1983Chimaera

Car is a fairly stock 1988 IROC-Z, LB9 TPI 305 with dual factory fan setup. A/C compressor is currently deleted, all A/C system wiring connections remain except for compressor clutch connector (unplugged). Alternator has been changed to an AD244 using only the tan/white stripe "F" field voltage wire and red "S" voltage sense wire. Wiring is otherwise stock and all connections/grounds/proper voltages present. The primary cooling fan is engaging (on) at initial engine startup (once the engine actually fires, not key-on engine-off or during cranking). After driving over 35+ mph the primary fan disengages (off) and remains off. If car is restarted at operating temp or above primary fan remains off. Secondary fan operation is unaffected, appears to work properly. Car maintains proper temperature, shows no sign of overheating. ALDL diagnostic mode triggers fan properly, only code presented is 12 (normal). No other trouble codes present, SES does not trigger otherwise. A/C head unit operation does not trigger the primary fan in any setting, nor the secondary fan. I have tried putting a wire in the end of the A/C high pressure switch to short it, and this only triggers the secondary fan (key-on engine-off). Manually triggering the primary fan works (green/white stripe wire shorted to ground), and have confirmed relay proper operation. My only theory is that somehow the ECM is not grounding the primary fan at the proper temperature. I have tried disconnecting the secondary fan and letting the temps rise, but primary fan does not engage after the initial operation at startup. I have also tried different coolant temp sensors with no change. Disconnecting the CTS with engine running results in very poor/erratic idle, so it is sending signal.

I have been through every wiring diagram I can find, all the relevant ones on Austin Thirdgen (great reference!), Haynes manuals, and even tried researching in C4 Corvette forums (similar setup). I've seen a few threads about the dual fan primary running at startup, but they were no help ultimately in my situation. I have seen reference to pre-87 cars with A/C delete needing to short to ground the ECM A/C input for proper fan operation, but the 88-up cars using a different setup. I know the ECM looks for A/C compressor clutch engagement before sending the fan signal. On the 88-up cars it grounds in the ECM however, so it's looking for an input signal, not an external ground. I hate to throw money at an ECM just find out it wasn't the problem, especially since it's a non-returnable item. Car runs strong otherwise, engine is a fresh rebuild, no other issues. I do not want to install manual switches or aftermarket fan controllers, looking to regain stock fan operation. Thoughts? Comments? Rude gestures?

Bobby Suth

iTrader: (2)

Sounds like what my 89 formula is doing