the car just in case. I do carry a recent chip in case the emulator ever decides to give up.....
Running second fans on the temp switch was so you could retain a fan even if the ECM craps out. Might want to put an even higher temp switch in parrallel with the ECM to retain that safety. Just in case or like myself and half the others, just keep a spare ECM in the car
You can also WIRE-OR the mechanical switch with the 2nd ECM output for the fan. That way, the fan will work if either one fails. The good of part having the ECM control (or help control) the 2nd fan is that you can add a toggle switch in the car (and a few lines of code) to force the fan on which works well when sitting in long staging lanes at the track.
EDIT: The WIRE-OR means connecting two wires together that operate on the "ground side". That is, the mech. switch provides a ground to the fan relay and the ECM provides a ground to the fan relay. Therefore, you can tie them together and either one will activate the fan. Ensure that your fan is wired properly before attempting the connection. If it is improperly wired then this setup will not work.
I also changed the parameters so the Second Fan became my Primary Fan. This way, when I turn on the A/C, it provides better cooling.
Also, for "emergency", you can always wire a manual switch in parallel. But of if the ECM takes a crap, you probably aren't going anywhere anyway. And if you do, when you have codes, the fan comes on automatically anyway. There is no real reason to keep the temp switch based on the ECM taking a crap.
