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Author Topic:   Shock through spark plug wire

BBS posted 07-30-2008 12:13 PM ET (US)
I was troubleshooting a rough idling (seems like it miss fires at idle, but runs OK when rpms increase) and decided to press on my spark plug boots. I pushed on one and recieved a shock - is this normal or could this be my problem?
Landlocked posted 07-30-2008 01:54 PM ET (US)
Can't say if its normal but I've had it happen as well. I avoid touching them when the motor is running.
Jerry Townsend posted 07-30-2008 04:50 PM ET (US)
BBS - getting shocked by touching a spark plug wire is typical and normal - because, the spark voltage is high - somewhere north of 1,000 volts depending on the system. Of course, the current is low. But, touching a spark plug wire with the engine running - the spark only has to "jump" the thickness of the rubber boot - and if you are grounded, you will get shocked. Because the current is super low - it will not hurt you - just wake one up. ------- Jerry/Idaho
deepwater posted 07-30-2008 09:35 PM ET (US)
it might be time for new wires ,,how old are the ones you have now,,and i might add i have touched all my wires with the motor running and never received a shock,,if its getting out it could be shorting out
Bella con23 posted 07-30-2008 09:46 PM ET (US)
On some secondary wires, you can expose the metallic spark plug connector by pushing the boot onto the plug to far. I would like to think that all these plug wires are molded and the boot would not separate, but I have seen both type.
Joe
pglein posted 08-04-2008 07:09 PM ET (US)
In theory, it should not shock you through the boot. However, it is possible for the spark to jump out around the boot and shock you that way. If the wires or boots are cracked or brittle, they should be replaced. If you're having a problem with missing or inconsistent running, plug wires are often the problem.
contender posted 08-04-2008 08:14 PM ET (US)
I agree with pglein, it should not shock you, the wires/boots may have a crack, and as far as not hurting you...its a very small chance but if the shock is delivered at the correct time could put your heart in V-fib and you could die...good luck and don't touch the wires when the engine is running.
roloaddict posted 08-08-2008 12:49 AM ET (US)
It may be that your wires have a bit of that fine dust that is attracted to HV circuits. I have observed that this dust can provide a path past the insulating properties of the silicon wire/boots,plastics and ceramics in the system. This is basically a skin effect similar to how high frequency and above radio waves travel through conductors. You could be getting just a fraction of the sparks power but it still hurts.
As a kid, my cousin recieved a good beating after he cranked over my Road Runner while I was laying on the wet fender,in the pouring rain, reseating the coil wire in the 50KV Accel Racing coil. Seems he could not defend himself because he was laughing so hard. He still reminds me by sticking out his index and middle fingers and wiggling them up and down, duplicating the view he got of my legs from the drivers seat. After 25 years, you would think he would forget.
BBS posted 08-25-2008 10:43 AM ET (US)
Follow-up: Due to the age of the coils and wires on my 1987 Yamaha 115 I purchased and replaced all 4. The problem with the rough idle has gone away.

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Author	Topic: Shock through spark plug wire
BBS	posted 07-30-2008 12:13 PM ET (US) I was troubleshooting a rough idling (seems like it miss fires at idle, but runs OK when rpms increase) and decided to press on my spark plug boots. I pushed on one and recieved a shock - is this normal or could this be my problem?
Landlocked	posted 07-30-2008 01:54 PM ET (US) Can't say if its normal but I've had it happen as well. I avoid touching them when the motor is running.
Jerry Townsend	posted 07-30-2008 04:50 PM ET (US) BBS - getting shocked by touching a spark plug wire is typical and normal - because, the spark voltage is high - somewhere north of 1,000 volts depending on the system. Of course, the current is low. But, touching a spark plug wire with the engine running - the spark only has to "jump" the thickness of the rubber boot - and if you are grounded, you will get shocked. Because the current is super low - it will not hurt you - just wake one up. ------- Jerry/Idaho
deepwater	posted 07-30-2008 09:35 PM ET (US) it might be time for new wires ,,how old are the ones you have now,,and i might add i have touched all my wires with the motor running and never received a shock,,if its getting out it could be shorting out
Bella con23	posted 07-30-2008 09:46 PM ET (US) On some secondary wires, you can expose the metallic spark plug connector by pushing the boot onto the plug to far. I would like to think that all these plug wires are molded and the boot would not separate, but I have seen both type. Joe
pglein	posted 08-04-2008 07:09 PM ET (US) In theory, it should not shock you through the boot. However, it is possible for the spark to jump out around the boot and shock you that way. If the wires or boots are cracked or brittle, they should be replaced. If you're having a problem with missing or inconsistent running, plug wires are often the problem.
contender	posted 08-04-2008 08:14 PM ET (US) I agree with pglein, it should not shock you, the wires/boots may have a crack, and as far as not hurting you...its a very small chance but if the shock is delivered at the correct time could put your heart in V-fib and you could die...good luck and don't touch the wires when the engine is running.
roloaddict	posted 08-08-2008 12:49 AM ET (US) It may be that your wires have a bit of that fine dust that is attracted to HV circuits. I have observed that this dust can provide a path past the insulating properties of the silicon wire/boots,plastics and ceramics in the system. This is basically a skin effect similar to how high frequency and above radio waves travel through conductors. You could be getting just a fraction of the sparks power but it still hurts. As a kid, my cousin recieved a good beating after he cranked over my Road Runner while I was laying on the wet fender,in the pouring rain, reseating the coil wire in the 50KV Accel Racing coil. Seems he could not defend himself because he was laughing so hard. He still reminds me by sticking out his index and middle fingers and wiggling them up and down, duplicating the view he got of my legs from the drivers seat. After 25 years, you would think he would forget.
BBS	posted 08-25-2008 10:43 AM ET (US) Follow-up: Due to the age of the coils and wires on my 1987 Yamaha 115 I purchased and replaced all 4. The problem with the rough idle has gone away.