QuestionI did succeed in removing the vacuum/air pump - all still connected except the hose to the fuel filler door. As stated before, I can hear the motor run, and it changes pitch when switched from lock to unolock using a key or the IR fob.
When removing, the hose to the fuel filler door, so have a hose running from the unit. When the motor is running, I can detect no vacuum or pressure, either by finger over the end or holding the hose end in my mouth. I expect enough vacuum or pressure to operate the lock switches should be readily detectable at the pump hose.
My diagnosis is the the pump is not functioning, although I've not yet tried to track down any massive vacuum leak in the distribution system as you suggested. Would you recommend checking the pump unit for proper function before I proceed to seeking a possible vacuum leak in the hoses? Is the pump repairable or just replace it? Since it's not working now, I figure I may as well try disassembly to see if I can fix anything - nothing to lose!
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Followup To
Question -
Central locking system stopped working and now must manually lock doors and trunk, which doesn't lock gas lid, glove box etc.
Checked fused ok. Note that when I turn trunk lock key or press infrared button, some device in rear trunk sidewall under gas filler cap activates - changing operating sound when locking or unlocking, then stopping after about 10 seconds.
Based on what I've found so far on internet, assume this is a vacuum and air pump operating, when I press the lock or unlock mode, but no door lock/unlock is taking place.
Tried removing the device from its housing (shrouded in black foam rubber) but doesn't seem to be room to remove and didn't want to pull too hard and damage something. All wires/tubes seem to be properly attached.
Tried syncronizing locking system per owners manual instructions. Do not have shop manual or wiring diagrams.
Where do I go from here?
Answer -
R129 Roadster
Chassis 129.066
Engine 119.960 V8-dohc
Model 500SL
Years 1990-93
Answer:
Your issue is a massive vacuum leak.
Listen near each lock for a vacuum hissing.
The issue should be a broken hose/line and/or Vacuum Element.
You need the vacuum diagram for the car, and a hand vacuum pump for diagnosis.
mityvac, MB diesel owners hero.
http://www.mercedesshop.com/shopforum/showthread.php?t=102414
MB Tech Manuals from MBUSA cost $19.99 plus S&H
http://www.mercedesshop.com/shopforum/showthread.php?t=142445
Vehicle: 1991 Mercedes Benz 500SL
Part: Vacuum Element
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Vacuum Element
Door
Left : Right
When superseding from old part numbers 000 800 85 75 or 000 800 94 75, (1) 202 805 03 44 plug adapter and 50 mm of 007 997 61 82 vacuum hose are also required.
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Vacuum Element
fuel filler door
On 124 chassis models prior to chassis cut-off listed,when superseding from old part number 000 800 91 75, (1) 202 805 03 44 vacuum plug and 50 mm of 007 997 61 82 vacuum hose are also required.
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Vacuum Element
Fuel Filler Door
Chassis: F-112414-
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc
AnswerYes, remove the hoses from the pump, verify pump vacuum, then proceed to test each line with a hand vacuum pump.
mityvac, MB diesel owners hero.
http://www.mercedesshop.com/shopforum/showthread.php?t=102414
PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1991 Mercedes Benz 500SL
Part: Vacuum Supply Pump
Note: For Central Locking
Chassis: -F 097251
O4000-74540 Vacuum Supply Pump Hella IN STOCK $489.56
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=merc
