I have a 2002 Clk 430 and as I was driving down the road the engine light came on and the car abruptly started running horrible. I could immediately tell I lost a cylinder. I had the codes checked and I have a random missfire code and a missfire on cylinder one. I tried swapping the coils from one to two and that did not work. Still says cylinder one. I then changed the spark plugs in cylinder one.... no change. I swapped fuel injectors on one and two....still says cylinder one missfire. I have read on other models that there is a notorious problem with a wiring harness....is this true for the clk 430 as well. I went by a muffler shop and they said they were pretty sure it wasnt the cats. I had the crank shaft sensor replaced last month when the car would abrubtly die when it got warm. Is there anything else I can do to check before I go pay mercedes two or three hundred dollars to diagnose. Any advise would be greatly appreciated. This has been very frustrating. I guess I should try swapping plug wires from one to two and have the codes rechecked but short of that just wondering if I could check anything else obvious before giving the car up for another week to the dealership. One of the guys there said the fuel injector could have gone off line and I have a bad computer.....anyone heard of this. I feel it is something simple because of the way it happened...It was like a light switch.....not a progressing thing.

 

Coil wires are much more common than the coils going bad.

 

You are on the right lines but need to be thorough.

IF the misfire is just on No1 then the something on Cyl. 1 is causing the problem. Pretty obvious but this is the starting point.
IF this problem is on several cylinders than it could be lots of other things. Just one bank of cylinders or both?

So what needs to be swapped / checked.

Plug / lead / coil / injector are all interchangable No1. to No.2.
If this makes no difference and code REMAINS on No. 1 AFTER an engine computer RESET / CXLEAR then need to look a little further.

Was the plug from No.1 a different colour to the other plugs?
What is the compression on No.1 vs the others?
What was the car doing when it lost No. 1. High speed? Could have burnt a valve but unlikely and the compression test will show this up.
What gas are you using?

Now this is the point it gets more difficult and potentially expensive.

Has the car been serviced recently?
Could some foreign body to have found its way to and blocked No.1 inlet track? Very unlikely BUT you never know.


Yes it could be the wiring harness. All you need to do is to inspect the wiring CAREFULLY (especially under clipping etc. for failed insulation. (in part due to high under bonnet temps on V8/V12 combined with high ambient)
So could it be the computer? Mmm. A few "desperate" ideas.

Could try measuring the voltage across the injector terminals whilst running to see if any obvious difference exists between No1 and the other cylinders. This will be a high frequency signal and the reading will therefore be "erroneous" BUT a difference MAY show up.
Never done it (SO DOING SO IS AT YOUR RISK) but it worth reversing the injector connectors for No.1 and 2.
Injection is sequential and although injecting at the wrong moment is not ideal it is better than not injecting at all should the signal from the computer have gone down for some reason.

Something makes me wonder whether in fact you cleared the DTC's before making your component swaps.
I'm surprised that you still have a No.1 misfire after swapping the plug, lead and coil!

Chances of the engine computer going down are VERY small But possible.. Mileage, age etc?

If all the above fails suggest you get the dealeer to do a STAR diagnostics Quick Check (MB equipment) and provide you with a printed report BUT do not procede further until you are in possession of this document. (Small charge. Agree cost upfront)

Good luck.

Stuart

 

You cannot check injector voltage. When misfire is detected the effected cylinders' injector is shutoff. As soon as you try to check the voltage the injector pulse will be killed. Swapping injector wires is not an effective test because they will fire in the wrong order-YOU should know this!!!!