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E34 (1989 - 1995)

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  #1  
Old 01-01-2013, 10:42 AM
BMR_LVR's Avatar
BMR_LVR BMR_LVR is offline
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Testing for impluse/spark on coil-over-plug engines (i.e. M50, M60, etc)

Thought I would share something I learned today when lurking on the E36 forum.

I have always looked for an easy way to confirm spark/electrical impulse on the coil-over-plug design. It’s a piece of cake with engines that have plug wires (i.e. M20 and M30). Just hook up a timing light and put the inducer on each plug wire and you can confirm the impulse. You can pull the plug and ground it to confirm actual spark. I have used a jumper cable to check the actual spark on the M50, but it is real cumbersome, so I won’t go into the process.

Anyway, one of the Festers on the E36 forum had a problem with a no-start on his M50. His son used a timing light to confirm the impulse. I asked how since there are no plug wires. His son simply hooked up the timing light as usual for ground and hot and the placed the transducer over the wires leading to the coil (presumably right at the coil). While this did not confirm a functioning coil or an actual spark, it does confirm the electrical impulse getting to the coil from the DME. You can check the wire to each coil independently and quickly. I like this because it is quick and easy and this confirms that the CPS is sending its signal to the DME and the DME is sending the impulse to the coil. It confirms that the electrical part of a no-start situation is (for the most part) intact and one can rule it out and proceed to troubleshooting fuel delivery.

I remember my indy mech showing me a cool little piece of test equipment that he uses. I did a little searching and found a link to it:

http://www.ebay.com/itm/Fix-Small-En...item3cc33839ec

You simply take the coil off of the plug (leaving the electrical connection intact), insert the device into the coil, clip it to a grounding point (I believe that one of the studs that holds the stud would work) and crank the engine over. This will confirm electrical impulse from the DME to the coil and confirms that the coil is working. It does not confirm actual spark (as in a spark plug failure) nor does it indicate the strength of the coil.

Here is another one that I found that works on the same principle:

http://www.northernautoparts.com/Pro...ctModelId=2431

This one is nice in that it has an adjustable gap feature, but it is also not insulated and one might have a bad day were he to touch the tool during operation.

Anyway, I thought that was some good information to share.
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  #2  
Old 01-01-2013, 05:58 PM
robertobaggio20 robertobaggio20 is offline
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This is a great tool and its cheap. Good find, and good tip on the transducer. I am surprised that it can be adapted for coil on plug systems...the timing light's transducer detects the magnetic field generated as the electrical charge passes through, but this usually only works on distributed charge systems (m20 engines) as the charge itself is high enough to produce a measurable field. The coil on plug system's leads just send an ordinary normal signal to the coil, which then amplifies it internally.

This means that the timing light transducer works well enough to check for current flow along any wire in the car. There is no need to disconnect etc, which can sometimes be very inconvenient. Hmm...

Anyone with a timing light ? Could you check this out ? On both the ignition coil's leads, and on other wires for other devices which should carry current when the engine is running.

Anyway, just to share, one easy way to double check for spark is to merely hold the coil with a spark plug in its boot against the car's body and crank. Holding the head of the coil is safe, the transformer is inside the head of the coil and not outside, this is why you can touch it while the engine is running and you will be fine. If you are concerned, just wrap a cloth around the head and hold it that way. This works for the M20 engine's leads as well, just put a spare spark plug into the disconnect lead and hold it against the car's body, use gloves or cloth to shield your hands in this case. Then have the engine cranked. Yup, this method requires two to tango unfortunately. The workaround where one person is sufficient is to clamp the spark plug with one end of a jump start cable and clamp the other end to a ground point in the car, and position it such that the plug/clamp is vertically above the lead or coil, such that its weight keeps it pressed down into the lead/coil.

Last edited by robertobaggio20; 01-01-2013 at 06:03 PM.
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  #3  
Old 01-01-2013, 06:25 PM
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BMR_LVR BMR_LVR is offline
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Quote:
Originally Posted by robertobaggio20 View Post
.... Holding the head of the coil is safe, the transformer is inside the head of the coil and not outside, this is why you can touch it while the engine is running and you will be fine. If you are concerned, just wrap a cloth around the head and hold it that way. This works for the M20 engine's leads as well, just put a spare spark plug into the disconnect lead and hold it against the car's body, use gloves or cloth to shield your hands in this case. .....
Hello Roberto. I usually don’t like to post something contrary to what someone posts. I have been seeing way too much of that on the Fest of late. However, that being said, I feel compelled to contradict the above statement strictly for safety’s sake. The below statement is quoted from the Bentley manual (page 120-2) and it is not the only warning posted about this issue:

Warnings and Cautions

The DME system contains sensitive electronic components. To protect the system and for general safety, the following warnings and cautions should be observed during ignition system troubleshooting, maintenance, or repair work.

