questions: 240z to 280zx distributor with a twist

[Mikez31ss]

I bought a new '79 280zx distributor to replace my 240z dizzy. I also bought a GM HEI ignition module.

When I went out to install the new dizzy yesterday I discovered that a previous owner had removed the ballast resistor. That complicates the conversion a little since all the writeups I've saved included the ballast wiring as part of the conversion. And my conversion is a little different from those writeups because I'm planning on removing the E12-80 ignition "matchbox" and using the HEI module. I'm not sure exactly how crucial the ballast resistor wiring is in the conversion or how the PO bypassed it and what he did with the wiring.

I've modified a diagram from John Hull to show the way I think it should go but I want someone who understands the 240z ignition and electicals to look at the diagram and see if it looks right.

Edited February 18, 2010 by Mikez31ss
it needed editing

[Mikez31ss]

I bought a new '79 280zx distributor to replace my 240z dizzy. I also bought a GM HEI ignition module.

When I went out to install the new dizzy yesterday I discovered that a previous owner had removed the ballast resistor. That complicates the conversion a little since all the writeups I've saved included the ballast wiring as part of the conversion. And my conversion is a little different from those writeups because I'm planning on removing the E12-80 ignition "matchbox" and using the HEI module. I'm not sure exactly how crucial the ballast resistor wiring is in the conversion or how the PO bypassed it and what he did with the wiring.

I've modified a diagram from John Hull to show the way I think it should go but I want someone who understands the 240z ignition and electicals to look at the diagram and see if it looks right.

Ok I'll ask another question. Is there a particular source I should use for the vacuum advance? There are no vac ports on the Webers. Would I need a check valve?

[Zmanco]

The ballast resistor is only needed with mechanical points.

 

When I had triples I didn't use any vacuum advance as there isn't a good vacuum signal - the advance was all mechanical. That's one of the reasons why triples aren't known for good mileage . But the power and sound makes it worth it

 

Edit: I did add a nipple in the #6 runner for vacuum for the brake booster and it was adequate. The check valve is already part of the hose.

Edited February 21, 2010 by Zmanco

[Mikez31ss]

The ballast resistor is only needed with mechanical points.

When I had triples I didn't use any vacuum advance as there isn't a good vacuum signal - the advance was all mechanical. That's one of the reasons why triples aren't known for good mileage . But the power and sound makes it worth it

 

Edit: I did add a nipple in the #6 runner for vacuum for the brake booster and it was adequate. The check valve is already part of the hose.

Exactly, that's why I was surprised that it had been removed. The distributor and coil were stock 240z parts...only the resistor had been removed.

Two reasons why I asked. I don't have much faith in my understanding of electrical circuits so I made up that diagram to show my wiring. And since the tach has never worked, I was wondering if the tach function was lost because of the way the ballast resistor was removed and if there was some way to get it back.

On the vacuum advance... I feel like a dunce for not thinking of the brake booster. That looks to be the only vacuum operated part on the car.

Thanks for the help.

[Zmanco]

240Zs have a current triggered tach so it is wired in series with the coil and points. You should be able to get the tach working again by "splicing" it into the red wire in your drawing between the B terminal of the HEI and the + terminal of the coil. I don't know the colors of the wires in the harness to the tach offhand, but I do remember that the back of the tach has a white wire which is looped. This is the wire that needs to be spliced into the red wire I described above. I suppose you could just add 2 wires to the loop at the tach and pull them through the firewall and to attach to the coil and HEI.

 

Disclaimer: this is not how I have my car wired so I have not tried it, but don't see why it wouldn't work.

 

FYI, the resistor in the stock config is there to protect the coil/points so that if you leave the ignition on for a while with the engine stopped and in a postion where the points are closed that the coil doesn't overheat. It also limits the current across the points which helps them last longer. So not having the resistor wouldn't prevent the engine from running, but it wasn't a good idea either.

 

Edit: one more thing on the tach - if it didn't work with the points installed, the problem could be due to removing the ballast resistor, but it could also be that the tach is the problem. I went through 3 old tachs and eventually converted to a later 280z voltage triggered tach as I was able to find one that worked and was accurate.

Edited February 21, 2010 by Zmanco