What is the purpose of the vaccum valve to the rear of the injector pump?
It has two vaccum lines going to it, how do you check it?

John
84 300D 233,000

That vacuum box is your shut-off valve,if you apply vacuum injection pump will shut of fuel then engine will turn off.

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MB STARS Master Guild Technician,17 years MB tech
14 years independent shop owner

The plastic valve on the top rear of the IP (with two vacuum lines) provides vacuum to the transmission shift modulator. The shut-off actuator (metal cylinder) has one vacuum line, and is located on the rear of the IP, just forward of the oil filter cannister. If your transmission shifts smoothly, and your engine shuts off when the key is turned off, you probably don't need to check anything.