I have a 01 LM7 that has been transplanted about 5 years ago and has been great. Cam, headers, and tune. I noticed a miss and was sure it was a coil or wire since it was not sparking #2 and all other good. I swapped with #4 and nothing changed. So, I got a wiring diagram for the coil, and I have 12 V key on, continuity to ground and checked IC wire from coil to ECM and perfect. So, I thought all it could be the coil driver in the ECM had failed. I got another ECM and had it flashed with my same tune and still no spark. I need help, really don't know what to do next. Thanks.

 

You need to load test the wires.

 

Would you explain further, how would I do that? The wires are probably 18-20 ga.

 

A wire could show low resistance/continuity but not be able to flow enough current and create a voltage drop either due to a bad connection or corrosion or most of the copper strands broken.

It would only take one good strand to show good power or ground on a meter or test light but once the current starts flowing it will get eaten up by said bad connection.

To load test I always use a head light bulb cause its bright enough you can tell when the circuit sucks as it will be dim.

So in this case you could use the head lamp bulb across the coil power and ground supply at the connector and see if it lights up bright.

You could also use your meter while a circuit is being used and measure the voltage to see if its dropping correctly at the load source. (Voltage drop test) you would backprobe at the connector the voltage should be battery voltage there. If say its only 7 volts then you know 5 volts or so of power are being eaten up by resistance somewhere. Also on the ground side should be zero volts if there is again say 7 volts there then resistance is on the ground side eating some of the voltage up

 

That I didn't consider. I guess I never thought of voltage drop on a signal wire (low amp) but a voltage drop test would answer the question. Don't know if I have a headlight bulb but I will find something. Plus I have 7 other examples to compare!!
I will let you know in a bit.

 

Ok I used a brake light bulb that has 1.1 ohms of resistance. Checked voltage key on 12.7 when I connected the bulb voltage went to 12.1 and it shows the same amount on #4 . I would think that's acceptable with that small of a wire.

 

That voltage drop is normal for a small wire with a load. You're good to go.

 

It was the spark plug on cylinder #2, I didn't know the ECM would turn off the IC signal if the plug died. Expensive lesson but got it going but I do have a backup ECM with my tune in it.