Car is a 1984 300td.
I don't have any quantitative numbers on the fuel economy, as I just got around to fixing my intermittent odometer, but it seems to be lower. This is accompanied by black smoke at idle. Not very much and worse on a cold start, but it didn't used to be there last week.
Only things that have really changed is I added some fuel lubricator to the tank, I can't remember the brand, but it was recommended on here somewhere....

4 days ago I had to adjust the rack damper in just a touch to kill a terrible vibration at idle. The engine starts perfectly fine when it's 20 degrees F outside, one glow cycle and it fires up like it was hot. The engine runs really smooth through the whole RPM range and has good power and NO blowby. The oil cap just sits on the cover not even moving when it's loose.

Only things that worry me.... Someone has removed the solenoid thing (overboost valve?) between the intake manifold and the ALDA and the ALDA is missing the little cover over the adjustment screw. Also the banjo bolts have been cleaned out. So I'm not sure what's going on there, had I known to look for that when I bought the car I may have walked... Anyway, any suggestions on where to go from here?

I should also note, yes it's diesel smoke. It doesn't smell like oil or coolant, definitely smells like diesel smoke. Part of being a good mechanic is knowing what different fluids smell like when burned out the exhaust or off a hot engine

Usually, diesel smoke is unburnt fuel. The two things that come to mind are valve adjustment and possible air restriction.

Also, are you in an area that has converted to #1 diesel for the winter months? This will give you reduced economy.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Yea, we do change to a different fuel mix in the winter. I don't think it's #1, they just add crap to it. Same thing happens with gas and gas mileage in cars takes a dump.

However, the smoke at idle thing is worrying me because I don't know why it's happening. I'll try pulling the air filter cover to see if it's causing a restriction and stops the smoke, but the filter is pretty new...

The previous owner said he just had the valves adjusted, but I guess it might make sense to check them. I should go buy some wrenches to bend into adjustment wrenches, no sense in taking the cover off and checking the adjustment without having the tools ready. Would badly adjusted valves cause smoke at idle, though?

Or is it possible to get crappy diesel from a station, my last fill up was out in the middle of nowhere at a tiny station. It's hard finding diesel in the boonies in Maine sometimes. We were camping out of a friend's truck a few years ago and had to buy some offroad diesel from a equipment operator...

The special bent wrenches are nice but not a necessity. I've done several valve adjustments on mine and still don't have a set.

Also, you may have the rack dampner a little tight. IIRC, there should be no perception of rpm increase at cold idle..

May need to replace the injectors....

Valve adjustment could be due...

EGR could be screwed up, not allowing enough fresh air into the intake...

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The car seems to idle the same when cold as when hot... Maybe I'll back the damper out some and see how it effects hot idle, I thought having it too tight would make the engine hard to start. I guess I don't fully understand how it works other than "it made the problem go away"...

Wrenches are cheap at horror freight, if it makes the job easier I may as well buy some and bend 'em up.

I wouldn't be surprised if the injectors needed to be rebuilt.... EGR is disconnected, so that shouldn't be an issue. No need for the engine to be sniffing its own farts

Well I backed the damper bolt out until it started to run bad, then turned it in a touch. I might have to replace that since adjustment has been a bit random and hard to nail down, it seems like a common issue. Filled the tank all the way up today and reset the trip meter, I have a lot of driving this weekend so I'll see how that goes.

I can't tell about smoke as it's windy now and there really wasn't much, just more than there has been, so ehhhh time will tell.

If you have the time why not run a can of diesel purge through it before the weekend driving should only take 1/2 hour.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Well this weekend I drove 384 miles, by the GPS. 100 of it was highway and the rest was bonnies of Maine back roads. So lots of heavy throttle up hills, speeding up and slowing down. 3 people in the car and probably 400lbs of stuff in the trunk. Not only is SLS the most amazing thing on the planet.... I got 27mpg. I guess I really can't complain there, my previous fill up wasn't at my regular station and may have been a bad grade of fuel.

As mentioned: Valve Adjustment, Fuel Injection Pump Timing and lastly Injectors. You could also adjust the ADLA.


The solenoid thing (overboost valve?) is was removed protects against the Turbo over boosting in a situation where the load is high. Like if you were pulling a Trailer up a steep hill.
When that happens the combustion gas pressure in the Cylinders shoots up and that intern turns the Turbo faster increasing the boost Pressure and the ADLA in theory is going to give you more Fuel due to the increased boost at time when the engine is sort of bogging down from the load.
Anyway the Valve reduces the Boost pressure which intern cuts back on the Fuel.

The official description is in the Mercedes Service Manual

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84 300D, 82 Volvo 244Gl Diesel

Should I worry about replacing it? I've read a lot of conflicting stuff about it, you don't need it, you do need it, blah blah. I might just install a boost gauge and keep an eye on it when I'm really pushing the pedal, then if I ever find a new overboost thingy at a junkyard I'll throw it on.

If someone posts one of those free sites where you can view the Service Manual you can read and decide.

Someone on this forum might sell one to you.

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84 300D, 82 Volvo 244Gl Diesel

One of the service manual sites...Setup like the CD's....


W123-dokumentacja cz. 2

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That's awesome, thanks!
The sound effects are really annoying, but free is free!