The 5th out of 6 plug connectors has a spark which is visible everytime the cylinder fires!!!

I have just put in a new set of plugs before I brought the car out of winter storage......

What have I done here???

Please help me!!!!

Thank you,
Mike McKinney

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1989 300CE - 269,000 km
1994 SL600 - 59,000 km

I just pulled out the plug and it is fine, slight brownish colour on top, no carbon deposits or oil deposits....

The plug connector has a little hole in the rubber boot, causing some spark to go through it......

This must be the cause of the shaky idle right???

Please advise guys, much appreciated.

Mike McKinney

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1989 300CE - 269,000 km
1994 SL600 - 59,000 km

Plug wires are so susceptible to breakage they make plug pulling plliers to protect the leads. Did you use plug pulling pliers? did you yank on the wires?

A torn lead can cause idle problems.

Yes I did pull the last two connectors out with pliers......

Used electrical tape to cover rip in plug connector boot, reinstalled and it idles fine now.

I will order a new set of plug wires on Monday to make sure my idle stays smooth as silk...

Thank you for your help Ethan.

Mike McKinney

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1989 300CE - 269,000 km
1994 SL600 - 59,000 km

mike..you can save youself a few bucks by buying just the plug connector ends. paul

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Paul Roberts
Mercedes Centrum Inc.
Bellevue,WA.

Those plug wire ends have a ceramic (I think) fitting inside the rubber. If you crack this part while trying to pull the wire out it will cause mis-firing. Just replace the plug connector end like Paul suggested. The wire itself screws into the plug connector -- just push the wire deep down inside the connector and start rotating clockwise. I think it's like $10 from Fastlane.

Good luck!

~Paul

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'91 300E, 208k miles

See my reply to your other post. The act of removing and replacing spark plugs bears a significant risk of causing these failures no matter how skillful one is.

We are now replacing the plug end under the three coils on all E320 (or other HFM 104 motors) that we replace plugs on due to the fact that at least one in twenty won't make it through the operation. This means that about every third car will wind up with a intermittant misfire that is almost impossible to scientifically diagnose after plug replacement. The other motors with plug wires are very easy to diagnose so we don't regularly shot gun them. We are starting to replace in groups such failures as we charge more for the diagnosis than the cost of the connectors.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

SB,
I have just replaced the 3 coil boots on a 104 and happen to notice that the replacement [ Beru] coil ends were about 1/3
of an inch shorter than the Bosch I was replacing. [ same part #]
Have you been using the Beru and if so, no problem?
I am sure the coil spring compresses on the plug tip, but by how much can't be measured.

Thanks.
Arthur Dalton

Sounds like a good question, unfortunately I almost never actually replace parts anymore. I only do diagnostics and even there I have an assistant that hooks up the tooling I require. About the only bolts I turn anymore are those involved in doing wheel alignments which I usually do 3-8 of a day.

I like doing alignments as it is the last "tunable" item on a modern car. I get great pleasure solving problems through adjustments.

The last 104 we put connectors on I happened to be standing next to my assistant and I did notice a manufacturing difference between the new end and one that he had already replaced. I will have to take a better look next time. Sorry I don't have a better answer.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks.
I always thought I would enjoy the alignment trade myself.
Something attractive about it.
Actually have made up a few of my own tools for the 113 chassis. Have posted plans for one to do the rear axle centralizing on the group.

Anyway, to my surprise, after changing the boots to 2,4,and 6,
I pop up codes 21,22,23 on the HFM ignition module [ socket #8]
Coil output low, wires , plugs.-- seems too much of a coincidence to me.
Guess I will have to do some test...
Forunately, I kept a set of the 1,3, and 5 wires , so I guess I can substitute them for the coil tower ones to take some readings.
Is that how you would get to the secondary on the 104 set-up?
Again,
Thank you

Confidence in reading secondary patterns comes from experience. I do not have much with 104 motors. I have used inductive pick-ups somewhat like the old GM HEI distributor adaptors most scopes used to have. The patterns have been poor and only one at a time, so I haven't liked using them for the normal things I would do with secondary. So far the best results have been to look at the primary and/or to current ramp the primary. I just bought one of the new Vetronix MTS5100 scopes and will try and see what I can get hooking to the plug wires. I presume that this is like waste spark systems and both plugs should appear on each wire. The question will be what to use as a sync pulse.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

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Yes, being a 2 plug series circuit should show on either side as the coil circuit is a complete loop.
I would be interest in anything you may find/come up with.

I'm replacing plugs and was advised to use Bosch Platinum WR 9 DP type with gap of .032. Is this correct. Having trouble locating document specifying gap measurment. Any help appreciated.
Thanks for the wire pulling advice as I'm trying to be super sensitive to how I remove them.

Don't waste your money on the Platinums. Not only does MB specifically recommend against there use, but they are well known to cause numerous driveability problems. Use the copper core that was standard.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks for the quick response. People who don't mind helping people, what a concept. Anyway being impulsive self I have all ready installed four of eight plugs and now must ask if I should pull them out ?? or continue. I'll wait this time. Is .032 gap correct ? Also have 1 gallon of MB antifreeze. Will mixing with one gallon of distilled water achieve level of coolant necessary if I drain radiator? Again thanks for the help.