Safe to unhook plug wires while running?

[75-JOHNSON]

Im just wondering if i will get a bad shock if i try to disconect the spark plug wires on a running 75 johnson to check if its firing? previous bad experience with snowmobiles and motor bikes makes me weery

 

[buddybarnhill]

Re: Safe to unhook plug wires while running?

you shouldnt if you hold it towards back of plug itself

 

[Rick.]

Re: Safe to unhook plug wires while running?

Safe? Probably won't kill you, unless you have a heart condition. I have never been able to do it without getting zapped, but some times you just need to do it anyway. Try some good quality rubber gloves and I think you should be fine. If anyone has a fool proof method I'd like to hear it. Rick.

 

[F_R]

Re: Safe to unhook plug wires while running?

Safe? Probably won't kill you, unless you have a heart condition. I have never been able to do it without getting zapped, but some times you just need to do it anyway. Try some good quality rubber gloves and I think you should be fine. If anyone has a fool proof method I'd like to hear it. Rick.

There are such things as insulated gloves and special pliers for such things. But no way in heck are you going to see me grab and disconnect a spark plug wire bare handed. Especally on that motor. That thing can throw a one inch long spark with ease.

As an aside, the Florida Power and Light guy came out to do some service work on our underground power lines. I watched as he removed the lid from a hole in the ground, reach in and pull the wires out and do what he had to do (the power was on). His only protection was some big yellow gloves. He was on his knees on the wet ground and the hole was full of water!!!!!! I'd rather face a roaring lion than do that. I HATE getting shocked.

Oh yeah, back on topic---the fool proof way is to disconnect the wire and ground it or attach a spark checker BEFORE starting the engine. It is a severe strain on the ignition system to just remove the wires without giving the spark someplace to go. Or if you must disable the plug while it actually is running, make up a temporary exposed jumper plug wire so you can short it out with a screwdriver to ground.

 

[Les Robb]

Re: Safe to unhook plug wires while running?

Agree with FR, bare handed your gonna get zapped. Years ago they made a set of bright yellow insulated plastic pliers but haven't seen them in a long time.

 

[wellsc1]

Re: Safe to unhook plug wires while running?

It's a good way to find a fouled plug or bad cylinder, but be quick about. My mechanic is all business when testing by this method.

Regarding the yellow gloves by the power company guy. My experience with a power company years ago showed how they test those gloves with high voltage, trashing the ones that failed. They know their business, trust me.

 

[Rick.]

Re: Safe to unhook plug wires while running?

There are such things as insulated gloves and special pliers for such things. But no way in heck are you going to see me grab and disconnect a spark plug wire bare handed. Especally on that motor. That thing can throw a one inch long spark with ease.

As an aside, the Florida Power and Light guy came out to do some service work on our underground power lines. I watched as he removed the lid from a hole in the ground, reach in and pull the wires out and do what he had to do (the power was on). His only protection was some big yellow gloves. He was on his knees on the wet ground and the hole was full of water!!!!!! I'd rather face a roaring lion than do that. I HATE getting shocked.

Oh yeah, back on topic---the fool proof way is to disconnect the wire and ground it or attach a spark checker BEFORE starting the engine. It is a severe strain on the ignition system to just remove the wires without giving the spark someplace to go. Or if you must disable the plug while it actually is running, make up a temporary exposed jumper plug wire so you can short it out with a screwdriver to ground.

Well I learned something again today. Thanks for that F_R. I'm tempted to call you a sissy but I would never do that. I'll be looking for some gloves and the fun will be over. Rick.

 

[Jonathan3206]

Re: Safe to unhook plug wires while running?

Oh trust me it hurts..

I was working on my work truck and was holding the plug with plyers and my finger sliped off the rubber and touched the plyers and it got me. From my finger to my elbo.

SUCKS

 

[tmcalavy]

Re: Safe to unhook plug wires while running?

Put a spark checker/tester in line like FR suggested and you don't have to risk it...unless you want to ask an in-law to hold the wire while you turn the key or pull the rope.

 

[Fl_Richard]

Re: Safe to unhook plug wires while running?

That bugger will knock the snot out of you!

I use kids for that! teaches them a lesson. Dont hold anything electric that dad says wont hurt you.

 

[jtexas]

Re: Safe to unhook plug wires while running?

