92 XJ40, 148,000 miles. I posted this question in XJ 40 forum as well.
What could cause sparking from center (discharge to dist) wire to terminal posts?. Wire is new, two coils tried, same thing. Coils not cracked, insulating boots are in place and look fine. Car will idle but shaky on acceleration, shorting gets worse. Battery and intake grounds clean and tight. Ideas??

 

There was a TSB WAAAYYY back in the early 90s about the king lead and coil tower HT tracking. There was a coil tower boot cover issued to prevent this.

Here is and old TSB

I don't have the earlier one in .pdf, only in paper.

The 'fix' was to turn the wire terminals away from the tower and install the boot with dielectric grease.

bob gauff

 

As long as you are sure the coil tower is not cracked, you've tried two so I'll assume at least one is good, the other cause is excessive secondary resistance. This excessive resistance causes the spark firing voltage requirement to get too high; that means the easiest path to ground is the coil terminal instead of the plug. You need to make sure the plugs are the correct ones and the gap is set correctly. Also get good quality plug wires installed [especially the coil wire] and check/replace the cap and rotor. About the only other thing that can contribute to this is the coil primary wires being reversed. Original equipment coils have primary terminals of different sizes to help prevent this from happening, but some folks still get them backwards.

Hope this helps!

 

If the HT leads to distributor and from distributor to sparkplugs are old, they will have gone high-resistance. They are usually "supressor leads", meaning what would be a wire conductor inside the insulating lead is in fact a very long resistor, looking exactly like graphited string. Also if these leads have 'had it' you will have misfiring problems. AND much worse in damp weather.
A once and for all fix is to replace the leads with WIRE high-tension leads, and install a 10K0 (10,000ohm) separate supressor in the lead from the coil to distributor. This new supressor simply screws into the lead. You will then never have that particular problem again. As a bonus, you will have a better fuel consumption too, by reliable sparking.
FYI, the sparkplugs loading will hold down the high-voltage spark from the coil to around 30Kv. or so, but if the HT leads have gone almost infinite resistance, this voltage can go to 50 or 60Kv, and that's due to modern "ignition amplifiers" as they now call them. (We called them "transistorized" back in the 1970s as they replaced simple contact breaker points + a capacitor -- good old days eh?). So it's not surprizing that such a high voltage flashes over the coil insulation down to the nearest ground. You should also check the inside of the distributor for any signs of flashover -- it leaves a very slight carbonized trail behind it. If you find one, a replacement is indicated.
Leedsman.

 

Thanks to all once again. I just replaced cap and rotor prior to noticing arcing, don't know if it was doing it before or not. Checked resistance of all 6 plug wires, all checked ok with ohm meter and consistent (as lengths got shorter slightly less resistance)
Plugs were brand new from PO, but R9YC not R12YCC. I did notice slight "wiggle" with Dist cap installed, but only one cap spec'd as far as I can tell for that year.
Still have a couple codes to clear (EGR sensor and Throttle potentiometer) will go with high pro wire set once done just to eliminate potential problem. Existing set is the carbon rope type of unknown vintage. Any recommendation on supplier?





















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