Coil problem?

Why not jut fit a new coil and be done with it?

It sounds like a cylinder isn't firing every time, especially at tickover. I would recommend a compression test.

Steve

Riiiiight.

Re-read my post, especially the bit where I mentioned that I had already tried replacing the coil.

Done that? good.

Any other helpful comments? ;-)

Will

The more likely cause is arcing over from the HT lead(s) rather than coil.

Ooops. Sorry about that - it's been a long week so far! :-)

Robert

Best way to spot this si to run the engine at night with the bonnet open - the place where the arcing is happening is usually self-evident in the dark.

Yes it's not like they are repairable (not with any degree of reliability)

I've tried this and have noticed that the HT lead appears to want to arc to *anything* - touching it makes small arcs to my fingers. Both non-HT connections to the coil occasionally show a small blue spark, too - though it's not clear if the arcs are from the HT lead as the sparks are too small / faint though I suppose where else *could* the arcs be from?

Is it normal for the middle of an insulated HT lead to arc to ground? I've tried putting insulating tape around the terminals on top of the coil but the fact the HT lead is arcing makes me thing something else is amiss.

Heyelp!

Will

The insulation of your HT leads has broken down. I would just replace them all as a set, and while you are there you might as well change the dizzy cap and rotor arm (unless you know they are recent and in good condition.) Should sort your problem, and won't cost too much. A misfire, on the other hand, will do horrible things to your cat and they are more expensive. BTW - what state are your plugs in? Worn or wrongly gapped plugs will put more stress on the HT circuit.

Just noticed an earlier thread about HT leads getting dirty/wet and old HT insulation perishing so thought I'd mention that the leads were replaced about 1 or 2 months ago and that I've tried wiping it down with tissue (although maybe not very thorougly)

Will

Sounds lika dodgy(cheap?) HT lead. Or a very wet/contaminated one.

I had new plugs and HT leads fitted within the last 2 months.

..although, now I come to think of it, the AA guy who looked at my car recently did say that the leads were 'wrong' but I have no idea in what way - I assume they're not the right type but don't know enough about them to be able to tell.

The leads are marked as :

"Hotwires silicon high performance 0879D 15K-ohm"

Are these leads suitable or did the garage screw up?

Will

I can't see why the leads should be wrong - If I remember right, aren't Hotwires the 'one lead fits all' type, with a multi fitting end which fits most plugs/ coils/ dizzy caps and adapters for the rest. Can't see why there should be a problem, unless you have the wrong adapters (if needed) or they aren't connected correctly. Have a check - if these are the ones I'm thinking of, you have to make sure the metal bit is a good fit before the rubber boot goes on, and you're supposed to expand or squash the metal bit as needed. It may be that the connector is rattling about loose and the boot is holding it all together.

Yea, checked that - both ends of the HT lead fit snugly..

From the sounds of it and reading through the earlier post about HT leads, it sounds like the lead itself is knackered as it should be arcing from the middle..

Will

Just one more thought - it's just the lead from coil to distributor that's arcing? If so I'd double check both the dizzy cap and rotor arm, as it's not unknown for them to fail. I am just surprised that the lead would fail so quickly, and if there is a break in the circuit it's just possible that the HT is finding it easier to track along the lead than jump the gap - if the carbon brush is stuck/broken, or the contacts are badly pitted (hope I'm making some sense here!)

HT will take the easiest path to ground. This *should* be the plugs in normal circumstances. If it's jumping from the coil lead, I'd guess at a problem with the dizzy cap or rotor arm.

I swear by Holt's Damp Start. If you don't want to mess around trying to dry things out completely (as you evidently are not doing) spray this on the electrical system. Brilliant!!

Rob Graham

Yes, I've seen a case where the carbon brush got displaced when the dizzy-cap was being refitted - the engine still started and idled, but misfired like an epileptic toad when the throttle was opened [higher spark-voltage needed to fire the engine under load].

Also it sounds like you've got non-original plug leads: I've seen several problems with these [particularly on Ford Zetec engines in Mondeos, and on mid-1980s Vauxhalls] - can you get your hands on a set of genuine plug leads and see if that fixes it?