ignition problem

[Kennymonster]

Thanks for the information Steve.

With MSD setup I believe a ballast resistor is not necessary, at least that's what I read. The 9.8 was measured when the new battery was first swapped in.

I will go ahead and check the steering column before calling the tow on this bastard. The column plastic enclosure is really loose and I occasionally try to close it tighter, although it's unlikely that affected any of the wirings inside.

[SteveJ]

While the MSD may not have needed the ballast resistor, unless someone move the Black/White wire over to the Green/White wire at the resistor, the resistor is still in the circuit. Also, reading 9.8 VDC at the coil is about where I would expect the voltage to be with the resistor in the circuit.

Anyway, I hope you or your mechanic can track down the short.

[EScanlon]

...Ok.. so I replaced the coil (with a non MSD brand if that matters), cleaned the plugs. Nothing.

...

edit: The new ign coil also gets overly hot to touch, can't rest your hand on it for more than a sec. I cleaned all the grounding wires.

This was your first clue that the wiring was off.

No wiring changes were made... since I didn't change anything else.

Sorry, but this is wrong. You changed the coil. Ideally ALL the wires would have been replaced EXACTLY as they came off, but then you wouldn't be having trouble.

All the wiring seems connected, nothing's been changed since last operation except for the coil itself. ...

Double check the wiring.

Somehow you're providing UNSWITCHED 12v+ directly to the coil. Unswitched power is not a normal part of the ignition circuit, so SOME re-wiring has occurred someplace. This is the reason your coilis getting hot with the ignition switch off, you're basically connecting a + source directly to a - ground AT the coil terminals. The negative post on the coil should be grounding THROUGH the distributor and not directly to ground.

FWIW

E

[Kennymonster]

Here are the updates for those who search similar problems in the future.

Got the Z back today, here's the culprit and final verdict.

Lack of spark issue: the MSD box was indeed shorted out, along with the voltage regulator on the alternator (280z type.) Apparently the current set up had an internal regulator inside the alternator AND an external regulator somewhere along the harness as well. One of them is now bypassed.

What a pain in the arse, it runs good now though.

[SteveJ]

To clarify - You had an internally regulated alternator, but you did not removed and jumper out the external regulator. That can cause overvoltage conditions, and it sounds like it may have burned out your MSD box.

Hence, E's statement was quite correct. You (or a previous owner) messed up the electrical system. By the way, I have done that myself in the past, but I fixed it after only blowing out a headlight.

However, unless the MSD also gets an unswitched 12VDC+ source, your solution doesn't address the previous problem of the coil having voltage with the ignition off.

Also, with the internally regulated alternator and electronic ignition, be on the lookout for feedback through the charging system keeping your car running after you shut off the key. The solution is to put a diode in the alternator circuit. If you search through Zhome.com, you can find the details.

[Kennymonster]

To clarify - You had an internally regulated alternator, but you did not removed and jumper out the external regulator. That can cause overvoltage conditions, and it sounds like it may have burned out your MSD box.

Hence, E's statement was quite correct. You (or a previous owner) messed up the electrical system. By the way, I have done that myself in the past, but I fixed it after only blowing out a headlight.

However, unless the MSD also gets an unswitched 12VDC+ source, your solution doesn't address the previous problem of the coil having voltage with the ignition off.

Also, with the internally regulated alternator and electronic ignition, be on the lookout for feedback through the charging system keeping your car running after you shut off the key. The solution is to put a diode in the alternator circuit. If you search through Zhome.com, you can find the details.

The Z has come to my possession that way, and I have not messed with any of the wiring despite that's what I keep hearing.

Fortunately my mech was competent enough to complete the diode method for me before I got there, and explained the possible consequences otherwise.

Only other thing we did was to completely replace the battery terminal harnesses, since they were rotted to hell. I did try re clamping with a better part of the cable during my troubleshoot, but they seem to be too far gone. Coil doesn't seem to be getting the regulated voltage any longer.

Thanks again for the past feedback guys.