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Coil spark questions

Old 10-07-2018, 05:51 PM
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Join Date: Aug 2007
Location: Virginia
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Coil spark questions

have googled my brains out and tested everything I can think of but so confused at this point. The ballast resistor on my sons 77 280z started coming apart for some reason and he felt TIU was also going south do to random ignition problems. Short version is tried to direct wire in a GM HEI by passing the ballast. My current issue is I do not seem to be getting spark across the HT lead of the coil.

Trouble shooting I followed the below steps and on 6 getting a limited amount of voltage but not enough to cause spark. Feels like a 9volt bat to the toung at best. (2 coils same result.) if I am getting 12 volts at the + side of coil what would cause it not to fire?

There are some checks you should try before swapping too many parts.

1. Disconnect the plug at the TIU

2. Check the black wire is grounded.

3. With the ignition key ON, check for battery voltage at the Black/White striped wire.

4. Check the resistance across the red & green wies. Should be about 725ohms iirc.

5. Use the multi meter (analoge needle type works best) on low voltage setting (preferably lower than 5volt scale) and check for small voltage spikes across the red and green wires while cranking the engine. You should see 3 small voltages peaks per revolution.

6. Remove the HT lead from the distributor cap and connect it to a spare spark plug (or remove one from the engine).

a: Connect a jumper wire to the coil ( - ). Turn the key on and tap the junper wire rapidly on the car frame. You should see the spark plug sparking when you tap the wire. Be carefull for shocks from the coil.

b: You could also do this test through the blue wire and black ground wire at the TIU terminal block to check the blue wire works correctly.

7. Check coil resistance. It should be under 1.0 ohm across + & - terminals. Higher resistance can mess up the HEI unit.

If all these checks work out, then the HEI is not wired correctly of it is damaged. If you fry one, they sometimes come back to life, but not for long. So if you have any doubts about the module, I would change it.

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