Just putting this "out there" in the hope that others won't fall into the same "trap" I did.

Long story, (hopefully?), made short/shorter:

Trying to "tune" my new 396 LT1 engine combo (See signature). Bought an AEM wideband O2 sensor to help with tuning. Since I had already deleted all evidence of A/C on my car, I "looped" the 0-5v AEM output signal from the wideband gauge, to the high pressure sensor input of my A/C system, so ..... that I could datalog my engine air/fuel ratio through the "A/C volts" Scan94/95 channel while tuning.

Sounds good so far, right?

And here's where the "Law Of Unintended Consequences" comes into play. My PCM, apparently, is "thinking", (for want of a better term), that the voltage signal now being supplied by the wideband gauge is "reporting" A/C line pressures in the 300-450 psi range, and, of course ...... is turning/commanding "On" both cooling fans!

I've "worked around" this problem (?) by installing a simple (manual) On/Off switch in the 0-5v circuit from the wideband gauge to the A/C pressure sensor, so that when not data-logging AFR, I can avoid having both fans running continuously during driving.

Tuning Scoreboard: LT1 PCM - 1 and Human DIY Tuner - 0