Bumping this thread again.
I went out and bought an OBD1 ALDL cord and got the WindALDL scanning software. Really cool logging, display, and analysis tool for only $60.
Anyway, I digress... everything looks in range except the O2 sensor values are kind of strange.
The scanner is displaying about 0.455v +/- 0.005v. Never any voltages outside of that range which is suspicious.
So I parked the truck, disconnected the sensor, probed the sensor lead to ground, ~0.8v with fluctuations of about 0.2v. Weird that its reading something different from the scanner but seems normal given it was disconnected. So, I probe the harness side, 1.48v. Double weird. Look back at the scanner, STILL 0.455v!!! TRIPLE WEIRD. So I think its gotta be a wiring problem, right? Completely ripped up the O2 wire all the way back to the ECM, no damage to the wire, still reading 1.48v on the harness side. Okay, ECM grounds gotta be bad, right? Nope, everything checks out on that side too. Next trick I researched was to jumper the O2 harness side to ground giving the computer a simulated lean condition. No change at all.
So I've come to the conclusion the ECM is bad..... But how? The truck runs pretty good aside from this code 13 sets only about once a week.
Anyone have any thoughts? Any other things to test?
Any help would be greatly appreciated.