280Z no signal to the coil...

[MidnightCafe]

Hi gents,

 

I've been dealing with this issue for a few weeks now and I need your help. I just picked up my 1978 280Z last month and one day I came out to it and it wouldn't start. Ignition worked, starter turned over, but no spark. I am getting power to the coil, but no signal. What I've done so far is replace the fusible links with a maxi fuse block (all four fuses functioning properly). I've traced the lack of signal to the computer (transistor ignition module) which I've replaced, but still no signal. 

 

Is there a sensor I'm overlooking that indicates when the coil needs to fire? Crank position sensor maybe? What about ignition relays-what testing can I do to rule these out?

Thanks for the help!

[brodster]

I'm not very knowledgeable about the Z cars, but you should basically have the same EI black matchbox dizzy as the 4-cylinder version. Anyways, if you were to pop off the cap, there is a little six point star that spins inside a ring with six points. When the star spins it lines up with the points on the ring. Long story short, there is a coil and permanent magnet below that ring. Each time, the points line up, it changes the magnetic field produced by that permanent magnet. Then the coil detects that, and sends the pulse off to the black "matchbox". There should be two wires, green and red, that attach to the black box from the coil. This matchbox contains a very simple circuit with a power transistor, basically a solid state switch. This is what essentially opens and shorts the coil to produce your spark.

 

Since you replaced the black box module, you could start looking for other culprits. First I would make sure that the ignition module and coil are properly connected. Do you have a multimeter/volt meter?

 

Take voltage measurements at the coil + and - as well as the black brain box C and B terminals with everything connected. It may be hard to probe the C and B terminals with the plug on.

 

With the key in the on state, you should be getting a pretty close to battery voltage at the + terminal. Depending on the state of the brainbox module, you might see a couple of different voltages at the negative side of the coil.

 

At the B terminal of the black brain box, you should be getting "12+V". 

 

Another thing to check is your connection between the black box C terminal of the plug and the negative of the coil. First disconnect the plug from the black module. Switch your multimeter to Ohms, diode check, or continuity check. See if you have a connection between the plug terminal that connects to C and the negative of the coil.

 

Start with that. I would suspect that your module or coil isn't getting power. Once we know that, we trace back up the faulty line and see if a fuse is blown or something.

 

Also worth mentioning, since this is an old car, check all your ground connections. That never hurts and seems to be a culprit often.