james h
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| posted on 10/4/15 at 02:04 AM |
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Odd spark plug issue
I've had terrible running since one of my two coils fell onto the exhaust manifold (snapped ali bracket, not made by me and now replaced with a
better designed, thicker carbon fibre piece).
Driving back after this happened, it felt and sounded like it was running on fewer than 4 cylinders. So it was clearly the coil, right? Ordered a s/h
one off eBay. But oddly, the cylinders 1 & 4, run by the non melted coil are the only ones not firing. I assumed wrongly!
Checking the gaps on the plugs, 1 & 4 are way out! Far too large. One a little more than the other. 2 & 3 are fine.Any clues as to why this
would happen, and why at the same time as the other coil got a bit melted? They have been on the car for about 3-4K miles.
I'm going to buy some iridium ones tomorrow, hopefully that will cure the issue, but it all seems a bit weird to me.
James
[Edited on 10/4/15 by james h]
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britishtrident
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| posted on 10/4/15 at 08:43 AM |
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The polarity of the spark has an effect on the rate of plug electrode erosion, on a double ended coil pack one plug gets a negative ht voltage the
other a positive ht.
Excessive spark plug gap is one of the main causes of coil pack failure, an over wide plug gap generates excessive ht voltage before the spark can
jump the gap and often results in a breakdown of the insulation of the coil pack.
From experience on the Rover K16 eu 3 engines I found when coil pack fails it pays to replace both coil packs & the plugs and leads.
For emission reasons many manufacturers specify spark plug gaps that are on the wide side, I find setting the gaps to about 10 to 15 percent lower
than OEM setting as this helps increase the life of both coil pack and the plugs.
[Edited on 10/4/15 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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james h
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| posted on 10/4/15 at 08:52 PM |
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quote:
Originally posted by britishtrident
The polarity of the spark has an effect on the rate of plug electrode erosion, on a double ended coil pack one plug gets a negative ht voltage the
other a positive ht.
Excessive spark plug gap is one of the main causes of coil pack failure, an over wide plug gap generates excessive ht voltage before the spark can
jump the gap and often results in a breakdown of the insulation of the coil pack.
From experience on the Rover K16 eu 3 engines I found when coil pack fails it pays to replace both coil packs & the plugs and leads.
For emission reasons many manufacturers specify spark plug gaps that are on the wide side, I find setting the gaps to about 10 to 15 percent lower
than OEM setting as this helps increase the life of both coil pack and the plugs.
[Edited on 10/4/15 by britishtrident]
Thanks for your help. I didn't know about that mode of failure before your post!
Unfortunately I still have the problem.
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