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#1
11-26-2014, 07:16 PM
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M117 Sparks under hood / new wires, etc.
Hi all,
I'll be honest, I did not search much on this. Just worked on car and need it running peak asap. So pardon my ignorance if this has been answered before please. Starting about two weeks ago, my car was running rough. First at idle. This was typically during rain. So I figured water getting into some electric component, etc. Also thought maybe ignition system. Then it starting running rough at idle all the time - worse when wet - but now all the time. This graduated to beyond idle about a week ago. I finally opened the hood and could hear a snapping sound. It was a spark jumping around the distributor cap. About an inch. Secondary ones in other places. So I figured time for a new cap/rotor/wire set. After all, I know my cap had a crack in it. Well today I replaced the cap/rotor and sire set. All Buru brand. I did not get a chance to do the plugs since I could not find the proper socket. The car certainly starts better and runs much better. No noticeable miss anymore. Off the line its responsive again and overall it feels like it has much more power. But I did a lights out test anyway. I noticed glows all over still. No large sparks. More like when one pulls a band-aid off quickly in the dark. But dimmer. These are located at nearly every spark wire end near the wire hood. And along the coil to cap wire. I tried a jumper to ground the coil to ground, thinking bad ground, but no change. So is some glow normal? I dont want to damage all these new parts in any way. A coil is not expensive, but I would like your input before I toss one in when its not needed.
__________________
1991 560 SEL / 185k miles 1992 750il / 17k miles - project car 
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#2
11-26-2014, 10:26 PM
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The aura (glow) you're seeing around the plug wires if voltage leakage thru the wires. This is just from working on other vehicles as I'm still learning on my 420. In my opinion you shouldn't see this with a brand new wireset but someone with more experience will have a better explanation. I wouldn't think the coil itself is suspect since you're seeing it at the wires themselves.
__________________
1983 300SD 1988 420SEL
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#3
11-27-2014, 06:10 PM
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What you are seeing is corona from high voltage. It is more like static electricity than anything else.
Also, caps rarely "crack" what you are getting is a carbon track across the surface. When voltage jumps the gap, it carbonizes the surface making it easier for the next spark to follow. Be sure to change the plugs now, large gaps stress the car / wires / rotor / ignition coil making them fail sooner.
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#4
11-27-2014, 10:31 PM
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Cracked for sure, the plastic was not even aligned. Pretty sure its been that way since I got the car years ago.
Plugs will be next. By the way, I do feel a shock if I touch any wire. I think I will change plugs soon. I read a bad plug may cause this issue. I will also clean all the contacts and mounting surfaces for the coil.
__________________
1991 560 SEL / 185k miles 1992 750il / 17k miles - project car
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#5
11-29-2014, 08:51 AM
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that happen to me once,I had got Armoall on my engine wires.
__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt
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#6
11-29-2014, 12:33 PM
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Quote:
If you are getting a shock, the wires are leaking. Change the plugs now as you will damage the wires if the plug gaps are very large.
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#7
11-29-2014, 12:57 PM
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agree with the above post. worst case scenario is the ezl unit also.
check the coil where it mounts to the body. any "white" you see on the coil body where there transformer core meets the bracket, that's leaking voltage, also. very common. any extra gap the spark has to jump means more amps from the coil. more amps means a tired coil and the shortest path to ground. that's why the white on the coil and the corona you see around the wires. good luck, chuck.
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#8
11-30-2014, 04:43 PM
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Today was suppose to have some decent temperatures, but not so. I hate not being able to work in my garage! So all I got to was new plugs, no coil cleaning.
But the old plugs had a gap of 0.05 or more in some cases! Im thinking that was the issue from the start. And the old wires, etc were not up to the task to properly insulate. The new wires, being new, reduced but could not prevent the arcing issue. Tonight I will take another look for any glowing. The car is running even smoother now. Fingers crossed.
__________________
1991 560 SEL / 185k miles 1992 750il / 17k miles - project car
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#9
11-30-2014, 05:12 PM
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LYL:
As a matter of curiosity, what are designations of the old and new plugs?
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#10
11-30-2014, 08:35 PM
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If you are going where I think you are, both the old and new are resistor type with "R" in the model number. New ones are NKG 7734 gaped at 0.032". Resistor type was something I verified.
Good news is that the arcing issue is 100% gone. Both when cold and hot. But now I have a new issues to resolve. When I start it up, even when warm, I have about 30 seconds of drivability where I have no decent pickup/power. I could practically stall it out it feels. In fact I tried and pretty sure it back fired a little. Then after that 30 seconds or so, its like a switch if flipped and it springs to life. Idles perfectly smooth, plenty of power after. No misses. So not sure what is up with that, I will have to look at things again. For now I will just take it easy on it of course.
__________________
1991 560 SEL / 185k miles 1992 750il / 17k miles - project car
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#11
11-30-2014, 08:53 PM
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LYL:
You are indeed correct about the direction I was taking. The specified plugs are non-resistor. Why? The rotor has a 1K resistor, each terminal in the cap has a 1K resistor, and each plug boot has a 1K resistor. Adding ~5K more in each plug is too much; the required system voltage, the voltage to initiate the arc, is forced too high, and leads to internal leakage in the coil. The cold drivability matter is likely related to delayed warmup of the O2 sensor, combined with a lean basic fuel meter adjustment.
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#12
11-30-2014, 09:32 PM
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Are they? I thought resistor type was specified! I honestly did not look em up, I just went with what the parts store specified.
Think I should switch? I will have to get around to adjusting the mixture then. I usually use a meter directly with the O2.
__________________
1991 560 SEL / 185k miles 1992 750il / 17k miles - project car
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#13
11-30-2014, 10:13 PM
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LYL:
The plugs specified by Mother Benz are: ...Beru 14-7 DU ...Bosch W7DC ...Champion N9YC All are non-resistor. It is almost inevitable that the folks at the parts store will get it wrong; they are quite likely very nice people, but their look-up information is geared to using what the plug manufacturers consider to be an appropriate replacement for 95% of the engines out there, without acknowledging the 5%. I think it would be well to change to non-resistor.
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#14
12-01-2014, 08:00 AM
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You know, this is sad but Peach Parts list a resistor plug as the correct plug for his car. So sad. So sad.
PaulM
__________________
84 500 SEL (307,xxx miles)
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#15
12-01-2014, 05:21 PM
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I wouldn't consider a resistor plug on this system too high. At ~ 25 KV , 5 K Ohm isn't much. I am assuming that these cars use solid core wires correct? If so that gives the stock system 3 K Ohm and perhaps 8 K ohm with resistor plugs. A typical American car has resistor wires and plugs ( Even point type ) with a longer wire reading 12K ohm.
I haven't measured a resistor plug in ages so I can't confirm the 5 K value. ( Sometimes the resistor would fail open ) I'd suspect the market for non resistor plugs is pretty small so some substitution is going to occur.
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