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rheng

No Spark with MSD

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The car in question is a 1971 240z with a 280z engine and 280zx distributor.

I'm currently having some issues getting spark from my 6A MSD. At one point, the car did run fine with this exact setup and wiring shown in the attachment to this post (and here: https://www.classiczcars.com/uploads/monthly_2016_10/1918msd_zx_240z_1r2.jpg.9235e4af03e7d71e6584ff639ad81311.jpg) . However, the car currently isn't starting with this configuration. I was having some stuttering issues in the past, and the last two times I took the car out, it died and had to get towed home.

The car seems to run fine if I bypass MSD entirely and wire the ignition module and tach directly to the coil. With the MSD, I do not get spark from the coil. I have a brand new cap, rotor, ignition module, and wires installed.
Here's where I am currently at with my troubleshooting:

  • I am able to get spark from the coil wire when doing the green/purple and white wire test indicated in the MSD manual (see below). I think this suggests that the MSD is wired correctly and is capable of firing.
  • New MSD. Did not work. I replaced with a 6AL and did not get a flashing LED when cranking. So, it doesn't look like the ignition module signal is not properly interpreted by the MSD (not sure if this is a possibility?). This also came with a new wiring harness, so I'm thinking all the wiring should be good.
  • Replaced ignition module. Didn't seem to help.
  • Bypassing the MSD. Car starts and runs just fine.
  • Bypassing the tach adapter. Still no spark.
  • Directly wiring the B/W wire from MSD to the battery to eliminate the possibility of the ignition switch causing any issues. No spark. Its also worth noting that I have confirmed that, when the MSD is wired as shown in the diagram (ie not directly wired to the battery as previously mentioned), this connection sees 12V when switched on and around 9.6v - 9.8v when cranking.

Running out of ideas here, so I'm hoping someone here can help me out!


MSD Manual test procedure: https://www.jegs.com/InstallationInstructions/100/121/121-6425.pdf

1918msd_zx_240z_1r2.jpg.9235e4af03e7d71e6584ff639ad81311[1].jpg

Edited by rheng

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On 9/13/2020 at 9:43 AM, rheng said:

280zx distributor.

The car seems to run fine if I bypass MSD entirely and wire the ignition module and tach directly to the coil.

I am able to get spark from the coil wire when doing the green/purple and white wire test indicated in the MSD manual (see below). I think this suggests that the MSD is wired correctly and is capable of firing.

New MSD. Did not work. I replaced with a 6AL and did not get a flashing LED when cranking. So, it doesn't look like the MSD is picking up any signal from the ignition module. This also came with a new wiring harness, so I'm thinking all the wiring should be good.

Bypassing the MSD. Car starts and runs just fine.

 

Some of your troubleshooting doesn't make sense.  If there's no signal from the ZX distributor then how can it run with just the ZX distributor?

Coils can overheat.  The fact that it runs with just the 280ZX distributor shows that the problem is caused by the MSD unit.

I'd take it out and drive it using just the 280ZX distributor.  At high RPM the coil should see the same load that it does with the MSD.  MSD only does multi-spark at lower RPM.  Run at high RPM and see if the problem happens again.

 

Edited by Zed Head

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14 minutes ago, Zed Head said:

Some of your troubleshooting doesn't make sense.  If there's no signal from the ZX distributor then how can it run with just the ZX distributor?

Coils can overheat.  The fact that it runs with just the 280ZX distributor shows that the problem is caused by the MSD unit.

I'd take it out and drive it using just the 280ZX distributor.  At high RPM the coil should see the same load that it does with the MSD.  MSD only does multi-spark at lower RPM.  Run at high RPM and see if the problem happens again.

 

Sorry, what I meant to communicate in my original post is that the ignition module from the ZX distributor, is sending a signal (i.e. there is indeed a signal from the distributor as indicated by the ability to run without the MSD). But, for whatever reason, the MSD is not firing when the signal is received. That said, I have also tried a brand new 6AL MSD which did not solve the issue. 

I haven't tried to drive the car without the MSD (mostly afraid of being stranded again!). However, I did let it idle for a good 20ish minutes and occasionally revving it a few times in my garage. It seemed fine, but I do agree it would be a good spot check to actually drive the car without the MSD under actual load. 

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There's always the "check your grounds" advice.  Grounds might be the most overlooked problem in electrical troubleshooting.  Some ignition modules ground through the mounting points.  

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you do not need the zx module with a msd 6al unit that just creates 2 different signals . wire the zx dissy  direct from the 6al unit from the ford plug that comes with  the msd to the 2 wires inside the dissy . I am not home,but look up the correct way to splice the color wire in order. I made a small metal plate to blank off the hole on the side of the zx dissy when I removed the nissan module. I could never get my tach working with the tach adaptor. I tried resistors and adaptors also . my z is a early 74 260 car and I mounted a small tack  in the car. maybe one day I will looked into that  again.  

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