Well, this is going to be a long post as I want to make sure I get the facts down, completely, so if anyone can help me, they will start from where the car is now.

A week or so ago I posted in the Tech forum, noting the car was not running on cylinder number one. This is relatively new as until about November I have driven the car since it was built in December 1985, and when I turned it over to my son then it had 200,000 miles or so and ran pretty good. I got a routine 23 to 26 mpg, depending on time of year, driving mix, and type of gas. This car never agreed with the EPA that MTBE was good stuff, or even a fuel. So, in areas where there is a low or no MTBE content, the car runs much better and can get up to 28 mpg on the highway.

So, Peter drove the car to school and back every day, which is about a 9 mile drive, for a few months. One day I happened to hear the car running poorly and asked him when it started running like that. One thing led to another and we were pulling plugs to see what was up.

First we pulled the number one plug connector with the engine running had no effect, so we pulled the plug out. It was covered in thick black stuff, and it was a Bosch Platinum 4 plug. The other three were a light tan color and also had a bit of black dust around the threaded end, away from the plug gaps. I also noted the spark, when the number one plug was out and then put in the connector and grounded against the intake manifold, was a kind of yellowish, thin "wimpy" spark. When I posted this Benzmac was good enough to reply that the spark plug connector could be bad and recommended I change it and the plugs to the Bosch copper units.

I ordered a distributor cap, rotor, plugs and plug connectors from Fastlane, and Peter installed all of it earlier in the week as I was on a business trip. While the car ran better, it was doing it on three cylinders. The spark still seemed wimpy to Peter. I posted this and another person took pity on me and suggested the plug wire might be bad.

I had Peter do a compression check at the highschool auto class and found some real bad news. The number one cylinder was getting 27 psi, while the rest of the cylinders were over 155 psi. So, when I got home on Thursday we popped the valve cover off and checked valve clearances. They were really bad. I have never done this job in this car before as you have to remove the camshafts to make any adjustments, and I was reluctant to do that when the car ran well. So I have had the local dealers do about 6 valve adustments over the life of the car (206,000 miles).

The number one cylinder, first intake and exhaust valves were hard up against the cam. The second intake and exhaust valves were about 0.050mm. The spec is 0.100 to 0.200 for the intakes and 0.250 to 0.350 for the exhausts with the engine cold.

None of the other cylinders had gaps in the spec range, and two other valves were less than half the minimum reading. Well, if the valves don't shut you don't get much compression, so I thought I had the problem figured out.

Last night we took the exhaust cam out, and hand ground the little shims or thrust plates as they are called in the manual, to get a cold clearance around 75% of the maximum cold number. When we got done, we were a little tight as the car this morning was ice cold and when we took the measurements it was too hot to leave your hand on for any lenth of time (over 40 degrees C). Some valves are at the minimum spec, but most are at least half way to the maximum number, ice cold.

We did the same to the intake valves, and got pretty similar results. The intake cam went back in a few hours ago, the engine was buttoned up, and the true test started with the engine.

The car fired right up but the idle was still very rough. Pulling the connector from the number one plug gave the same, no change, indication. As the car warmed up it seemed to run better, but still rough. I touched the number one exhaust manifold tube lightly and it was just as hot as the number two. This was while the engine was still barely warm to the touch.

When you tip into the throttle, the car revs now. It used to bog down and then rev up. Once it started showing some water temps, I took it out on a test ride about 20 miles up and down the highway. At higher rpm, like 3,000 and above, I cannot believe it is not running on all cylinders. The response is smooth and strong. If it is not running on all four under these conditions, then it is the best 3 cylinder in the world.

Now, when you pull the number one plug it has no detectable effect immediately, but when you put it back on it makes a loud pop, and the engine momentarily speeds up. The idle speed is as well controlled, even if it is rough, as it has ever been. In fact, when you came to a stop and put the clutch in it used to stall. Now it may drop to 900 rpm and then quickly holds at about 1000 or 1050.

Peter will do another compression test on Monday at the school, and I will report back. When we were checking the clearances under the camshaft lobes we were pushing the car in 4th gear. When we were done there seemed to be compression on all 4 cylinders, some a little better than others. By the way the original test Peter did showed the compression to be unaffected by repeating the procedure "wet" leading me to conclude the problem is in the head. The shop teacher had Peter take a sample of the coolant and look for exhaust gases, possibly to find if the head gasket is shot. No such findings. The coolant was free of exhaust and the oil is free of coolant, as the coolant is also free of oil.

I pulled the number one plug after the test drive and it was pretty clean. It has about 40 miles on it, and Peter noted after he first put it in and then pulled it, it was pretty black. Not so tonight, it was covered in a light coat of stuff that wiped off, and looked dark on the towel. I checked the spark, and it was much better than the original spark. I made an audible crackling sound and was blue, and moved around from event to event.

If you pull the number one plug connector the car is notably harder to start. Once started though putting it back on does little other than make a popping noise, and give a momentary surge in the rpm. After that the engine runs the same rough and lumpy way. If you pull the number two plug connector it makes a noticeable difference in rpm stability and roughness (gets a lot worse).

Well, I am at a loss for what to do next. I am tempted to go in deeper and take the head off. This is a pain in the rear on this car, as there is a lot of stuff not covered in my spotty MB manual. Taking the head off is a month job for me and Peter, as I travel a lot and he is just cutting his teeth on auto mechanics. Plus we have to find a suitable shop to have it rebuilt, if that is the problem.

Any suggestions, even for a suitable Mercedes shop to take it to for the head reconditioning, if that is what is next, will be greatly appreciated.

Thanks, and sorry for being so long winded. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)