Removing a generator or a starter from the engine is the worst and least effective way to test them. You got that advice from a parts salesman, not a mechanic. Test benches have up to one horsepower motors to run generators. They can not possibly run them wide open to test them for maximum current output. That takes from five to eight horsepower, and that test is especially important on the very poorly-designed GM generators. They develop huge voltage spikes that can destroy its internal diodes and voltage regulator. With one defective diode of the six, you will only get exactly one third of the unit's rated current, and that is not enough to run the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over hours or days. You need a professional load tester with the generator being run by the car's engine to test for maximum output current and "ripple" voltage, both indicators of a bad diode. A generator with a bad diode will still produce some current, and output voltage will be close to correct, so the unit will falsely appear to be good on a test bench.
Off the engine a starter spinning freely will draw less than 50 amps. Any tired old starter can do that. You need to test it under load when it's trying to crank the engine. During that test Chrysler starters will draw around 150 amps. Most others will draw around 200 amps, ... Even more on older V-8 engines.
You are getting no response at all from the starter. A weak battery, or a battery that is run down due to a defective generator will not cause that. Those will cause slow cranking or a rapid clicking / buzzing noise. Starting normally after an hour and a half proves the battery is still okay. It didn't magically fix itself. And the generator is not the cause of this issue because it isn't even in the picture yet until after the engine is running.
Starters CAN be intermittent but that is not real common and it doesn't stay in the condition for long before it fails completely. Your mechanic can perform one starter test on the car to see how much current it draws, but the results will be of no use to you. We know it's not dragging and drawing excessive current because it does crank the engine normally when the system works. It is more likely there is an intermittent problem in the control circuit, meaning the ignition switch, starter relay, and neutral safety switch. That is a low-current circuit but it has more parts than the high-current starter circuit, and it is responsible for a lot more problems. Starter testers do not test anything in that low-current circuit.
There's two relatively common things you can try yourself. First try cranking the engine with the transmission shifted to "neutral" or after shifting out of and back into "park". If that works, suspect the neutral safety switch. Next, follow the smaller positive battery wire to the under-hood fuse box and be sure that connection is clean and tight. Those work lose on a lot of car models and cause intermittently dead electrical systems.
Any further testing has to be done while the problem is occurring. As long as the entire starter system is dead, (not just cranking too slowly), and everything else is working, the system can be broken down into four parts, and each one has a test point at the starter relay socket. If you find anything else is also dead, like any lights, the radio, power windows, etc, you don't have a starter system problem. You have some other electrical problem that includes the starter system. Spending time in the starter circuit in that case is a waste of time.
Saturday, January 11th, 2014 AT 12:52 AM