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shorting spark plug leads 6G72 engine


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Hi, new on here. Anyone know about short circuit coilpacks and consequent missfire? I have replaced 3 so far and all show signs of electrical burn through on the rubber tube going down to the spark plug. OK I am using second hand replacements as new ones are so expensive. I can use just the tube but these are difficult to find.

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Are you using the specified spark plugs, and/or are the plugs gapped correctly?

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yes, using plugs as detailed in handbook. Problem arose before fitting new plugs and seems to occur on the plastic tube that goes from the coil to the plug top. It shorts between the tube and the head. The tube is about 10cms long.

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OK, so if the plugs are good, the most likely possibilities are either that the plug leads and suppressors are just old, or that the leads and suppressors are not OEM grade. 

Plug leads and suppressors do break down after a few years due to the constant heat they are exposed to, but replacing them with old, used leads that are likely just as old won't fix the problem. Best thing to do here is to replace the leads and suppressors with OEM parts.

Edited by treks
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Over time the insulating material develops small cracks and weaknesses that are not visible to the naked eye. So, considering that electricity is much like water in that it will always follow the path of least resistance, it becomes easy to see how several tens of thousands of volts will jump through a break in the insulation to the point that is closest to a grounding point- which in this case, is the point on the cylinder head that is closest to a weak spot in the insulating material.

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Is your coilpacks are working fine...? Is your HT leads connecting in proper order on each bank? Is this shorting happening on all tubes or just one or two?

I assume 6G72 means 3.0 Pajero, do you mind sharing some background history as to how and when you spotted this?

Let's root for each other & watch each other grow.

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To some extent, I agree with treks as Mitsubishi coil and spark related department is extremely sensitive. I vaguely remember long ago something happen with my 6G74 and tried coil pack from scrap and it did't work out as expected. Eventually I have to buy 3 new coil pack as Mitsu support 2 HT lead per coil, so you don't need six.

Let's root for each other & watch each other grow.

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the 6G72 is fitted to quite a number of cars in USA and Japan. We buy mostly used imports from Japan (I am in New Zealand). My car is a 99 Chariot Grandis Royal 7 seater. The fault showed up as a miss fire with usual hesitant running. It would be easy to mistake it for unbalanced wheels or bad plugs. I was not looking forward to removing the rear plugs as when I looked online it seemed to be an involved process. Luckily on the Grandis there is a bit of space at the back of the engine. You need a long plug socket to reach down in the head and you don't want to get it stuck down the hole! As I had a set of plugs (NGK) I set about changing them. It was then I noticed the burn through on the tube. It was easy to not notice this fault as the burn through mark was only small. I have replaced 3 so far so am getting good at it!

coil.jpg

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