PCM Wiring Problem

whiteout · June 15, 2004

Okay, this is actually for my parents 99' Astro Van with the 4.3L Vortec engine, but the basic idea should apply in any case.

The d**n van has been running like s**t for like close to 50k miles, and my parents have put close to $4000 into it trying to fix it. Basically every sensor on the thing has been replaced as well as plugs, wires, injectors, and a bunch of other stuff. It trips the codes P0300 and P0135. The first indicates a random misfire condition in all cylinders and the second indicates a faulty O2 sensor #2 heating circuit. So being pretty pissed off that mechanics are basically just throwing parts at it I decided to take things into my own hands today. I took everything apart that I needed to in order to gain accesss to the engine. The wiring on the O2 sensor looked fine, and it was just replaced, so I'm sure its fine. No codes are suggesting a vac leak and all the injectors are firing fine. Plus the thing has good compression on all cylinders (total PIA to check by the way). So at this point everything I read points to the PCM so I remove it thinking why not throw another couple bucks at it. Then I find it. There are four wiring harnesses leading to PCM and the one labled red has a major issue as it turns out. Upon inspection of the wire bundle leading to it there is a major chunk missing from at least one of the wires in the bundle (likely caused by abbraison by the looks of it), the coating appears to have been pink. My Haynes manual lists that the O2 sensors do indeed have a pink wire leading from the heating elements, but the wiring diagrams fail to explain which harness the O2 wires are bundled into (so basically I don't know if I have the correct pink wire since there are four harnesses labled red, blue, black, and white respectively). I really think this is the problem, but I have no way to verify it, any ideas??? And, can I safely splice in a new section of wire to repair the destroyed one?