Rough RUnning C280 Wiring Harness

[suginami]

If you have a 93-95 C280 (not C220, C230), then your engine wiring harness is surely bad. The wiring harness goes all over your whole engine. When you see the part, it looks like a large octopus. The problem is the insulation they experimented with in 93-95 ends up degrading in the car due to heat, and the insulation turns to powder, flakes off all over. Looks like it's 2 million years old. If you're not getting spark to one cylinder, it's certainly either the coil wire or the spark plug wire for that cylinder or the next one. On these M104 engines, you have 3 coil wires and 3 spark plug wires. Each coil wire is responsible for 2 cylinders. What actually goes bad is not the wires itself, but the end of the wire or "boot". The resistance is in the boot, not the wire, just like Porsches and old VW's. The wires on these cars almost never go bad, just the boot. They are very sensitive to movement, especially if you pulled it out. Everytime you pull a wire, it's a good idea to put on new boots. They sell them at the dealer, and they're ridiculously cheap, less that a dollar each if I recall. If you do decide to change the wires (why? I don't know), only buy them at the dealer. They're around $200 which is a lot, but they are solid copper and worth it. Aftermarket wires are a silicon / copper blend and not nearly as good. Also, make sure you are running original Bosch copper core plugs. These engines are not made to run on Platinum plugs. If a technician sees them in your car, he will not diagnose it unless you have proper plugs installed. Go with the original, cheap copper core plugs, and change them every 30,000 miles.

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[mbesquimalt]

My car is a 1995 c280 manufactured August 1995 it has the 4 seperate fan speed buttons. I bought the car a year ago. One day this year it started running very rough almost dieing at stop lights. The check engine light came on. I limped home and turned the car off and back on the rough running disapeared. I took it to the dealer who said the engine code was for cylinder # 6 and was going to change coil the but had to order it in. When the coil came in I replaced it. It didnot fix the problem so I changed the spark plugs with bosch copper ones. Didnot solve problems so checked continunity of wires to the three coil from the conecter on the center module(good). I then used a 1000 volt meggger to check for shorts all three were greater than 1 gig ohm (very good) The six spark plug leads also are good. The reason I only checked one cylinder with my timing light is because you have to put it in line with the spark plug very hard to do. I think more than 1 cylinder is missing.
Back to the wiring harness. How do you tell if it has been replaced. My harness is wrapped with cloth similar to friction tape but not real sticky. I seen no signs of cracking where the wires are not wrapped. Also does anybody know if the repair cd shows all the conectors and wires in the harness.
I appreciate the feedback so far thank you.

[suginami]

Well, in my case, I carefully with a utility knife slit open a portion of the black fabric tape to inspect the wires. The insulation on the wires looked brand new, you could see the different colors of the wires, so I knew I was in good shape. I also had a vehicle master inquiry for my car ran at the local dealer, and it showed that indeed my harness was replaced at 107,000 miles.

I've since seen several harnesses that were removed from different Mercedes at my local independent mechanic, and it is very obvious. In some cases, the insulation had turned to powder, was whitish-gray in color, and just had disintegrated. In other cases, it was sort of flaking off, and you could see the bare copper wires exposed all over.

Symptoms of a bad wiring harness sound like what you're experiencing. From postings on these Mercedes Forums, you may experience any of the following: random and arbitrary engine fault codes, check engine light that comes on for no reason, rough running, poor idleing, missing, back-firing through the intake manifold, various shorts, frying of the EZL, EHA, throttle actuator, etc. I've read posts from owners who were beside themselves with thousands of dollars of repairs needed because a bad wiring harness took out other components. The throttle actuator costs a little over $1,000, for example.

I'm not trying to scare you, but I wouldn't let it go. It might be worthwhile to get it inspected by a dealer or local independent MB mechanic.

[mbesquimalt]

Well this is not looking good. We were very happy when we got the car last year it only had 55,000 miles. I don't like repairing or replacing wiring harness at work but I will be inspecting mine very caefully for deteriating insulation. Does the shop cd have a detailed wiring diagram. Thank you

[suginami]

The shop cd may have a detailed wiring diagram, but I don't have one. I've seen them for sale on e-bay, for what it's worth.

Go to a dealer and ask to get a Vehicle Master Inquiry run on your car. This will tell you what repairs have been performed on your under warranty or recall. These are the only records that the dealer will give you. You will also probably want or expect to get any records of regular service or maintenance, but they will tell you that these kinds of records stay with the owner, not the vehicle.

If the harness was replaced by the dealer, it will show up.

As a guideline, the harness will run you about $550, and an honest independent Mercedes mechanic can install one in about 3 hours. So you're looking at about approx. $800 installed if you have to do it.

I've seen pictures posted on other sites of what a bad harness looks like, where you can check to see if your harness is bad or not, and also stories of what happened to people's cars when it did go out.

I'll search for these and post them for you.

[suginami]

I'll continue to add threads to this post as I find them. Check back for future edits:

http://www.mercedesshop.com/shopforu...wiring+harness

http://www.mercedesshop.com/shopforu...wiring+harness

http://www.mercedesshop.com/shopforu...wiring+harness

http://www.mercedesshop.com/shopforu...wiring+harness

http://www.mercedesshop.com/shopforu...wiring+harness

http://www.mercedesshop.com/shopforu...wiring+harness

[suginami]

Here's more:

http://www.mercedesshop.com/shopforu...wiring+harness

[suginami]

Here's one that talks about a problem like yours and mentions how to check the resistor ends:

http://www.mercedesshop.com/shopforu...wiring+harness

[suginami]

http://www.mercedesshop.com/shopforu...wiring+harness

[benzboiinky]

my 95 c280 with 233k miles bought it new is misfiring bad to the point of it will die on me i have replaced the plugs plug wires and engine wirring harness coasting about $1200 bucks plus labor and still hasnt fixed my problems i have ordered the coil packs all 3 but havent receved the yet. if any one know or had somewhat the same problem pleaz let me know all u can about how you fixed yours thankz