Can someone explain/confirm the operation of the vacuum controls on the fuel injection pump? I can not seem to find method of operation details in the service manual, only testing procedures. I recently acquired an OM603 which I will be converted to drive a manual transmission . A portion of the vacuum control was already missing, but the vacuum stop, ALDA, and VCV are present.

As I understand it... it works something like this?:
1) ALDA - Intake manifold pressure is supplied to the ALDA via the engine overload protection solenoid Y30 (which is controlled by a manifold pressure switch). As the intake manifold pressure increases, the ALDA increase the fuel mixture at a given throttle position to compensate for the higher air density. If the manifold pressure increases beyond the pressure switch (roughly 1.1bar depending on engine), the solenoid switches dumping the ALDA input to atmosphere.

2) VCV - The vacuum amplifiers Y29/123 for the automatic transmission apply a vacuum signal to the VCV based on transmission shift profiles. When in gear and operating normally, full vacuum is applied to the VCV. If the automatic transmission wants to downshift, vacuum is decreased/more atmosphere is applied the the VCV causing the VCV to increase throttle position/increase engine speed to match the lower gear.

Is this right or do I have it wrong? As I figure it, converting to a manual, the ALDA should be good to go as is (my model does not have an interconnection to the vacuum switchover Y29). I think I should tee the VCV input to the vacuum line so full vacuum is always applied. Is there any reason to use the VCV for something else? Potentially using partial vacuum to increase throttle signal for AC/PTO operation?

Number 2 is wrong.

The VCV bleeds vacuum as the rack is pushed to full load position. It mimics a gas engine's vacuum profile. The blue flying saucer (vac amplifier) just dampens or makes shifts better in some way. I don't know exactly. It processes the signal from the VCV further to refine the shifting even more. The IP tells the trans what to do, not the other way around. The trans has 2 inputs from the engine and that's the vac signal from the BFS and the Bowden cable. The vac signal tells the trans what kind of load the engine is under so it can determine how hard and quick to make a shift, and the Bowden cable tells it where the accelerator pedal is in the range of travel. If you push the pedal just 1/4 of the way, the engine won't rev up much and the tranny sees a strong vac signal and a little Bowden movement. It shifts softly and early. Put the pedal through the floor and the tranny sees 0 vacuum and full Bowden movement. It holds the gear till redline and slams the shift as hard and quick as it can.

Hopefully that helps.

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Ah... OK, that makes sense. I found a similar post a bit later this evening, after a lot of searching, that explained basically the same thing. I guess the thrust control/pressure Bowden cable had me confused, I figured it told the transmission the engine throttle/pseudo-load position, while the VCV spoke in the opposite direction.

So I guess it will really do nothing when converted to a manual and I can't think of any way to use it at the moment. I really didn't want to remove it without having some way to cap the actuating hole in the pump, so I guess I can just leave it with both ports capped for now.

In general, the control pressure (Bowden) cable tells the transmission when/at what rpm to shift, the vacuum signal tells the transmission what shift quality to apply, shift quality being soft under low loads for a smoother shift and quick under high load to eliminate flare. The BFS integrates boost signal with VCV signal into the signal to the transmission modulator, and considers 50*C switch input to soften the first few shifts after a cold start.

The VCV drive shaft is sealed in the IP. It shouldn't leak or let in dirt because the VCV isn't attached.

Sixto
MB-less