Risk of pulling single spark plug wire with motor running

[hkeiner]

I have read about one troubleshooting test where you pull the spark plug wire (one at a time) from the spark plug while the engine is running and monitor what happens. If the motor idle speed drops uniformly for each spark plug wire pulled (cylinder), then that is a good thing. If the idle does not drop for any particular spark plug wire (cylinder), then that my indicate a problem on that cylinder. This test makes a lot of sense to me. In contrast, I have read elsewhere that it is very important to ground spark plug wires when they are disconnected from the spark plugs and you are turning over the motor. This is often mentioned when directions for performing a compression test is given. I presume that this caution is given to avoid damaging the ignition system.

The directions for the above two tests seems to be in conflict with each other regarding the grounding of the spark plug wires. Since I plan on performing the former described test for the first time, I thought it best to better understand the techinque and risks to the ignition system when pulling spark plug wires while the motor is running, if there is any. Also, how do you best avoid getting a jolt when handling the wires.

Thanks in advance for any thoughts on this.

 

[Silvertip]

Re: Risk of pulling single spark plug wire with motor running

A good electricians pliers works well for this. One of the old springy style clothes pins works as well. You don't have to let the engine run for any length of time with the plug wire off. It is immediately apparent whether or not the cylinder is good when you disconnect the wire.

 

[jeff_smith_0423]

Re: Risk of pulling single spark plug wire with motor running

i was also afraid of getting a jolt, until i had no other choice but to perform the test.. I just gripped the boot and yanked with no ill effects - (other than the motor dying since it was only running on 2 of 4 cyls and having only one with fire couldn't keep it running.)

 

[j_martin]

Re: Risk of pulling single spark plug wire with motor running

i was also afraid of getting a jolt, until i had no other choice but to perform the test.. I just gripped the boot and yanked with no ill effects - (other than the motor dying since it was only running on 2 of 4 cyls and having only one with fire couldn't keep it running.)

Yer lucky. It can jump over 1/2 inch and knock you on yer *****. It's possible to quit living also.

They make an ignition plier for that specific task. Well insulated and ideally shaped to pull the boot without damage.

hope it helps
John

 

[Hoopie]

Re: Risk of pulling single spark plug wire with motor running

I use a pair of welding gloves with a pair of rubber handled plyers. If you do get zapped you will never forget it,it hurts like h3ll. Good luck be safe.

 

[j_martin]

Re: Risk of pulling single spark plug wire with motor running

Watch out hoopie, you'll get the **** treatment for your nasty language.

 

[TOHATSU GURU]

Re: Risk of pulling single spark plug wire with motor running

If you have CD ignition your looking at 35,000 to 55,000 volts. It's not pleasant...The first time. But, you get used to it after awhile. Now I kind of enjoy it...ZZZZZZZZZZZZ Another brain cell gone

 

[achris]

Re: Risk of pulling single spark plug wire with motor running

These are what I use... They are HRC fuses pullers. Never had a jolt from an outboard, and don't plan on it... I hate jolts!!! I strongly recommend against using your hands. The CDI systems can produce as much voltage and way more current than the EHT in a colour TV. When colour TVs first came out some of the old school techs weren't discharging the EHT before disconnecting it... and some of them 'quit living' .......

 

[rnorrk]

Re: Risk of pulling single spark plug wire with motor running

easy way of doing a cyl balance test use a test light if access is tight install a short lenght of vacum hose between wire and spark plug just dont damage wire .slide under it to kill cyl one at a time then compression check , spark out put check either HEI or STANDARD tester

 

[SgtMaj]

Re: Risk of pulling single spark plug wire with motor running

I've been hit by spark plug jolts before, it was just a light tingle really, but it might be a little different since it was on my lawnmower. On the other hand, I might have a skewed perspective as I've been electrocuted more than a few times before. I put in about 4 years as a PBX tech, and durring that time I was struck by lightning once, hit with 240vac 15amps (that was the worst by far) once, and 120vac 4-5 times, and of course 90vac almost every day, but that was like .3 amps so that was just a tingle in the funny bone. The only time my heart ever stopped was when I was hit with 240 volts. Fortuneately I was working in the new wing of a hospital.

