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.

 

I like the bosh line of plugs but if your plugs were past their life cycle I would suspect the coils and wires. Heres a quick trick with one new coil check with a timing light as you did before (can also use a circuit tracer) if you notice a brighter faster more consistant flash (or beep) then is present with the new coil likely cause is week coils you can move to the furthest part of the H/tension leads if coils look good to see if they are bad. Of course an OHMs test is the best for leads and spark jump for coils.

 

Hi Had the same problem on 95 280e, it sounds like the same thing ,it turned out to be the feed wires for the injection connections they become brittle and the covers tend to break down or melt due to engine heat buildup quite a few people in uk have had same problem.Check the wires coming from ecu(in plastic cover along top of engine)two of mine had melted and had a slight split allowing wires to touch,I sorted the problem by covering all the feeds with heat resistant tape,problem sorted,alternative to self fix is new loom BIG MONEY.Hope this helps. 1 hour and 5 pounds,worth a try.

 

all 1995 benzes had a problem with bad engine wireing harnesses. the wires get brittle and crack. very very common. its best to replace the harness first because it can cause various issues and youll be chasing your tail trying to figure out what the problem is. harness run about 500 to 800 bucks

 

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!