Wiring
Posted: Mon Sep 26, 2011 9:42 am
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.
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.