Why? Because this may restore reliable function to your closing assist pump, which may have stopped running making you think it was broken. Oh, and it may save you several hundred dollars for the cost of new one that you don't really need. I fixed my trunk closer recently as described in this post, but it stopped working this afternoon after about a week.
http://www.mbnz.org/forums/forums/th...id=13#M1284242
A couple months ago, I had taken the cover off the pump and noticed an electrical switch which looked like it may have been a pressure sensing shut-off switch, so I decided to look at it more closely, and in fact, it that's exactly what it is.
Pump operation explained. The pump does the closing of the doors and trunk with pressure. It pressurizes the lines causing the extension of pistons in actuators, which in turn move levers in the various latches, which pull the doors or trunk closed. The pump runs until one of two things happens: 1. It reaches a pre-set shut-off pressure (at which point the pump "thinks" it has properly done its job by fully extending the operational actuator piston), or 2. It never reaches its pre-set shut-off pressure and then runs for a set amount of time and turns off (that is, it "times out"). After pressurizing the line and doing the auto-closing, the pump then pulls a vacuum on the line, presumably to ensure retraction of the actuator piston. They are spring loaded, but I suppose they may not retract fully on occasion.
The problem arises in case 2. If the pump times-out twice on one line, then the electronics permanently shut off that function for the pump. Imagine that your trunk closer line develops a small leak preventing the pump from reaching its shut-off pressure. Eventually, the trunk closer line will shut down. Leak checking (it seems to me) is an important step if your pump repeatedly ceases to function.
If your pump stops working, you must electrically disconnect then reconnect it. Mine came back to life just fine. I had to disconnect the connector on the pump, however. Some say pulling fuse 9 in the trunk works, but it never did for me.
The pressure shut-off is a balancing act. You want to set the shut-off pressure high enough so that enough pressure is developed to latch the door or trunk, but you don't want it set too high so that the pump takes too long to reach the set pressure and times out.
I noticed that my doors and trunk would stay pulled closed for a while (many seconds after I had audibly heard the latch catching) before relaxing when the pump shut itself off. In other words, it seemed that the shut off pressure was set pretty high such that the pump kept pumping unnecessarily long after the door or trunk was latched. When my trunk stopped working again, I figured if I could turn down the shut-off pressure then that should restore reliable function. Time will tell if that is the truly the case.
So here is how to turn down your pump's shut-off pressure.
Pull out the pump and disconnect all the lines. Label them before disconnection if they aren't already. Unscrew 6 screws on the top of the pump and pry off the cover.
Admire the dual manifold design with solenoid switching between pressure and vacuum for each door and trunk line. Kinda cool. The pressure shut-off diaphragm is visible in this pic.
OK, here's the business end. Notice the dual contact switch that is operated by the white piston from the pressure sensing diaphragm. That white piston has a screw in the end of it which can be adjusted to adjust the shut-off pressure. If you screw it out a bit, then the piston will have to move less to trip the switch, therefore the pump will shut off at a lower threshold pressure.
Just turn the screw to adjust it. I just used needle nosed pliers. Finally, here's my original vs. new setting.
Now, my pump shuts down automatically in a lot less time after closing the doors and trunk. I think this is all that is needed to restore long term function. We'll see how this goes. I'll certainly report more if there is more to tell.
Brett
Linear Mode