For about $2.00, I got a plastic "spark plug boot" tool at autozone, made for the purpose. No more electroshock therapy for me.

Alternatively, you could ask your mother-in-law to help out...........

 

[75-JOHNSON]

Re: Safe to unhook plug wires while running?

well thanks for that guys! i did it what i thought was the safe way and just disconected the wire before i started the engine.

 

[Sea18Horse]

Re: Safe to unhook plug wires while running?

Well, actaully that's not a real good idea either. As F_R and others pointed out above, that is a very powerful ignition system. There is a good chance that the spark will find a path to ground if you leave it disconnected. Chances are that path will be right through the body of the coil. Or into a near by wiring harness. Better to disconnect from the plug and ground it first. Or get a spark checker as suggested above. You can also use a short piece of black vacuum hose to put inline with your spark plug and use a test light to ground each one, one at a time. (Make sure the test light works first! )

Cheers..............Todd

 

[Zeeter]

Re: Safe to unhook plug wires while running?

I do it all the time but as said, it's not safe. You won't kill a healthy electronics system but make DAMM sure your feet are dry and you use insulated pliers. The spark checker is defininetely the way to go.

 

[lowkee]

Re: Safe to unhook plug wires while running?

You can remove the wires no problem with this tool:

It won't do any damage to remove the wires while running. Easy way to diagnose bad wires and (worse case) cylinders with low/no compression. The tool is called 'Spark plug pliers'. If you do decide to remove them while running, do not lay the wires down, as the spark will still happen if it finds a ground nearby. Lift the wire off the plug, then put it back on. You can't (safely) lay it down on anything but the cyl head, and a running engine often just rattles the wire off, making it fall onto a less desirable component. So no dropping wires after removal.

 

[coolguy147]

Re: Safe to unhook plug wires while running?

ummm i remember i did it on my little 10hp and i got shocked really really bad!!! no protection i wont be doing that again so i know the top cylinder was sparking good didnt want to check out the bottom though

 

[petryshyn]

Re: Safe to unhook plug wires while running?

I hate to disagree, lowkee, but F_R is right. Removing a plug wire to open air can easily damage the coil and in some cases, even the CD pack.

Here is a safe and easy way to kill a cylinder. Bend a piece of wire as shown in fig001. (I use MIG wire) Insert in into the plug boot till it reaches the plug depth in fig002. Ground out the wire when you want to kill this cylinder fig004.

I must have too much time on my hands....

 

[Rick.]

Re: Safe to unhook plug wires while running?

petryshyn's Avatar
petryshyn: That is an excellent way to do it and more fun in the long run. Thanks for sharing your pictures. This is a great site to learn from and I just learned something. Rick.

 

[lowkee]

Re: Safe to unhook plug wires while running?

I hate to disagree, lowkee, but F_R is right. Removing a plug wire to open air can easily damage the coil and in some cases, even the CD pack.

I'd like to hear a technical explanation as to how this is possible, since you are essentially disconnecting the circuit. Without a ground, the coil (it is really a transformer, the term 'coil' is misleading) will simply turn off. The high voltage field will simply collapse in an instant (at 50KV+ that instant is mighty quick), ready to be reactivated for the next spark cycle. By the 'coil damage' logic, you could never use any electromagnet without it being destroyed when unplugged.

 

[petryshyn]

Re: Safe to unhook plug wires while running?

Because of its design, an electromagnet never produces the high voltage that a coil can. A coil has a primary and a secondary winding designed to reach a high voltage.
When a spark plug is in a circuit, it acts as a regulator (or governor sort a speak) As voltage is being induced into the secondary winding (from the primary magnetic RISE) it will only rise to a level required to jump the gap of the plug and complete the circuit. (approx 4000-12000 volts depending on fuel mixture between the plug electrodes) If you remove the plug from the circuit, there is no easy path provided for the circuit, so the voltage is allowed to rise to its full potential (30000-50000 volts) This dangerously high voltage may find a path through any nearby conductors leading to engine electronics. It also may take a path to ground through the very same coil that created it, leaving a burn mark or carbon trace behind making it easier for the next "bolt of lightning" to take! thus coil damage.... This coil damage may not show itself today or tomorrow, but the carbon path, over time, will become a easier path to take, over and above a worn plug or a lean mixture between the electrodes. And of course, this always happens on the other side of the lake!!