Thread: Possible problem with ignition coil wiring??

Originally Posted by The Bullfrog

Hi all, Hoping someone can help.

My supercharged disco has been having some issues of misfiring. As it is supercharged it is running a Haltech ECU and i have had all that side of it checked on a dyno. (Unfortunately the misfire had disappeared by the time I drove to Perth).

My question is about the coil and associated wiring which is still standard coil but with different amp.

There is a capacitor/suppressor coming from the +ve post and mounted to the coil mount.

My belief is that this is just to suppress radio interference??? and the guy who did the supercharger conversion (used to work at JRT) agreed. However, when the suppressor is disconnected the car stalls and won't start till it is connected again with a sound earth.

Talking to him on the phone, he couldn't work it out and said that shouldn't happen.

Can someone confirm this shouldn't occur and what the possible causes could be. (i have sourced some wiring diagrams, so will be using that to confirm it is wired in correctly, even though it appears to be!!)

Thanks

The Haltech computer may be picking up stray electrical noise from the coil circuit. It should have an input from your dissy/crank angle sensor (and what engine are we talking about?) and is being corrupted by random pulses. Try moving the Haltech wires away from the main loom, or identify the pickup wires and shield them with coax cable.

which engine would be some great info i suppose, 3.9 v8 and vehicle was built june 94. has the bosch coil.

not sure how these random pulses would cause engine to stall when i disconnect the suppressor from the coil though??

Originally Posted by The Bullfrog

which engine would be some great info i suppose, 3.9 v8 and vehicle was built june 94. has the bosch coil.

not sure how these random pulses would cause engine to stall when i disconnect the suppressor from the coil though??

The pulses generated by the pickup coil in the dissy are very small, perhaps they are being swamped by electrical noise so they aren't being read by the ECU? A similar effect has been reported during replacement of Lucas amps when the pickup wire are unshielded and run close to the alternator.

Hey, it's only a theory, if you get a better one run with it.

Ok, Now see where you are going, without the radio suppressor connected the interference from the alternator is too great..... Is worth a shot, will try to re-route the wiring as i think it does go past the alternator... or would putting it in rubber vacuum hose or similar shield it enough?? Or do both?

Cheers

Originally Posted by The Bullfrog

Ok, Now see where you are going, without the radio suppressor connected the interference from the alternator is too great..... Is worth a shot, will try to re-route the wiring as i think it does go past the alternator... or would putting it in rubber vacuum hose or similar shield it enough?? Or do both?

Cheers

Rubber hose isn't shielding, its insulation, different concept altogether. Insulation is for stopping electric leakage (eg sparks) and woven metal braid is for stopping magnetic fields.

Basic 101 EMF training: passing a current through a wire generates a magnetic field around a wire. If you vary the current (eg AC current) the magnetic field will vary and any other wire placed within the changing magnetic field will feel an induced current. This is the basis for all transformers generators and electric motors. So a suggested way of shielding a cable is to wrap metal foil or fine mesh around it, then tape or binding to hold it together, then securely earth one end of the shield.

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