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CDI primary wiring through a firewall connector

Practical Motorsport Wiring - Professional Level

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Good morning brains trust,

I have recently completed a project that runs a CDI ignition system, KV12 ECU & P14 PDM running an FJ20. All engine wiring is passing through a firewall connector, on advice from a reputable motorsport wiring guru in Aus. I have wired the primary coil wires through the firewall connector. Now the car is seeing some issues on the dyno with signals from the optical sensor in the factory distributor. However a cherry sensor on the crank is not seeing these issues.

M&W basically said don't do this, maybe im a sucker for punishment but im sure i am not the first person to do this.

Any insight into the potential noise interference or maybe a dodge sensor ?

Thanks Gents


This is a really tricky one, but if you can scope the signal line you're seeing noise on, and the noise occurs at a frequency related to the firing of the CDI, then that is indeed the likely culprit. CDI wires are pretty high-energy, so can absolutely introduce noise. I;ve not struck it myself, but could certainly see it happening.

Nissan optical sensors aren't the greatest in general. Not sure how the FJ one looks but SR20 optic discs have way too many slots in them for accurate engine position at higher rpms. You could try swapping out the disk to a lower slot count, a few companies make these.

Is the sensor wired with shielded cable?

@Andrew, he is only using the optical for sync, I suspect a single slot.

@Angus, Im not sure about the FJ20 distributor specifically, but be aware in many of the other Nissan optical CAS's, the ground pin is internally connected to the CAS body - thereby possibly coupling your sensor ground to the engine block (check with a multimeter). So with high powered ignition systems passing high voltage through the engine block you may have a path for that to get on to sensor ground.

If it is a missing tooth crank you should be able to unplug the distributor once its running to confirm if it is only the optical that is causing your issue.

Ah ok that may be it, ill go and have a look at the sensor in detail, hopefully that will assist with the noise issues.

ill report back on findings, hopefully round 2 on the dyno is a bit better for this little car :)

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