GM Hei now no tach

[chiefmd]

Recently I decided to convert my 77 280Z transistor ignition over to the GM HEI module. I used my existing distributor and just removed the original transistor ignition and ballast resistor and installed the GM module. I used a Pertronix Flame Thrower II (.6 Ohms) coil. I followed instructions for connecting the wiring from the ballast resistor. Started the car and it ran great. The only problem is that the tach doesn't move unless I gun the engine and then it jumps up to 2-3k then just drops to zero. A member on another forum suggested removing the resistor located on the pax foot well. I disconnected it and installed a jumper wire. Same thing, car runs great just no tach. Any suggestion would be welcomed. Thanks

[alhbln]

I am not sure that the HEI module can manage the 0.6Ω Flame Thrower II coil without a ballast resistor, the switching current would be quite to high for the HEI module to handle.

Try introducing the ballast resistor inbetween the +12 wire and coil (+), does the tacho work then? Do you have a three or four wire tach?

[ChrisZ]

Adrian, it's a 280Z, he will have a 3 wire.

[alhbln]

Thanks, i missed that. Its still interesting to see the result with the ballast resistor added, this mod would lower the kickback voltage send to the tach.

[chiefmd]

I was thinking maybe just replace the .06 ohm coil with a Flamethrower 1.5 or 3.0 ohm unit? What do you think?

[alhbln]

A Flamethrower 3Ω coil should be safe. Try out the resistor in line with the Flamethrower II coil before you spend money. With the resistor in line you have a ~2Ω coil, that should be a good test to see if the tach works.

[chiefmd]

Just for giggles I hooked up a 1.5 Ohm Flamethrower that I had and the tach worked. So if I want to use the .6 ohm Flamethrower II looks like I need a 1 ohm resistor inline. Thanks for all the input.