P38A missfire

scottdej · Dec 2, 2015

hi guys, looking under the bonnet at night i can see the spark plugs arcing around their body, i changed the plugs, but still the same, engine is new and run on lpg with magnecor leads, does anybody have any idea what the cause of this is and the remedy.
thanx in advance.scott.

jamesmartin · Dec 2, 2015

change the leads

scottdej · Dec 2, 2015

yeah thats crossed my mind, but at £80 thats an expensive way of elimination, especially if it doesnt work, also id have thought it unlikly to be the leads as i can see arcing on all 8

scottdej · Dec 2, 2015

anyone else?

biketeacherdave · Dec 2, 2015

jamesmartin said:
change the leads

+1

jamesmartin · Dec 2, 2015

scottdej said:
yeah thats crossed my mind, but at £80 thats an expensive way of elimination, especially if it doesnt work, also id have thought it unlikly to be the leads as i can see arcing on all 8

its either them or youve got a massive plug gap

scottdej · Dec 2, 2015

plug gap is 0,7mm as recommened for lpg

TVRConvert · Dec 2, 2015

biketeacherdave said:
+1

+2

Henrik97 · Dec 3, 2015

Magnecor make different types of leads. Some are made with internal RF suppression (to be used with regular plugs) and others are "straight through", meant for use with suppressed plugs. If you use suppressed plugs with suppressed leads, The resistance from coil to ground will be excessive and you may get arcing elsewhere as well as a poor spark. Check that your plugs and leads are the right combination. I agree with you that replacing the full lead set is probably premature - magnecor leads should last a very long time and it's highly unlikely for all of them to go bad at once.

Henrik

domino · Dec 3, 2015

Unless it's a bad batch.

wammers · Dec 4, 2015

Henrik97 said:
Magnecor make different types of leads. Some are made with internal RF suppression (to be used with regular plugs) and others are "straight through", meant for use with suppressed plugs. If you use suppressed plugs with suppressed leads, The resistance from coil to ground will be excessive and you may get arcing elsewhere as well as a poor spark. Check that your plugs and leads are the right combination. I agree with you that replacing the full lead set is probably premature - magnecor leads should last a very long time and it's highly unlikely for all of them to go bad at once.

Henrik

All carbon cored leads have built in RF suppression. Most modern automotive plugs will also have built in resistance.

TVRConvert · Dec 4, 2015

To be honest, a lot of my mates (TVR) don't rate the Magnecor leads, A standard set of leads (don't buy anything with Intermotor on though) will do the trick

Henrik97 · Dec 4, 2015

wammers said:
All carbon cored leads have built in RF suppression. Most modern automotive plugs will also have built in resistance.

True, true. But non-suppressed plugs are still available. For NGK, a BP6ES is not suppressed, whereas the otherwise identical BPR6ES is. I had to change plug type on my old Alfa for this very reason (switched from copper core to Magnecor leads). I didn't know that all carbon-core leads are suppressed, but you're probably right. In that case I would strongly suggest that the OP tries non-suppressed plugs before he buys another set of leads.

Henrik

biketeacherdave · Dec 4, 2015

when i finnally get round to fitting my lpg convertion im going to fit a new standard set of leads n plugs as research suggests the magnacor leads are no better

wammers · Dec 4, 2015

Henrik97 said:
True, true. But non-suppressed plugs are still available. For NGK, a BP6ES is not suppressed, whereas the otherwise identical BPR6ES is. I had to change plug type on my old Alfa for this very reason (switched from copper core to Magnecor leads). I didn't know that all carbon-core leads are suppressed, but you're probably right. In that case I would strongly suggest that the OP tries non-suppressed plugs before he buys another set of leads.

Henrik

Try using carbon cored leads on an old points and coil system if you really want to struggle for a decent spark. Modern systems produce much higher voltages to compensate for high resistance suppressed leads and plugs. Have a 50 metre reel of stainless shielded, wire cored ignition cable in garage somewhere. Used it on the aircraft i built as ignition lead shield grounded to stop RF. This stuff non shielded was used on Canberra bombers as igniter lead.

Koen · Dec 4, 2015

change the leads

i assume you have checked them? Do they still look clean and do they feel solid on the connections?

sparky, sparky is not good, unless it's inside the camber

wil2813 · Dec 5, 2015

biketeacherdave said:
when i finnally get round to fitting my lpg convertion im going to fit a new standard set of leads n plugs as research suggests the magnacor leads are no better

right choice imo

P38A missfire

scottdej

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jamesmartin

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scottdej

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scottdej

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biketeacherdave

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jamesmartin

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scottdej

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TVRConvert

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Henrik97

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domino

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wammers

No longer with us, RIP

TVRConvert

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Henrik97

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biketeacherdave

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wammers

No longer with us, RIP

Koen

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wil2813

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