What in the world is this little valve for???
 

On my 83 300SD there is a small electronicly controled vaccum valve on the firewall above the injection pump - it's not hooked up but what is it for??? I can't find any loose lines and I will try to get a digital camera out here to take a few shots of it - any ideas??

Picture would help. Its worth a thousand words.

MVK

Probably the overboost connection, which has been disconneted and bypassed. A photo would help though.

It's definatley not the overboost valve - it better not be... I will try to get a picture as soon as I can for you guys

Pictures of valve:

Its the overload relief valve.

MVK

What is the overload relief valve for? Do you mean overboost valve? should I hook this sucker back up?

Yes it's the overboost switchover valve. It vents the ALDA to the atmosphere while disconnecting the signal from the intake, to kill fuel enrichment. You should hook it back up as long as it is not plugged, which may be why it was disconnected in the first place. If it's plugged you can replace it.

HTH,

ok I will run tests on this valve tommrow then - I dont like engine saftey features being bypassed! - thanks for your input - William

In my case, the valve was good but the switch on the intake manifold that actuates the valve was stuck. If you can blow air through the fittings of the valve when the engine's off or the electrical connector is removed, the valve is probably okay.

Sixto
91 300SE
87 300SDL
81 300SD (sold)

Everything checked out with the valve so it's back in operation