Ok.... I finally got all of my software / hardware working and actually made a prom that works! I have an 85' TPI z28 w/ a T5 that I converted to 89' plenum, runners, fuel rail, and TB. I am now also running a '165 ecm. For the bin, I am using ANYX ('89 formula 305 w/ 5 spd) as my starting point. All I have changed is the fan 1 turn on temps, disabled EGR, and VATS. When I first burned it, the fan was on constantly. Then I unchecked "cooling fan N/O req input" and the fan wont come on at all? The fan would not turn on with the stock '87 memcal I was using before either (ABUN) Am I missing something? Is it a problem that I still have the single fan setup that came in my '85 tpi? This thing is running better than ever aside from this fan issue! Any help would be great

ECM only turns on one fan whether you have 1, or 2.

alright, then the single fan is not the issue. Any ideas as what is?

Check to see if ECM will set a DTC when coolant sensor is disconnected.

i think i've read that some of the older ecm's used a ground to turn on the relay and some of the newer ones used +12v.(or the other way around) so you will have to do a search, but if thats what it is, you just need to switch 1 wire on the relay.

DTC?

diagnostic trouble code. His thought process is the coolant temperature sensor (cts) may not be sending back proper information to the computer for the fan to turn on. In other words it may be pegged in the cold position or such.

at least thats how i read in to it.

if memory serves me correct, when the cts reads 212*F,the fan should kick on.

if it was me i'd check to make sure i have power down to the fan pigtail when coolant temperature is over 212. If not suspect a relay or wiring problem.

I really just need to get my damn aldl cable working so I can see what the computer is thinking.

Hopefully you have not given up.

A paperclip across the correct 2 pins of the ALDL connector will flash any DTC's on the SES light. Do a search for details. No ALDL cable needed to answer that question at least. Emissions-affecting DTCs manifest as a lit SES light. A bad checksum will commonly fire the fan and the SES light- among other things...(hex "AA" is the code for experimental mode btw- look that up too if you're not familiar sometimes it is useful) but you say the car is running well so either your SES bulb is out and your limp-mode is exceptional, or your method for testing the fan logic for N/O is flawed. Try setting the fan trip point to a value well below stock (maybe 90) and wait to see if it changes state after an idle period. Warm up enough for the stat to open at least... or take the sensor out and drop it in 110 degree water from the tap.

when looking under the dash it will be the top two to the passenger side of the dash
flip key on and count the number of flashes there should be one pause two flashes and repeat three times then your codes come after that when codes are finished the code 12 will flash again 3 times.

Nope, haven given up. Just busy moving, buying a house and starting a new job. Thanks for the help. The problem is not the fan itself. I tried diagnostic mode long ago, and it turns on. I am begining to think that the problem is in the switch wiring.