Ok I have the problem figured out I think.

Can someone tell me if I understand the system correctly…..

Ok the pressure switch boost air pipe trigger switch in picture number 20.

When boost hits 15 PSI the switch grounds the switch over valve picture # 21

This in turn cuts the pressure to the ALDA picture # 14 and stops sending extra fuel to the pump.
If this is all correct, I have a bad pressure switch boost air pipe trigger switch in picture number 20 because when engine is shut off it is still grounded at the post….

I pulled all that crap off and have a manual waste gate regulator. No ALDA, no cutout solenoid, no nothing but a boost gauge. Disabled EGR and ARV also. Its a new car and lots more power. Been driving it that way for 2 years now and keep falling in love with it all over again every time I drive it.

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Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi

Oh also the 2 wires coming from the b terminal are ground triggers. One to the pressure switch boost air and the other to the transmission. ?????

IMO, for your application keeping it stock is not a wise decision.

A modern boost control is superior to 30+ year old technology and used components.

The MB system (if it is working correctly) should not activate below 11.9 PSI.
Today, many owners are lucky to get 5 - 7 PSI with the over boost protection bypassed.

FYI: Any leak at the exhaust/intake and/or turbo flange gasket wastes power = degrades performance.
Exhaust leak between engine and Turbo OM617

The MB OM617 over boost protection system was designed in the early/mid 1970's, while they developed the W116 300SD.


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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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just one more thought on over boost protection, is it really needed?

I don;t think so, the turbo will have a hard time getting much past 12 psi with the factory settings in the ip. I have also heard that at about 40 psi, and of course enough fuel to push it that far, as well as a turbo that can do it, is about where rods start bending, so you are well safe from that.

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1977 240D turbo

I replaced the over boost switch on the intake all is good now. I can cruse at 80-85 ho problem.

The five speed transmision is working out pretty well ratio wise it seems. No matter whose it is.

I think 4.88 vrs the 4.10 stock gears with the 33" tires I have on now would be better. But I only have the 33" tires on in the sumer. And back to stock size for plowing snow in the winter. 225/75/15.

Well I did so good for the first 200-250 miles but I could not drive like and old man anymore.
This last tank 26.6 MPG keep in mind I have 33x14.5x15 trusx tires and stock 4.10s

I am curious at what I will get with my plowing tires 234/75/15

The first half tank via the fuel gauge was 240. Before it hit the half tank mark

that's quite tall; i think the most common of the MB diffs is 3.07.

PS - i guess the huge tires make up the difference?

The first 617.950 engines had less power then the later ones.
If you have one of this early engines you could gain 10 HP by changing the camshaft.
You also need the cam towers, rocker arms and valve springs from the later model.
The # on the back of the old cam is 00 or 01.
The newer cams are 05 or 11.

X2 on removing the ALDA.

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76 240 D. Bought in 1998 for $25.
85 300D. Got it for free with a bad engine. ( Sold )
60 Unimog 404. What was left of it, was given to me. Now powerd by 617A.
88 560 SEL. Bought without engine and trans. Now powerd by 617A.
67 250 SE. Cuope. For resto or sale.
64 220SE. For resto.