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Discussion Starter · #1 ·
Have a '79 with 351M that suddenly lost some power, has a serious case of the shakes at low RPM and doesn't want to idle too bad. Would like to pull off plug wires from the dist. cap to try to pinpoint a potential dead cylinder. While being effective test method, this also seems like a great way to get shocked repeatedly. Is there any way to do this without getting shocked? Would gloves be enough to insulate me? If I recall the voltage is pretty high there. Tips or tricks would be appreciated. (I don't have compression tester or I would just do that).

Also, this is just a guess on my part about the dead cylinder at this point, any other common things to check would also be appreciated.
 

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Dead Horse
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ive done it before, and never got shocked

bare hands btw
 

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Satyr of the Midwest
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They do make special spark plug wires with a metal strap or ring on the outside just for this purpose. When you want to kill a cylinder, you just attach a grounded wire to this metal piece, and voila.

I've never been too big of a fan of disconnecting spark plug wires, simply because all of that energy has nowhere to go, and bad spark plug wires are a contributor to killing ignition control modules. But if you have to do it, I'd think it'd be a lot easier to disconnect at the distributor cap instead of the spark plug. Keep in mind that you'll only get a good poke if you're completing the circuit, which means you should NOT be touching any part of the vehicle's body while your hand is on the spark plug wire. I've been kicked pretty hard while resting one hand on the distributor cap and the other on the fender on my Mustang equipped with an MSD 6BTM box; one of the wires' boots had a good cut in it. Not enough to kill me, but definitely enough to make me go AAAAARGH!!! :D
 

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Southeast Utah Native
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If all you want to do is verify that each wire has spark use an inductive timing light. If the light doesn't flash there is no spark on that cylinder. Simple, effective, and safe.
 

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crank trigger
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Rick3373 said:
If all you want to do is verify that each wire has spark use an inductive timing light. If the light doesn't flash there is no spark on that cylinder. Simple, effective, and safe.
:stupid

or you ghetto it by using an sparkplug. pull the wire, put the plug in, hold it next to ground and have buddy crank the ignition. if you are worried about a cylindar not having compression, i would pull the plugs and look for a fouled one.
 

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Discussion Starter · #8 ·
Thanks for the responses. I'm pretty sure it's one cylinder down, I'm not sure if the issue is electrical or mechanical at this point. The major issue is that I'm time limited on troubleshooting this. Going by the whole "work smarter, not harder" theory, I was hoping to isolate the cylinder, then check electrical/mechanical on that one rather than pulling all plugs and having to deal with seized stuff that might not even be the main problem (a problem yes, but a correctly firing cylinder with a plug that is seized is not my main concern right now, I'll deal with that later).
 

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Rick3373 said:
If all you want to do is verify that each wire has spark use an inductive timing light. If the light doesn't flash there is no spark on that cylinder. Simple, effective, and safe.
He's got my vote!!!
 

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i'd say go ahead and pull 1 plug at a time see if it is fouled and if it sparks, since your that far just put you thumb over the spark plug hole and crank it over from the solinoid with the key off to check for compression on all cylinders
 
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