topspin

On my 96 LT-1, Ihave 4 wires to the ignition module connector, one is groun, with connector unpluged the ground wire reads grounded with ignition key off but when I turn ignition key on the wire still reads grounded. So my question is : Should this wire not read grounded with key switched to on position ? I feel this is why my ignition coil is not firing. Or maybe my crank sensor is bad because the last time it ran I noticed the Tach didnot work? I have 12volts at ignition module on two wires with key in on position.

MikeC4

Here is some testing you can do(see highlighted for your case, it seems that you have correct 12V at two connector terminals, as long as they are "A" and "D", each with respect to ground). Refer to this diagram:



Disconnect the ICM connector. Leave coil connected.
Turn key to ON.
Check for dc voltage with a digital meter at harness terminal "A" to ground and and also "D" to ground. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM.
Result should be 10v dc or more on both terminals. If you get no voltage, use the diagram and chase back toward the coil and the ignition fuse. Power for the ICM comes from the ignition fuse and through the coil, so any of that could be bad.
If you have good voltage, switch the meter to ac scale and connect test leads to terminal "B" and to ground. Observe meter while cranking the engine. You should see between 1 and 4 volts ac (those are the pulses that trigger the coil to fire).

If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between. Visually inspect all the connections you can get to for poor contact or corrosion.

The above procedure was borrowed from:
http://shbox.com/1/4th_gen_tech2.html

jfb

The black ground wire is grounded all the time, the ign sw is not involved. No tach signal is a reasonable sign that you have lost the crank position signal and without it, no spark is possible.