No start. Wire harness problem?

[davidsmith]

Just a little more info I dug up.
The ground for the distributor is through it's mechanical connection to the engine block. The module gets it's ground through its mounting screws and being in contact with the metal inside the distributor body.

When you installed the new module, did you check the gap between one of the reluctor "ears" on the rotor shaft and the adjustable pick-up in the module? It should be 0.008" to 0.010" (roughly the thickness of three layers of 20# bond printer paper).


With the ignition on (but engine not cranking), check the voltage at the (-) terminal of the coil (the one where the black wire from the module is connected). It SHOULD read the same as what you measure at the (+) terminal (purple wire). If the voltage reads something like a couple volts, bump the key a bit to make sure one of the reluctor ears is not right next to the pickup and see if it comes up. If it stays low, the module is probably bad.

With an ohmmeter set to its lowest range (usually 200 ohms), measure the resistance from the metal shell of the electronics module, inside the distributor, to a good ground on the engine block. It should measure no more than the value you get when you touch the test leads together (maybe 0.1 - 0.2 ohms higher, but not any more than that).

If you have a 12V test light, connect the ground clip lead to a good engine ground and put the probe tip on the (-) terminal of the coil. With the ignition on but engine not cranking, the light should light. When the engine is cranking, the test light should flicker a bit as the module pulses the (-) side of the coil. Also, as I mentioned before, your tach should indicate the cranking RPM which should be in the 200 - 400 RPM range - it gets its signal from the (-) side of the coil and the distributor module.

If the test light doesn't flicker when the engine is cranking, it sounds like the new module is not working either. There is nothing else in the distributor that should need replacing nor do you need to spend the $$$ for a new one. It is possible (although unlikely) that the replacement module was bad or something else in the electrical system has gone belly up.

If you have a poor connection, in the purple ignition circuit, somewhere between the ignition switch and the coil, you may still measure 12V at the (+) terminal of the coil, with the key on, because there is no load on the system. When the module tries to pull down the (-) terminal, the voltage on the (+) terminal may get dragged down due to the high circuit resistance. Check the 8-pin connector between the instrument panel and the engine to see if it's not corroded.

One other test you can do is to disconnect the black wire, between the module and the coil, from the coil and connect a test light between the open black wire and +12V. The light should be OFF, initially but when you crank the engine, it should flicker. If it does, the module is doing its job.

[Big D]

David, the diagram in your link isn't the one being used is it? That looks like the shift assist module used to interupt the ignition circuit to allow shifting into neutral in a stern drive application, hence the blue wire for the shift switch.

Based on Unchained's last post, I'd check the position of the distributor. If it's been removed, I have a feeling it didn't go back in properly. Happens more often than you think. And the fact that it ran for 5 minutes doesn't really rule this possibility out. I'd start from scratch. Bring #1 cylinder up to top dead center on compression stroke then make sure the rotor is set to fire #1 cylinder. Follow the plug wire and make sure it's going to #1 plug. Then follow all the other wires making sure they correspond to the correct firing order sequence and are going to the correct plug. Eliminate this possibility before moving on and replacing more parts.

[davidsmith]

I believe you are right about the diagram but im not sure the distributor index has anything to do with weak spark. It would still spark strong if it were only out one tooth. He said he was fighting a weak spark and low voltage so I was looking at reasons for that.

[Big D]

I thought you might have known something about his hardware that wasn't passed on to us so the ESA module threw me off. Don't blame you for going after the weak spark thing but I've found "weak spark" to be somewhat subjective. What one considers a weak spark may be just fine to someone else and visa versa. So I've kind of learned to take that observation lightly. I've just seen too many distributors put back incorrectly to not mention it now. You're right on about the gap measurement, deffinately needs to be confirmed before moving on.

[Unchained]

Ok guys, I guess what I thought was a weak spark was actually ok after all. I replaced the entire harness and pretty much every component in the ignition system, except the distributor itself. The main problem was water in my gas tank. The gasket at the fill cap was dry and cracked and water must have been leaking right in. I have two water separators and both were full of water and bad gas that was yellow and full of debris. I removed all of the plugs and cranked out all of the water out of the cylinders, then hooked up to my port tank and she fired right up.
I hope this post helps someone out. Would have saved me a lot of time and money. All of the parts I replaced looked orignal so I guess it wasn't a total waste. Hoping for a trouble-free season next year. Thanks to all for your help.
Mike