As I came back from lunch the other day, I was met by our dispatcher who was grinning from ear to ear. “You’re going to love this one”, he says…. Suddenly, that burrito gained about five pounds in my stomach. I just don’t need another headache….
The repair order had two lines on it and only one is for me. “Battery won’t stay charged”, well heck, it doesn’t sound that bad; there must be a catch <g>. The other line was for an erratic trans shift and clunking.
Driving the 94 Buick into my stall, I noticed that the trans was shifting very erratically and the headlights were dimming every 5 seconds for just a moment or so. I could hear the alternator charging and then stop for a moment and the lights would dim. This cycle would repeat endlessly.
The alternator on this vehicle has only two wires going to it. The 10-gauge B+ wire and the enable wire to terminal L of the regulator. Not wanting to waste my GMM batteries on such a simple repair, I whipped out my jippo DMM and made some quick tests. Both the B+ and enable (terminal L) wires were sitting right around 12.0v.
Considering the erratic trans shift (controlled by PCM) I thought it wise to check the PCM grounds on the front of the engine. No problem there… There was also no excessive voltage drops from the alternator B+ and ground to the battery positive and ground. The alternator and the transmission had also just been replaced with GM parts.
Strange…. I’ve got an alternator that quits charging for a moment every 5 seconds or so with no bad grounds and 12v to the enable wire (internal regulator). Sounds like a bad alternator, right? Yeah, right…. <g>