My 1983 300CD runs fine, but it does not seem to have any trubo boost anymore. When I bought it a year ago, it felt kind of "turbo" sometimes.
Perhaps my use of vegetable oil fuel blends has something to do with it.
Any suggestions? Maybe there is some switch or someting that is not activating?

Mark

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1983 300CD 245K
Running WVO blends

clean the banjo bolts and adjust the alda, also inspect the turbo for shaft play and ease of spin. could also be fuel filter issues, running blends can fog up the filters with a wax if you blend vegetable oil and diesel, which is also bad for the IP.so ive heard

As Don mentioned, the usual culprit is a clogged banjo bolt on the back of the manifold or clogged lines to and from the overboost protection valve on the firewall or a clogged overboost valve itself.

Get a boost gauge and T it into the line from the overboost valve to the ALDA. Take the vehicle for a drive and see what the gauge reads at maximum power above 3K. Then you'll know if you have an actual problem or not.

Start reading - it's an easy fix you can do yourself.

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- Brian


1989 500SEL Euro
1966 250SE Cabriolet
1958 BMW Isetta 600

the usual culprit is a clogged banjo bolt on the back of the manifold or clogged lines to and from the overboost protection valve on the firewall or a clogged overboost valve itself.

Please point me in the right direction:
What manifold are we talking about: intake manifold? exhaust manifold? IP? fuel filter?

Well, I guess the overboost protection valve is located on the firewall (back wall of engine compartment)

I love these cars with easy fixes you can do yourself!

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1983 300CD 245K
Running WVO blends

Here you go:

http://dieselgiant.com/mercedesaldaboostsystemservi.htm

If you remove the air cleaner housing, there is a black wire with a black plastic adapter plugged into a sensor of some sort. I was told that this is part of the overboost control system. Is this right?

Does the little switchover on the firewall check the pressure itself, and vent the overage, or is that sensor on the top of the intake manifold part of the equation? If not, what the heck is it?

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1982 300CD Petrol/Black Leather

The electrical connection to the overboost protection solenoid in the firewall originates at the intake manifold pressure sensor on top of the intake manifold. When the pressure sensor senses close to 16psi an electrical signal from the sensor switches the overboost protection solenoid, thereby cutting off the pressure signal from the turbo/intake manifold coming through the clear plastic line. This protection is in addition to the wastegate function and serves as a redundant safety provision to guard against piston melting and other such bad stuff when the turbo overboosts and EGTs go up to the danger level. However, since the IP has to be cranked up to get any more performance out of the engine, I don't see how a stock IP can overfuel and melt engine components in an overboost situation. Essentially the IP is governed so to speak. Overboost by itself can't hurt, it's overboost coupled with overfueling without adequate charge air cooling allowing EGTs to go up and out of range that causes the destruction.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)