PeachParts Mercedes-Benz Forum - View Single Post

Rocketrider · #4 10-29-2008, 12:04 PM

I trust your expertise Brian, so I'll do exactly as you say. However, I'm curious as to which part of my original procedure is flawed. As I understand, the purpose of the VCV is to varibly bleed off vacuum between the supply and the modulator to the vent that runs into the cabin. As the VCV opens with RPM, cabin air should be sucked into the vent of the VCV thus creating a vacuum at the vent at that location. When connecting the MityVac to the vent port, I get no vacuum at any RPM. This may not be the best way to test the issue, but please let me know so that I can have a better understanding of the system.

Quote:

Originally Posted by Brian Carlton

Your entire testing procedure is flawed.

The first thing to do is to connect the Mityvac directly to the transmission modulator line. Pump it up and see if it holds vacuum. A slow bleed is fine..........say 15" in 15 seconds..........but, anything more requires attention at the modulator.

I did this first and if there is any bleed at all it is less than 15" in 15 seconds.

Then, disconnect supply vaccum from the T that is above the VCV and connect your mityvac to this port. You'll have the Mityvac on one side and the line to the modulator on the opposite side and the line down to the VCV on the bull of the T.

Pump up the Mityvac and get a reading. It should be somewhere between 10" and 15".

Now, gradually open the rack and watch the gauge. It should slowly fall as the rack is opened. You might need to pump up the Mityvac during the test if the modulator is leaking slightly. When the rack is fully open, you should not be able to pump up the Mityvac much at all..........very close to zero vacuum.

Ahh, I see! This way, I the car isn't running and I can open the rack completely.

That's a properly functioning VCV and it can be tuned to move the idle setpoint up or down depending on shift quality.

I'll be away for a few days and will see how you're doing when I return.