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Old 01-01-2010, 10:07 PM
JimSmith JimSmith is offline
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,596
Originally Posted by Dovetail View Post
Hello all:
I have a 1980 300SD with 210,000 on it. It was previously owned by my cousin (since 1982), and was his daily driver until about 10 years ago. He meticulously cared for it up until that point, however his mechanic, although a popular independent mechanic in the Pasadena, CA area, is not someone who I would take my car to. They used 20/50 wt Pennzoil, which was regularly changed. Over the last 10 years this has been his second car, and approximately 10,000 miles were put on it over that time period, as well as run on homemade biodiesel (made by his mechanic). The maintenance was benign neglect. His wife started it oneday and it went into runaway (not traveling, but while in park). She had to call the fire dept who stopped it by blocking the turbo intake. After that the car was gladly given to me. His mechanic thought it was the fuel injector pump (stuck fuel rail), and had it partially dismantled. I found a good used injector pump, swapped it out, and got the car running. 6 degrees of off timing was noted so I rolled a new chain in. It now runs very nicely, however has a loud knock when cold (always had this), and despite new injector nozzles, still has the knock which goes away when warm. However, the most obnoxious thing is that it smokes really bad, and has significant blow-by. It is a little slower than other turbo diesels I have had, but still has respectable off the line speed and power under load (when warm). Before I put any more effort into this I figured I should check the compression. The readings I got were:


So the question is, is the 4 bar difference significant? Could that be the origin of the smoking grayish exhaust? The blow-by? By the way, despite several tanks of diesel the exhaust still smells like McDonalds. Do you think more time and money should be invested? I am thinking I will see if new valve stem seals will help, but I hate to invest much in it if I can not get rid of the smokey exhaust. Any comments would be appreciated,
Well, the compression numbers overall are very good, given the engine has less than a 20:1 compression ratio. And the high to low difference is over the 10% limit considered ok - meaning not to worry about - but the basic numbers are pretty high, so I don't think the difference is that telling. I don't think it is the primary cause of your smoking issues.

I think you need to understand why the engine ran away. I have never owned a turbo of that era and have not had to get to know the boost control system intimately. But, I have never heard of one of them or a 240D going into a runaway condition all on its own because the injection pump suddenly got unruly. I think someone was fooling with the shut-off or the Alda or some other boost control/fuel mixture sensing or feedback line to fix a performance problem. The new injection pump may be set up better, but it may still be suffering from bum control system sensors or calibration.

Given those compression numbers your smoking issues sound like a fueling system being out of calibration or an intake obstruction more than a cylinder to piston ring problem. Blow-by can be a result of the turbocharger bearing area being pressurized and then allowing some air to be pumped into the oil sump. Check general oil consumption rates. If you are getting 2k miles to a quart of engine oil, I don't think you have a an engine oil smoking problem.

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

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)
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