You know, it is a miracle I survived that job... the electrocutions were only one part of the drama, I was dumped out of a cherry picker, fell off an xtn ladder (or as my coworkers said, rode it to the ground), and then there were the crawl spaces, and all the venemous creatures in them.

 

[achris]

Re: Risk of pulling single spark plug wire with motor running

I've been hit by spark plug jolts before, it was just a light tingle really, but it might be a little different since it was on my lawnmower. On the other hand, I might have a skewed perspective as I've been electrocuted more than a few times before. I put in about 4 years as a PBX tech, and durring that time I was struck by lightning once, hit with 240vac 15amps (that was the worst by far) once, and 120vac 4-5 times, and of course 90vac almost every day, but that was like .3 amps so that was just a tingle in the funny bone. The only time my heart ever stopped was when I was hit with 240 volts. Fortuneately I was working in the new wing of a hospital.

You know, it is a miracle I survived that job... the electrocutions were only one part of the drama, I was dumped out of a cherry picker, fell off an xtn ladder (or as my coworkers said, rode it to the ground), and then there were the crawl spaces, and all the venemous creatures in them.

Note to self - Stay away from him ^^^^

I've also had a few electrical belts. Lawnmowers, 240Vac, I had a 440vAC one too, but the worst was from a CDI I built myself. The engine had a miss and I was trying to isolate which cylinder, so I was pulling the plug leads off with a pair of pliers. Found out pretty quick that there was a pin hole in the handle insulation!!! I think I got hit about 10 times... MAN, THAT HURT!!!

Chris............

 

[renny1]

Re: Risk of pulling single spark plug wire with motor running

i was working on my engine whilst on the jetty and was pulling pug wires with insulated pliers hanging off the back of the boat and yes yu guessed it there was a hole and zzzzzzzaaaaappppp i went for a swim so now i use plastic

 

[achris]

Re: Risk of pulling single spark plug wire with motor running

i was working on my engine whilst on the jetty and was pulling pug wires with insulated pliers hanging off the back of the boat and yes yu guessed it there was a hole and zzzzzzzaaaaappppp i went for a swim so now i use plastic

ROFLMAO... Sorry Renny, that's a good one....

 

[SgtMaj]

Re: Risk of pulling single spark plug wire with motor running

Note to self - Stay away from him ^^^^

Yeah no kidding... thank goodness I left that job. Havn't had any such brush with death since.

Actually, it's not so much me that you want to stay away from... in most cases, it somehow ended up being the electricians fault. When I was struck by lightning, the bolt hit just outside, but the jolt came up from ground to a box that had no conduit, and shouldn't have been grounded, but some electrician decided to wire it up to the electrical ground. (The funny part is, that was in a church. You know that whole joke about being struck by lightning in a church... yeah. Even the pastor got in a few rounds of that joke after making sure I was ok.)

When I was hit with 220, I was just pulling cable in the ceiling, when somehow, the electrician managed to electrify the whole ceiling droptile grid. You better believe I cussed him up one side and down the other.

A lot of the 120 hits were just shorts between electrical and telephony cabling. I think the electricians have to share at least some of the blame for those.

Can't really blame them for the rest of it though... my co-worker dumped me out of the cherry picker (or tried to anyway, I hung on for dear life when he hit the release by mistake)

The ladder was my fault, totally.

I blame the exterminators for all the wasps, hornets, and spiders I had to encounter in the crawl spaces.

 

[Motor Boater Bill]

Re: Risk of pulling single spark plug wire with motor running

My best hit was putting a new motor on a blower in my dad's attic. I had no shirt on, was sweating like a pig, had my back pressed against a metal duct (ground) and told dad to shut off the breaker. He turned off the wrong one. When I put the screwdriver on the terminal (with both hands) I got it through my whole body. The next thing I knew I was standing up, with my feet each on joists (so I didn't go through the ceiling below) and my head cocked over just enough not to hit the slope of the roof. Funny how your body can do things without your brain being in on it!

Also, I learned working on cars that you don't get jolted by the spark unless you are touching the vehicle (grounded). Of course, a boat in the water offers many paths to gound...

One of the best diagnostic tools I own is a little spark tester that you put in between the plug and the wire. A little bulb inside flashes with each spark. Way better than pulling off wires while the motor's running! $6 at Harbor Freight.