Removing Ignition Coil cables with engine running

[hamonrey]

I saw this guy doing it with an E46 M3.

[ame]http://www.youtube.com/watch?v=z37jl4HXQjg[/ame]

I have a E36 328i. For testing purposes is it okay to disconnect the cable from the ignition coil with the vehicle running. The only reason I ask is his model has some easy peasy clip on and clip off things. Mine will require raising the harness and then unplugging and replugging, which could cause arcs and such.

[Sprouty88]

I dont reccomend this at all.....

[flyfishvt]

What exactly are you hoping to accomplish with this? What info are you hoping to get that you can't get some other way?

[Sprouty88]

Actually i guess you could do this. Still probably potentialy dangerous. But if you have a misfire from a coil pack. You probably have high milage. And all the coil packs should be replaced.

[hamonrey]

What exactly are you hoping to accomplish with this? What info are you hoping to get that you can't get some other way?

Honestly FREE DIY troubleshooting is all I hoped to gain. Real time differences are much more noticeable than turning it off and restarting with the same troubleshooting techniques. I'm only asking you guys as I don't want to mess up anything. So any input is very much appreciated. It appears that the first 2 folks say it is stupid to do this. I would never pull a stick of RAM out of a computer while its on either, but that video made me think about trying this.

[UnderCoverGuy11]

This is actually a pretty common test I've read about to find dead cylinders. Alot of people do this if you can't tell which cylinder is misfiring or is dead. I personally haven't performed it but some shock proof gloves and you should be fine.

[Auto Parts Guy]

Go to autozone and they will do an OBDII test and tell you which cylinder is misfiring. free.

[Toby B]

I would not try that, myself.

Great way to fry the electronics...

t

[gc325is]

There are 6 coils in a 325 BMW each work on a 12 V pulse from the DME. All he is doing is pulling off the 12 Volt source. It's the other end where the plugs are that's high voltage. This help determine if your mis fire is from a bad coil, plug or plug wire and not on the computer end. You could do it another way but that involves a lot of part swapping.

[TheDurk]

There are 6 coils in a 325 BMW each work on a 12 V pulse from the DME. All he is doing is pulling off the 12 Volt source. It's the other end where the plugs are that's high voltage. This help determine if your mis fire is from a bad coil, plug or plug wire and not on the computer end. You could do it another way but that involves a lot of part swapping.

I agree. If pulsing to an open circuit caused problems, there would be a lot of dead DME's in this world. Pulling a 12V primary is a piece of cake. Loosen the plug beforehand and doing it with bare hands would not be a problem. I've done this a lot on tractors and cars with dizzies to find the missing cylinder and you can get a very nice jolt from a high-voltage secondary if you are not careful--whole different thing.

I've never had a misfire on an OBDII BMW, but I know Toyota's frequently misfire without setting a code. (My DD is a '99 4Runner). It has to get bad enough for the computer to sense it.

[Zodiacbw]

+1 on the Toyotas misfiring without a code. Replaced a couple coils on my Dad's sequoia this way, eventually went ahead and replaced them all after 3 died within a couple months. This just reenforces the point, if they're getting to the point where one or two are going bad, just go ahead and replace them all.

Pulling the connection to the coil is a good way to find a dead or weak coil.

[JDStrickland]

I saw this guy doing it with an E46 M3.

http://www.youtube.com/watch?v=z37jl4HXQjg

I have a E36 328i. For testing purposes is it okay to disconnect the cable from the ignition coil with the vehicle running. The only reason I ask is his model has some easy peasy clip on and clip off things. Mine will require raising the harness and then unplugging and replugging, which could cause arcs and such.

What do you hope to accomplish?

If you are having a misfire that you can feel, the car should be feeling it too, and reporting it via the Check Engine (SERVICE ENGINE SOON) light.

If you are having a misfire from a single cylinder, then swap the coil with another cylinder and see if the problem moves with it. If yes, then the coil or the boot is bad. If no, then the plug or fuel delivery is the problem.

I doubt that it is possible to feel a misfire in your butt and not have it reported by the check engine light. Most report a misfire noted by the check engine light that they cannot feel in their butt. We see P030n (where n is the cylinder number) codes here where the poster says, "the car runs fine, I can't feel a thing."

[randomy]

I can't say anything more than what has already been advised, but I want to back-up that advice. I do not think it would be a good idea, and I feel that whatever diagnostic purpose you are wanting to achieve, can be done more safely, more accurate, and at no-cost still.

[hamonrey]

Thanks for the input y'all. I'm going to do the smart thing and not mess with it. Something I think I left out of my initial post, I was told that cylinder three was misfiring. I changed all the plugs and swapped ignition coil 3 with 4 and was thinking that test that guy was doing in the video would save me the $40.00 my mechanic charged me to run the initial scan that would hopefully say 4 was now misfiring per my swap. I don't see where Autozone offers the scan service for free, but I'll call and see what's up. P.S to the gentleman speaking of the check engine light. My car has a check control light and my OBC is pixelated. I hope to fix that soon, though I ordered the wrong OBC, needed an 11 button and ordered an 18 button like a clown.

[coolpizzadude]

You should be ok. Just make sure you don't shock your self. These things give you one heck of a jolt.

