What are the symptoms of ignition wires going bad? - Mercedes-Benz Forum
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#1 (permalink) Old 05-23-2010, 04:30 AM
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Question What are the symptoms of ignition wires going bad?

I have a problem with rough idle when cold. When the car warms up it goes away. I already had MAF swapped and changed few other things.

My uncle suggested this might be an ignition wires problem. His VW Sharan was working rough when cold and it was a bad ignition wire.

Could it be as simple as that?

I don't know when were the wires last changed on the car. I changed only the plugs quite recently.

Is there any way of checking it before I buy all the pieces to replace ignition wires?

W124 250D 1989 OM602 /
W124 300E 1993 M104 /

250D: Just a reliable N/A diesel
300E -> E36 AMG
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#2 (permalink) Old 05-23-2010, 07:08 AM
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How long since the dist. cap and rotor were replaced? Those wear out after a while and get corrosion on the terminals, before the wires wear out. I would chjeck those before replacing wires. But if you do need to replace the wires, Kingsborne in San Diego, CA makes a set I have bought two sets from them about $100 US a set, and was pleased with the quality and fit. Good luck,
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#3 (permalink) Old 05-23-2010, 08:04 AM
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No cap and rotor on my engine. 1993 M104 is a little bit different in terms of ignition.

Also - I am located in Europe, so I'd rather shop locally.

Thanks for input!

Anyway - I'd like to know the symptoms of bad wires.

W124 250D 1989 OM602 /
W124 300E 1993 M104 /

250D: Just a reliable N/A diesel
300E -> E36 AMG
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#4 (permalink) Old 05-23-2010, 09:21 AM
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Usually if your wires have a bad one or more it doesn't change characteristics when it warms up, it might misfire a little more at higher RPM though. Possible vacuum leak? If the problem only recently started, possibly check that the plugs are the ones that esteemed forum member Jayare recommends, and that the gap is correct. You don't want resistor plugs because these cars wires have resistor built into the end of the wires that connects to the spark plug. They say that platinum plugs have a lower intensity spark, however I used them with no bad result. I have since changed my M104 to a Bosch F8DC4 as per Jayare's recommendation and all is well. Many years ago, I changed plugs on a car then shortly after that, it quit running altogether and we spent countless hours and days looking for the problem, can't remember why but it finally was learned that the plugs were the problem! To check the plug wires, use a volt meter and check the resistance of each wire, they should all be very close in terms of resistance. If one or more are very different than the others...voila. Also look closely at the connections at each end making sure there is no corrosion or damage. I always use white silicone grease on the spark plug end to make sure the wire will remove easily without breakage next time, and I always use anti-seize lubricant grease on the spark plug threads. My 1990 M104 has distributor cap, rotor, and single ignition coil which I replaced with a 60,000 Volt Jacobs Electronics Ultra Coil which gives a very powerful spark. But that's just me. Be very gentle and careful when removing the wires (one at a time so you don't get them reinstalled incorrectly) remember that they are expensive and if they are indeed in good order you don't want to break one of them and then have to replace...Good Luck,

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#5 (permalink) Old 05-23-2010, 09:45 AM
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How about engine wiring harness upper and lower? You have the dreaded 93-95 year car. Pull back some injector insulation and look. Also coil packs being aged can cause alot of problems.
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#6 (permalink) Old 05-23-2010, 11:46 AM
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if your not sure when you changed the wires then i would change them then.
coolant temp sensor. could be telling the cold engine that it is warm, then when it warms up it runs properly.


Quote:
Originally Posted by tonylinc View Post
single ignition coil which I replaced with a 60,000 Volt Jacobs Electronics Ultra Coil which gives a very powerful spark.
how does this work for you.my hotrod has one on it also.
i was thinking of buying one for the benz but did not know if it work.
i find the benz has a low coil output.

did you do anything special to make it work, i thought maybe the coil had something to do with the on board computer.

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#7 (permalink) Old 05-23-2010, 12:52 PM
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Mine being a 1990 has a regular coil instead of the coil paks the later ones have, the Jacobs Ultra coil works very well. Just your pos, neg, ground and high voltage lead. I have used this coil on most of my cars now since the 1980s with much success. Also have one on my 1989 190E 2.6 ~ No problems at all with engine's computer. I had a special coil-to-distributor cap wire made for them by Kingsborne in San Diego for under $20.

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#8 (permalink) Old 05-23-2010, 01:35 PM
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Engine wiring harness changed, plugs changed to correct Bosch F8DC4.

Totally running out of ideas...

W124 250D 1989 OM602 /
W124 300E 1993 M104 /

250D: Just a reliable N/A diesel
300E -> E36 AMG

Last edited by MaxMatt; 05-23-2010 at 01:39 PM.
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#9 (permalink) Old 05-23-2010, 02:24 PM
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Start doing some research on the Inlet Temperature sensor and cleaning the MAF.

'O=00=O' BMW 2002. long live the legend.

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#10 (permalink) Old 05-23-2010, 02:40 PM
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Replaced the inlet temp. sensor last week.

I had the MAF swapped from another car last week as well.

No effect...

Thanks for input

W124 250D 1989 OM602 /
W124 300E 1993 M104 /

250D: Just a reliable N/A diesel
300E -> E36 AMG
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