WARNING —

• Do not touch or disconnect any of the high tension cables at the coil, distributor, or spark plugs while the engine is running or being cranked by the starter. Fatal voltages are present.
• Before operating the starter without starting the engine (for example when making a compression test) always disable the ignition. See Disabling ignition System.
I feel that it is irresponsible of you to tell other members something that has the potential of being fatal. You have to keep in mind that a coil could have a crack in it; there may be a break in insulation on a wire etc. and coming in to contact with them could have tragic consequences.

Simple gloves or a piece of cloth will not insulate a person against an electrical current, especially of this magnitude.
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1991 735i - Sold
1992 525i - Sold
1995 325is - Sold
2000 528i - Sold

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  #4  
Old 01-01-2013, 06:52 PM
robertobaggio20 robertobaggio20 is offline
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Hello Steve sir,

Thank you for that explicit disclaimer from the Bentley manual, and I would invite you to post more when you have an opinion that is contrary to another's. Almost all your posts and opinions are well thought out, are expressed clearly and are free of malice. This permits the reader to analyse what you say intelligently, which is critical even if he decides against what you're saying. Contrary opinions essentially demonstrate the veracity of the truth so they are welcome at least in my book.

Let me come to this matter. I have actually seen my mechanic do it this way on the M20 engine. He did not use a glove, just his hand over the m20's lead and held the spark plug within it against the car body while I cranked. Admittedly he could have thicker skin than most but I doubt it.

I personally wouldn't do it due bare handed due to basic fear, but well physical evidence cannot be debated. And if plastic is good enough to insulate wires and coils, do you think cloth would less effective ? This would be the ecology test.

The voltage is extremely high 20k-40k volts, but the current is extremely low...micro or pic amps etc.

General purpose manuals always put in exceptional warnings to idiot proof things, because some of the readers will be idiots, careless or highly inexperienced. This is exactly what I would do if I was publishing a manual for the lay populace, and it involved something that could harm you.

If I wasn't clear enough earlier that ignition coil systems contain high voltages (20k-40k) that can jolt you at a minimum or kill you if you're dealing with a perfect storm, I apologise to you. I assumed that this is generally known.

Last edited by robertobaggio20; 01-01-2013 at 06:56 PM.
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  #5  
Old 01-02-2013, 05:10 AM
snowsled7 snowsled7 is offline
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Cloth is a very poor insulator becaue it is too porous. Rubber is much better as insulation against getting a shock.

That said, it is highly unlikely that the spark from a plug, wire or coil is going to be fatal. If you have a pacemaker...well, then you should avoid all HT electricity. I have been zapped many times by coil voltage. It is a pretty good zinger for sure, usually leading to a bumped head on the hood but, it hasn't killed me yet.
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  #6  
Old 01-02-2013, 05:38 AM
robertobaggio20 robertobaggio20 is offline
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I am going to find a quick and dirty way to test the coils for spark and charge delivery, as the case may be, for the good of mankind (am now in a good for mankind kinda mood). Everyone, please watch this space.

And yes it appears that my hunch was right ! Please see :

http://m.everythingscience.co.za/gra...m-02.cnxmlplus

If the current in a mere electrical wire that feeds an ignition coil is good enough for a timing light, it will might well be good enough for the compass.

Come people ! Anyone with a magnetic compass (not the crap on our smartphones....although......hmmmmmmm.......na.... )....please do this test ! Hold the compass next to the coil's wire and the coil with the engine off, then start the engine and hold the compass next to the wire and the coil while the engine is running, and post your results here ! I will try and find one and do this one my car and post here.
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  #7  
Old 01-02-2013, 07:16 AM
snowsled7 snowsled7 is offline
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Quote:
Originally Posted by robertobaggio20 View Post
I am going to find a quick and dirty way to test the coils for spark and charge delivery,

Why

The test BMR LVR posted is pretty quick and easy. It is the correct way to do it. No need to reinvent the wheel again
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