Sudden rough running - bad plug wire 95 E320?
Thread Starter
Junior Member
Joined: Nov 2005
Posts: 18
Likes: 0
1995 E320 Sedan 120K
Sudden rough running - bad plug wire 95 E320?
I started my 1995 E320 (126K) on Saturday and it was running very rough - like it had a bad plug- but I had just replaced the plugs a week ago. I exposed the spark plug wires on top and pulled the #1 wire...no change. A culprit. I changed the plug and no difference. I hooked my timing light to the wire and got nothing. I got a flash of the timing light from the other plug wires. I had a donor engine (1996 C280) that had the exact same ignition coils (part number) and wires. Swapped out the #6 coil and the #1 wire and fired it up. Success..ran good. The next morning I start it up and drive off to work. About 7 miles out the engine begins to run rough again and I limp back home. I plan to open it up again this evening to test #1 and the other wires. Any one else have this happen to them? I will replace the fuel filter this weekend to eliminate that possibility but it definitely felt like an electrical failure (but only like it was one cylinder and not two which leads me to believe it is a wire and not one of the three ignition coils).
What is a good brand of plug wires to put on it if I replace them all?
Any thoughts are appreciated.
What is a good brand of plug wires to put on it if I replace them all?
Any thoughts are appreciated.
Thread Starter
Junior Member
Joined: Nov 2005
Posts: 18
Likes: 0
1995 E320 Sedan 120K
re: deteriorating engine harness.
You may be right but I can't say for sure yet. After I limped home, I opened it up and then replaced the lead that runs from the spark plug coil that sits on #6 to #1 (yes, I was not getting any indication that there was voltage in the wire again) and started it and it was not missing. When I then put the cover back on, it was missing on #1 again...ggrrr. So this time, I pulled all connections off and applied some dielectric grease to all contact points and reassembled with the same components but without the cover in place and it ran without the miss. I drove it about 12 miles at speeds up to 70 mph without a problem. I suspect I did something when I replaced the cover and must be more careful this time.
However, I did notice that when I put my timing light on each of the spark plug wires that run from the spark plug coils, #1 exhibited a fairly steady strobe (couple of hiccups but no noticeable misses), #3 exhibited a steady and very rapid strobe (almost 2x as fast as #1) and #5 exhibited an erratic strobe but without exhibiting a miss. I suspect it may be something I did to cause the various results.
Anyone have any idea if these symptoms are connected? Could this be a faulty Crank position sensor? I'm not getting a Check Engine Light CEL at all.
However, I did notice that when I put my timing light on each of the spark plug wires that run from the spark plug coils, #1 exhibited a fairly steady strobe (couple of hiccups but no noticeable misses), #3 exhibited a steady and very rapid strobe (almost 2x as fast as #1) and #5 exhibited an erratic strobe but without exhibiting a miss. I suspect it may be something I did to cause the various results.
Anyone have any idea if these symptoms are connected? Could this be a faulty Crank position sensor? I'm not getting a Check Engine Light CEL at all.
Newbie
Joined: Feb 2007
Posts: 10
Likes: 0
If you haven't replaced the wiring harness yet, stop wasting your time checking anything else out. If you have replaced the wiring harness, it may also be your throttle actuator. Both had the same crappy deteriorating wire.
Thread Starter
Junior Member
Joined: Nov 2005
Posts: 18
Likes: 0
1995 E320 Sedan 120K
And the Answer is.....Wiring Harness!!
The harness was unbelievable. I replaced all the wires from the contact points on the spark-plug coils to a point just before the wires were restrained under a saddle clamp by the firewall. I slid shrink tubing down as far as I could and buttoned it. When I initially started the engine, everything was fine and then it started running rough. I reached behind the point where the wires on the harness (near the firewall) bend up 90 degrees and then towards the battery. As I did that, it quit missing and so I figured that there was another fault there. I slit the cloth covering from the point where I had soldered before over to the point where the wires went through the wall toward the battery area and soldered in a jumper for just the 12 volt wiring for the #1 & #6 spark-plug coil (pure black wire). It is running fine now and I think it will hold (I hope). I have a donor wiring harness from a 96 C280 that I am going to remove from the engine and them carefully analyze and replace all the wires. If it is similar to the one I have, I will replace it with the necessary modifications to the end/fittings as needed.
Thanks everyone for your help!
Thanks everyone for your help!
Senior Member
Joined: Jun 2006
Posts: 303
Likes: 1
From: Northern California
It changes all the time
TOLD YA. I don't think the wiring harness from the C class is going to work, but if you try to make it work, check the production date on the door post. The registration may say that the C class is a 1996, but if the production date on the door post says 1995, it is a 1995 and subject to the same deterioration problem.
Trending Topics
Thread Starter
Junior Member
Joined: Nov 2005
Posts: 18
Likes: 0
1995 E320 Sedan 120K
C 220 harness just as bad
I inspected the C220 harness and it is just as bad. I'm pulling it off and will lay it out and decide if I should rebuild it or not. Does anyone know where I can find the electrical pin-outs for these two harnesses? I don't have the body for the engine so I can't determine the production date but I'm sure the vin # is somewhere on the engine...will look today. The battle continues.....
MB World Stories
The Best of Mercedes & AMG
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)
Verdad Gallardo
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
Junior Member
Joined: Sep 2008
Posts: 32
Likes: 0
From: Dallas, Texas, USA
2004 SLK 230, 1992 300E & 400E
I've a 1992 300E and 400E, fortunately, the wiring harnesses in both vehicles had been replaced not long before I purchased the cars..............but.....I'm also the proud owner of TWO 1986 Volvo 240's, and, you guessed it....they have the SAME problem with the environment-friendly, self-degrading, landfill fillers. And, I have "made" two totally complete wiring harnesses for both of those cars, and believe me when I say, I will not do that again. Oh, it was kinda fun sitting up in my shop til past midnight, removing the connectors, crimping wires, stripping wires, getting color coding correct...........heck, even coming up with the proper colored wire, in bulk, was a hoot.
But, I digress. I simply meant to say "It CAN be done."
But, I digress. I simply meant to say "It CAN be done."
