Ignition Lead Problems

[MKnight702]

I have had some rough running issues with the XI, eventually tracked it down to presumably dodgy ignition leads but symptoms were strange. When the plug lead was attached the cylinder didn't fire, when the plug lead was detached but held close to the plug it would spark accross and fire.

Replaced the plug leads and plugs last Thursday and the car ran fine. Last night I developed the misfire again. I will pull the new leads (Bosch) tonight and take them back to Halfords to see if it was just a duff set, but is there anything that anyone else can think of that would cause this sort of issue?

The car is running Megajolt wasted spark with a Ford coil pack not the old clockwork stuff.

[GLLHG]

Bit of a rough guess, but if the spark is being delivered OK to the end of the lead ( which it seems to be from what you say) could it be something in the plug itself?
Sorry I know that you've probably tried another plug on that lead/cylinder and checked that the ECU/ coil pack side of thiongs is OK

[Steve_D]

If it sparks when 'air gapped' then the lead is fine but the plug is duff/wrong gap/fouled/etc.

Steve

[MKnight702]

Steve_D said:

If it sparks when 'air gapped' then the lead is fine but the plug is duff/wrong gap/fouled/etc.

Steve

But why would a fouled plug spark when all I did was remove the lead and hold it close to the plug? The plug was exactly the same as before, still in the engine.

BTW I also replaced all 4 plugs with new ones and a week (200 miles) later the same problem, would a plug foul that quickly?

[Steve_D]

A plug can foul in minutes if the right conditions exist.

Someone may be along to explain exactly what is happening electrically but all I know is that removing the plug lead and making the spark jump even further somehow causes the spark to have more power and in doing so can break down what ever is fouling the plug hence the cylinder firing again when air gapped.

If the base problem still exists then the plugs will foul again.
Are the plugs the right type for the engine? Plugs of the wrong type or temperature rating will foul.
Are the removed plugs oily or soot covered?

Steve

[chard]

Try observing in the dark to see if you have any loose electrickery.

I had this, traced to a tiny crack in the head spraying water onto one of the leads under load. The spray was so fine it evaporated straight away and hardly caused any coolant loss. Spotted the problem at night after weeks of trying to sort it. Even proffesionals were stumped.

[Mr2Mike]

MKnight702 said:

Steve_D said:

If it sparks when 'air gapped' then the lead is fine but the plug is duff/wrong gap/fouled/etc.

Steve

But why would a fouled plug spark when all I did was remove the lead and hold it close to the plug? The plug was exactly the same as before, still in the engine.

This was the standard way of getting knackered two stroke bikes with fouled plugs to run years ago. A fouled plug allows the HT to to leak directly to ground, and never build up enough voltage to ionise the air in the spark gap. By pulling the spark plug lead away from the plug slightly to form an external spark gap, no current flows through the plug until the HT voltage has risen high enough to to cross the external spark gap, at which point there is often a high enough voltage to form a weak spark on the fouled plug.

I new set of correctly gapped plugs would certainly be my first starting point.

[bertelli_1]

Is this a Mitsubishi Evo (XI doesn't tell me a lot)? Whatever the car it probably has a capacitor on the coil circuit (small cylinder shape), which can cause a weak spark - you symptoms suggest this type of failure. On the Mitsubishi it is attatched to the rocker cover / inlet manifold.

I'll take my £40 diagnostic fee now please.

ETA - just re read & saw you are running MS, the ford coilpack should have the capacitor fitted, if fitted you could try removing it & see if that cures the fault.

Edited by bertelli_1 on Saturday 26th June 13:10

[dan19evans]

bertelli_1 said:

Is this a Mitsubishi Evo (XI doesn't tell me a lot)? Whatever the car it probably has a capacitor on the coil circuit (small cylinder shape), which can cause a weak spark - you symptoms suggest this type of failure. On the Mitsubishi it is attatched to the rocker cover / inlet manifold.

I'll take my £40 diagnostic fee now please.

ETA - just re read & saw you are running MS, the ford coilpack should have the capacitor fitted, if fitted you could try removing it & see if that cures the fault.

Edited by bertelli_1 on Saturday 26th June 13:10

its a westfield XI.. try looking in his profile

[MKnight702]

I have checked the plugs, given them a good clean but no dice (they are the correct ones). I have now ordered a new coil pack to see if that gives me any joy.

[Mr2Mike]

bertelli_1 said:

ETA - just re read & saw you are running MS, the ford coilpack should have the capacitor fitted, if fitted you could try removing it & see if that cures the fault.

The capacitor is for RF suppression, it would have little effect on the spark.

[MKnight702]

Well, tried a new coil pack and no change. Think the head will have to come off next, I may just try new plugs first for a look see but don't hold much hope.

[Steve_D]

MKnight702 said:

......... Think the head will have to come off next........

What do you think that will tell you?

Steve