[epmedia]

I'm thinking it should be ok too, IF THE COIL AND SPARK PLUG IS GROUNDED properly, AND IF YOU DO NOT HAVE A HEART CONDITION, AND THE COIL IS NOT ARCHING TO GROUND.

Wear the gloves and test the coil by use of a screwdriver and look/listen for sparks first, just in case (in case the coil is cracked/arching sparks).

You'll get comments from those that have been zapped by 50K volts, "it's not so bad if your not sweaty".

50K volts will throw you a couple feet, just beware

[coolpizzadude]

I'm thinking it should be ok too, IF THE COIL AND SPARK PLUG IS GROUNDED properly, AND IF YOU DO NOT HAVE A HEART CONDITION, AND THE COIL IS NOT ARCHING TO GROUND.

Wear the gloves and test the coil by use of a screwdriver and look/listen for sparks first, just in case (in case the coil is cracked/arching sparks).

You'll get comments from those that have been zapped by 50K volts, "it's not so bad if your not sweaty".

50K volts will throw you a couple feet, just beware

Lol I made the very stupid mistake of testing the spark with my hand like I do with small engines. My hand was sore for almost a day.

[notforyou]

There are 6 coils in a 325 BMW each work on a 12 V pulse from the DME. All he is doing is pulling off the 12 Volt source. It's the other end where the plugs are that's high voltage. This help determine if your mis fire is from a bad coil, plug or plug wire and not on the computer end. You could do it another way but that involves a lot of part swapping.

I agree. If pulsing to an open circuit caused problems, there would be a lot of dead DME's in this world. Pulling a 12V primary is a piece of cake. Loosen the plug beforehand and doing it with bare hands would not be a problem. I've done this a lot on tractors and cars with dizzies to find the missing cylinder and you can get a very nice jolt from a high-voltage secondary if you are not careful--whole different thing.

I've never had a misfire on an OBDII BMW, but I know Toyota's frequently misfire without setting a code. (My DD is a '99 4Runner). It has to get bad enough for the computer to sense it.

Like they said, There is no reason you cant pull the cables off the spark plugs, its been done this way for 100 years to diagnose misfires. OBDII or not, its the quickest way to find a misfire. Its actually safer on Coil-Over-Plug engines than it is distributor-based engines because the spark comes out on the bottom of the coil where it connects to the plug. Distrib engines can hurt when doing this.

[kampy]

I have pulled the wires off of ignitors for years. You just breaking a 12v path to ground. will not hurt anything, including you.

[JDStrickland]

Thanks for the input y'all. I'm going to do the smart thing and not mess with it. Something I think I left out of my initial post, I was told that cylinder three was misfiring. I changed all the plugs and swapped ignition coil 3 with 4 and was thinking that test that guy was doing in the video would save me the $40.00 my mechanic charged me to run the initial scan that would hopefully say 4 was now misfiring per my swap. I don't see where Autozone offers the scan service for free, but I'll call and see what's up. P.S to the gentleman speaking of the check engine light. My car has a check control light and my OBC is pixelated. I hope to fix that soon, though I ordered the wrong OBC, needed an 11 button and ordered an 18 button like a clown.

CHECK CONTROL does not matter. It does not tell you OBD II information when it works, so whatever it tells you when not working won't help.

If you had a misfire on 3, and swapped the coil to 4 and now the misfire is on 4, then you found a bad coil or a bad boot. (The boot is the connector between the coil and the plug, it fits the circuit position that was formerly taken by the spark plug wire.)

Pull the offending coil again, #4, and another coil but not #3, and remove the boots and swap them, then put the coils back in the same places. If the misfire moves again then the boot is bad, if the misfire remains on #4, then the coil is the problem.

Autozone (in California) does not pull your codes, you have to do this yourself. But they do provide the scan tool so you can do it. I do not know what happens in your state. Call Autozone and ask them if they loan tools for special projects, then ask if they have the scan tool in the loaner inventory.

When you turn the key on, but before Engine Start, you have an indicator on the left side of the instrument cluster, bottom row, that says CHECK ENGINE or SERVICE ENGINE SOON (BMW uses both messages, and they switched from one to the other at some point, I don't know when or why, but CHECK ENGINE is the preffered and most common way to refer to this light.) If this light is on AFTER engine start, then your car is telling you that there is an OBD II code stored, and the code tells you something about the condition of the engine management and emissions control systems.

[Schramm]

I don't see a problem either...

We did essentially the same thing on our CNG engine in our lab, we ground out the spark plug (disabling it) to find the friction in each cylinder. While running. Just be sure not to let it run too long without spark cause you'll be dumping fuel into your exhaust. That could cause a bang. My co-worker has a neat muffler in his office from that now.

[eric325]

I'm not going say do or don't...
But I have done this with no adverse effects.

[hamonrey]

.

[epmedia]

Lol I made the very stupid mistake of testing the spark with my hand like I do with small engines. My hand was sore for almost a day.

It's quite a sensation
My worst (not my first) experience was with a '76 two cycle motorcycle running on fumes (about 15k rpms). I was worried about the engine so I pulled the plug wire off, and that sucker zapped my hand all the way from 2 feet away.