how is this checked...?

what is this?

what part number is it?

another user told me to check it out so i need something to start with?

It looks like this.

With no power, you should be able to blow through the lower fittings from one to the other. With power on, it blocks flow from one to the other (bottom) but vents one to the top (not sure which one). If air will pass from one to the other on the bottom, it will allow boost.

To find it, follow the vacuum line from the driver's side of the intake plenum, goes directly to the overboost solenoid valve.

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__________________

Gone to the dark side

- Jeff

I've put 60,000 miles on my CD, it has been bypassed.
Some folks will mention your world will come to an end, yet an MB mechanic says otherwise.

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83 SD

84 CD

An, single, one, solo, uno, ein.

Running with the overboost disabled is a poor choice unless you have a boost gauge installed and you actually look at it.

^^ I'm sure folks understand what the definition of an is. Maybe this mechanic is not interested in making his company money.
I have driven three 123's with it unplugged, my world has not ended. I do put my foot in it routinely.
Perhaps I'm lucky.
I do not have a boost gauge.
Is there any info on engines that have been destroyed because of this?

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83 SD

84 CD

I have a 300SD and a 300CD both with the over boost bypassed with no problems for many years. The max boost is set by the waste gate in the turbo, the over boost will not allow ALDA boost in lower gears. Helps transmission when starting out with a trailer or heavy load.

Thats the point of the overboost protection, if the wastegate fails there is nothing to save the engine from damage except an observant driver and the overboost protection system.

That applies only to the 78-79 model 300SD.

How to test it?

Have you tried babymog's test?

I'll look up what I can in the FSM, if you let us know what car.

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83 SD

84 CD

Remove the connector from the boost pressure switch on the intake manifold. Ground the connector; that should actuate the valve, which should block the input side and vent the output side.

1987 300sdl