As some of you may remember, I posted on this topic a while back. I still have the same problem - after the car is parked for 5 minutes, only the driver's door can be unlocked. (others must be unlocked manually.) But the plot thickens.

Problem #1 - When the car is running and I lock / unlock the doors, I hear a hissing noise from within the driver's door. All locks operate normally when the car is running.

Problem # 2 - After the car is locked and parked, the gas door will unlock itself after 10 minutes or so. Why this happens is beyond me. Thanks for any help.

Problem # 1 - not a problem. That's just the sound of vacuum venting from the filtered end of the master valve.

Problem # 2 - now you need to start plugging lines and find the leak. The fuel door lock should be at the end of the line, unless (and I don't remember) if the door is in the fender near the C pillar then it might not be at the end. Either way, cap off the vacuum line to that lock, there should only be one since the lock is spring loaded and vented to atmosphere (so if the vacuum bleeds off, the gas door will be unlocked). Install a vacuum gauge somewhere where you can keep an eye on it, run the engine or use a hand pump to build some vacuum and wait. If it holds, you found the leak, if not, disconnect and plug the trunk lock and repeat.

Continue the process of plugging lines until you hold vacuum 15 inches HG for 15 minutes, when you achieve this, you have isolated the leaking unit (keep in mind that one or more of the units already disconnected may also be bad). Once you get to the point you are holding vacuum, keep the last unit you tested isolated and reconnect one of the previous units. Check and see if the system still holds vacuum, repeat until all vacuum units have been tested and verified.

You might want to disconnect and plug the line that goes into the left fender, that should be heading to the vacuum resevoir. Taking the resevoir out of the system for testing will make even minor leaks very visible as the vacuum stored within the lines is nil. ALong the way expect to replace a few connectors between the vacuum units and the hard plastic tubing. This is just rubber hose vacuum line cut to make the connectors. I used 5/32" line, slightly smaller ID than the metric but makes for a nice tight union.

It takes a while to go through all of the lines, connectors and diaphragms, but in the end it's worth it.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

I guess my best bet is to use the Mityvac Vacuum Test kit? Anyone used one of these before? How well does it work?

Don't know about the MityVac, I have a Actron hand vacuum pump and a separate combination vacuum gauge/fuel pressure gauge. With the hand pump I can pull almost 25" HG in a few squeezes of the handle, and with the reservoir out of the loop, I can cycle the locks with a few pumps too. As long as the MityVac can pull about 15", I think it should be just fine.

I just thought of one other thing to check first. The check valve(s). Mine was going bad and would lose vacuum intermittently. I found that I could pull a vacuum on the valve, it would hold, but if I shook the valve the vacuum would bleed off. Changed the valve and then moved on to the rest of the system. On a gas engine the check valve should be between the intake and the first junction. On a diesel I guess it would be between the brake booster and the vacuum pump???.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.