Coil issues

[dagold]

I 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.

[Zed Head]

Show or describe how you wired the HEI in.  It needs a good ground at the mounting grommets.

[dagold]

I am currently working in the eng8ne compartment but following Eurocrats guide. The catch is if I disconnect that and do number 6 on just the positive to the coil and a jumper shouldn’t I get a large spark?

Edited October 8, 2018 by dagold

[Zed Head]

 Actually, when you do Step #6, copied below, you're performing the function of the ignition module, but not using it.  So that step doesn't show anything about module wiring.  Unless you leave the module connected to coil (-), which can screw up the test because the coil (-) never really gets disconnected.

"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."

Any reason you can't just spin the motor with a spark plug on the valve cover?  You could even just use the coil center wire on the valve cover and you'll get a spark for every cylinder.  Take the other plugs out for more engine speed and more voltage.

[dagold]

sorry For the confusion, but that is what I am saying. I am not getting spark from the coil. I have everything but the black white strip wire disconnected and a jumper. If I turn the key to the on position I get +12v both sides of the coil. Tapping the jumper to a groom on the side of the car I get sparks at the ground but not from the HT lead with a spark plug connected. I didn’t think it was doing anything at al so grabbed it and I get a very small shock like touching a 9volt to younger if I ground to the body.

[Zed Head]

It might be that you're just not "tapping" hard enough or your jumper connections are weak.  The points and ignition modules have very solid grounds and contact points (think about how wide the contact areas of a set of points are) and make the connections and disconnections very rapidly.  If you're just brushing your grounding wire on a piece of metal you might not be getting a full charge through the coil.

Try a solid touch, make sure that current can flow, instead of a tap, and make sure your jumper connections are good enough to pass a lot of current.