When I start my car it runs great...for about 30 seconds. Then it runs on 7 cylinders. I changed my engine harness because it was decomposed. I thought this was my main culprit. After changing it out, it still misfires. I started pulling spark plug wires until I got to #1. That is the problem. I switch the plug with #2 to see if it will change. #1 still misfires. I assume it's the wire, so I put a spark plug on it and it throws a nice blue spark about an inch! I checked the distributor cap, there appears to be snail trail on it. I clean it all up and lightly sand the brass on cap and rotor. It still misfires. Could it be a valve? I assume they are hydraulic. Why does it run good at any temperature for about 30-60 seconds and then misfire?
I would appreciate any help.

Hi Tidyman
You said you had a snail trail that you cleaned up? Often the trail is symptom of a microscopic crack that is shorting some high voltage to ground. When the plug is under compression it takes a lot more energy to fire the plug, than when you look at a test plug outside the engine. Another thing is to check the injector at the missing cylinder with a noid light, to make sure the signal is getting to the injector. It also could be a faulty injector failing when it warms up. The valves or lifters Would most likely fail on startup and then become better as it warms up.

Thank You Hal. I will look into the injector. Yesterday I switched the distributor caps from right to left to see if the misfire would change. It came back again, so the injector makes more sense.

There is an article in MBCA Star magazine that explains how current travels past the o-ring between the distributor cap and the "cover" which is held down by the rotor. When the o-ring is bad, the current goes to the rear of this cover.and can be seen by a trail on the back side of it.

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1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out

I'm sorry so slow in responding. That is an interesting phenomena that you are explaining cmcdonnell. What issue can I find that in so I can read further?
Here is the latest: I put Seafoam in the oil and the gas tank. Within a few miles of running on 7 cylinders, I put it in neutral, turned off the engine and turned it back on and it ran like a dream for the next 60 miles through hiway and city driving. Then it started again. I had the oil changed and it does it half and half. I filled my tank and put in another high quality fuel/injection cleaning treatment. Today I had only one incident of the misfiring and I drove about 60 miles through mostly hiway, and a lot of city too. I had my mechanic take a look with his analyzer and he came up with code 17. When this car runs good, it is awesome. If I am on the hiway and turn off the engine and then turn it back on and stay on the hiway speed, it always stays running good, especially if I'm running at warmer engine temperatures.
What do you think now?

I am on vacation right now, but as soon as I get home I will find it for you. The bulk of posts that have read concerning running problems on the M119 have consisted of ignition problems. When I bought the 400E about a year and a half ago, it ran terribly, especially when it warmed up. After changing the coils it ran better, the wires even better, the caps and rotors (which did not look bad to me) much better, indeed. Then I rebuilt the engine harness and it purrs at a stoplight. I'm still having trouble during the warm-up with what feels like running too rich.

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1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out

Thanks for your help. I will watch for that article.

what I do with bad injector is pull it out disasimble and clean the crud trapped by the screens.assemble it with clean gasoline,and put back in motor.Change fuel filter if alot of stuff in injector.If that fails I replace with new injector they can wear out

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Is it pretty strait forward on disassembling the injector? I can do most anything mechanical, however, I have noticed that a lot of modern things break when you go trying to disassembling.

Sorry for the delay- I was at the beach. The article I mentioned is in the MBCA Star magazine, Sept.-Oct. 2010. It is titled "Ignition Misfiring on 1990's Engines" by Ken Adams. If you are a MBCA member, you can pull up the article on the club's website. I don't want to publish it here because it does not belong to me. Generally, it says to remove the caps and rotors and inspect the insulating covers for tiny cracks and scratches which could be from spark passing through the covers to ground. Check front and back for evidence.

__________________
1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out

It turns out that its the spark plug wires. I switched the #1 wire with the #4 wire and my miss went to the #4 cylinder. Next I took off the spark plug covers and checked out the engine on a very dark night and noticed what looked like twinkling little stars all over the engine. No wonder it misfires. I ordered a pair of wires. I'll see how much better by this next weekend. They come from New York.
Mark