Well, I can share a few thoughts. If the Check Engine light is not coming on, you can probably rule out things that are monitored by the Engine Computer. For the most part, that leaves fuel delivery and the charging system. Also, before 1996, cylinder misfires aren't detected either so you could have a loss of spark problem due to a computer output circuit. The ignition coil and wiring to it would be likely suspects.
What you might have to do is connect a wire to a known point in a circuit and run it inside the car where you can connect it to your voltmeter so you can monitor it while driving. You might find the supply voltage disappearing to the fuel pump, ignition coil, or even a sensor.
I'm not real familiar with GM service manuals but the Chrysler ones do a real good job of showing where wiring harnesses run. I'm a big proponent of manufacturer's service manuals over the aftermarket stuff and especially any data on a computer. Harness diagrams usually show the locations of connectors and splices. You can use that information to figure out which wires are running behind the engine. That will give you some ideas on which wires to monitor with your voltmeter. I made a box once with a dozen leds and resistors that I could connect to a dozen different places to monitor. Only used it once and I accidentally found the problem while trying to make the connections.
If you find the intermittent circuit this way, you might be able to run a new wire. One thing I always pounded into my students was it is not acceptable, (on a customer's car), to just run a new wire for a couple of reasons. If they don't find the break or place it is grounded, why did it happen and will it happen again? If a wire got cut from rubbing on a sharp metal bracket, which circuit will be affected next when the next wire in the harness rubs through? Maybe your power locks stop working intermittently now, but that next wire might kill the engine in the bad part of town or out on a deserted highway. Finding this type of problem will result in repairing the mounting hardware that let the harness fall onto the metal bracket or hot exhaust manifold before it can affect the next wire. The second thing is if the problem is intermittent, and the wire is grounding out, running a new wire won't remove the intermittent short. You have to cut the original wire out of the circuit at both ends. In some case, there could be a whole bunch of wires that connect at a hidden splice. Every one of those wires would have to be cut out of the circuit before running all new wires. It is almost always faster and easier to find the location of the short. If a splice is corroded, it might cause a loss of power to only one item. Think of four tail lights / front running lights all connected together in a splice. Suppose the right rear light stops working because its wire corroded off of the splice. You could run a new wire from the switch to that one light and all four would work. But eventually that splice would corrode some more and the second light would stop working. Now you have to do the job all over again for the second light. Had you found the corroded splice originally, the second problem never would have occurred.
While I talked a lot about splices, loose, stretched, or corroded connector pins are a lot more common. That's what I would look for first when you wiggle stuff.
Tuesday, June 29th, 2010 AT 6:37 PM