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Talk to me about HT leads please - I dont understand

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4 replies to this topic

#1 sgking


    ST200 Limited Ghia X

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Posted 18 March 2017 - 11:39 AM

Hi all.


Re HT leads.


I have just fitted new ones to the car, but it is now misfiring worse than before? It was just a little blip when put foot down in 5th but now its much more lumpy? (brand is prospark, by the way)


I have checked at night in dark and I can see arcing going through the leads in the new ones too - I thought this was an indication of old ones going bad? I thought that new ones would have no arcing visible at all.





Mondeo 2000 ST24

Mondeo ST200 Limited Edition no 181/300 'Ghia X'

#2 Paul RS

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Posted 18 March 2017 - 12:38 PM

Where do you see arcing?

#3 raynkar


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Posted 18 March 2017 - 12:43 PM

Are you sure the HT leads were the issue in the first place?
The Ford 'double spark' coul packs are known to crack and have issues.

What are the plug electrodes like?

Edited by raynkar, 18 March 2017 - 12:44 PM.

#4 mike4369


    Big Megger

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Posted 18 March 2017 - 02:11 PM

Rare to see arcing from a lead - more likely a lead will go open circuit, especially the compressed carbon conductor types. Since there are very high voltages being generated it only takes a hairline crack in the coil pack to cause arcing, and gets worse as the plastic is burnt to a carbon like state. Take the coil pack off and check it visually for any signs of burning.

What are the plug electrodes like?

I agree  to also check the plugs and change if needed.

Some info here which may be of interest


Edited by mike4369, 18 March 2017 - 02:14 PM.

#5 Woody123



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Posted 21 March 2017 - 03:01 PM

New leads can finish off old spark plugs and vice versa, try changing the spark plugs to NGKs and see if there's any improvement

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