PeachParts Mercedes-Benz Forum - View Single Post - Vacuum Problems

mach4 · #15 10-12-2013, 03:23 PM

Thanks for all the suggestions and ideas.

I pulled the check valve on the vacuum pump and it was good. It looked clean but I gave it a good cleaning anyway.

Tested the VCV on the IP and it was fine.

Tested the transmission modulator and it was fine.

I tested the vacuum shutoff solenoid for leaks and it was fine.

I then rechecked the vacuum at the rear port on the main vacuum line tap and it showed 8 in-hg.

I then plugged the one line that provides vacuum to all the chassis components and re-checked the vacuum as before and it went from 8 to 22 in-hg.

So while I don't have the problem solved, I know it's not in the engine bay.

The thing that threw me off was that since the vacuum locks continued to work after the engine was off, I assumed that I had no vacuum leaks in the chassis. Bad assumption. But the fact that the locks continued to work for the 4-5 cycles does seem to eliminate those from the equation.

Now the symptoms begin to make sense. The one time that the engine failed to shutdown altogether, was the one time that we were using heat on the trip. In fact it is the first time I had the heater on since probably May. So I'll start looking in areas of the climate control components for the leak first. Whunter and Delivery valve called it - thanks.

So first point of troubleshooting the chassis vacuum was to hook up a vacuum tap at the point where the chassis gets its vacuum from the VP. I drove it around with the gauge registering 6 in-hg in the off position. Moving it to other positions did nothing except defrost, where the reading went to 10 in-hg. Not sure what that means but it's a start.