cpr_metro

Hmmmm
I had the entire liner on the left side of trunk removed and did
not see it. No sign of airlines that lead to it either. I think the airlines are clear plastic tubes. I can see the tube when I look into the trunk latch. Only thing there is the power antenna and cellular phone ( amplifier ) connected to antenna.

Dual 5Ls

Isn't it in the left side of the truck behind a panel, but encased in some type of foam?

SNIPE: I see we have similar taste in cars Are you on the Rennlist?

Peter Guenther

The close assist pump sits over the rear wheel next to the gas tank, It can be gotten to by removing the wheel liner (inside the trunk) but there is better access by removing the gastank liner which also covers the bottom of the rear shelf. Pretty straight forward pull the pins, remove the rivets. It takes a little more time if you have a CD, the radio tuner, BOSE Amp also reside in there. You will probably have to visit the area when the BOSE "goes" bad think scratchy speakers. I dont know who is rebuilding them these days but George Murphy might. The door locking, vacum headrests in the back seat(if ya got them), lumbars, backup rods, and vacum assist for the HVAC system are controlled by a similar pump under the passenger rear seat in a foam enclosure. In a later mod the trunk handle was moved from that pump to the close asist.

wwalston

I also have reset the unit in the trunk by pulling and reinserting the fuse. That cures the problem for a period but the period gets shorter and shroter finally its days not months. I pulled the vacuum unit and replaced it ...its good for a year or two. The unit that was pulled out has a good vacuum pump and the relays appear fine so the problem is in the electronics somewhere in my case.

s_nik

its the capacitors...

can we not just unsolder all capacitors and buy replacements and solder back in?

cpr_metro

I finally found the pump in my S500 Coupe...... its NOT in the trunk. Its under the rear passenger side seat under some foam rubber. YES...... the problem is not the pump itself it is the electronics. The same pump is used for the power door lock and my door lock works FINE all the time. According to George,
these pumps all have the same issue and Mercedes does not make that exact pump anymore. They have some universal pump with a retrofit kit for a given model.

As far as the capacitor go on the PCB.... we had the pump open and all the caps are surface mount type and they appear to be OK. There are no big electrolytic caps that I was looking for.
It might appear to be a capacitor problem....but I am not sure now. More than likely its a pre-planted bug in the micro-controllers firmware that goes into action X number of years after car is built. Planned obsolsense and sure fire parts sales.


Who needs power assisted doors and trunk anyway !!!!!
I just wish my Damn trunk lid would close flush with the car body.

s_nik

it will... just open the trunk look from inside (behind your licence plate) there are 2 levers... one is for the little latch and the other one is for manual closing of the trunk lid in case of a failure... looks like they were infact anticipating a failure and built in that feature.

OK I HAVE ANOTHER IDEA, EVERYONE HEAR ME OUT AND TELL ME WHAT YOU THINK

what if we install a relay in place of fuse #9 in a way that everytime car is powered up, this relay would cut the power to that fuse #9 for a few seconds... in a way its like resetting the pump everytime car is started so when you shut off the car and close the door pump will work...and next time you start the car, it resets, and so on and on... you get the point... this way we dont have to pop up the trunk and have to reset the fuse manually everytime. I spoke to a friend of mine who is a 4th year electronic's engineering student and he said it would be a breeze to build a circuit board accomodating a relay for something like this.... so whats the hold up? beats the $300 for a pump in my opinion.

barry S320V

Cpr:
When my trunk didn't close flush with the body I asked for help, and was advised to check the latch. This is the bottom latch that is attached to the body, not the one on the trunk lid. I took off the plastic trim on the lip of the trunk to get at the lower latch. Sure enough it was loose. A torq socket fixed the problem, nice and even closing. Total repair time about 15 min.

Barry

cpr_metro

Hi S_NIK

Yes..I am aware of the lever in the hood to facilitate the closing of the trunk. Tried it....and it does not help at all. I will look into the issue that BARRY raised about the lower latch. I think that is the problem.

Regarding the relay issue... yes in theory it should work, but it will bring varied levels of success since the "time to failure" I don't
think is the same for everyone.

ALSO....... my SRS warning light came on.... I am not sure when this happened.... BUT I think it coincided with me pulling the vacuum pump. Guess it makes sense. I will have it reset and see if it is a false alarm or not. Which someone would come out with a simple master reset button to clear codes for CK Engine Light and SRS Light.

Davetruong

Do you hear a clicking noise in your car while running? How does the car start-up?

I believe the situation is the central locking unit behind the seat. I too had the same EXACT problem. If replaced with a Bosch unit, it should cost about $350 from Phil at www.mercedesshop.com. otherwise it would cost $900 from MBZ. The reason why mine died was because there was a small leak, and the pump worked overtime, causing it to overheat consequently dying on me.

Best of luck to you

rhgtara

Davetruong: Did the pump you replaced have modifications???
from 15 vacuum lines all merged into 6 on the pump.

Davetruong

The pump did not have modifications, nor did it require moding. MBZ replaced the pumps in 1994 and retrofitted them starting 1995. If you had a 1994 or older, you might have to retrofit...Let me know if you need additional help...

rhgtara

Hi: I just replaced mine and had to do the modification. Did it
and all is working well. Thanks

Peter Guenther

There are two pumps, one for locking and other vacum needs, it sits under the rear seat in a foam rubber holder. the other is next to the gas tank over the rear wheel, this pump controls the closing assist (pulls in doors and trunk lid) and fails more often than the locking pump. The handle is controlled by the locking pump unless the suggested mod is made then it is driven off the closing pump. I am on my second, and took the first one apart to "see what it in there" well, I went to electronics school, and unless you have circuit layout you are out of luck.
The basic operation is a electrical signal from the doors or trunk causes the pump to run, the output is channeld via a little air relays. The pump runs untill it sees pressure or vacum or times out if it does not. I dont know where this capacitor story comes from, it could be so. There are major electrolitic capacitor problems in the Becker/Bose amps, these caps dry out and cause distorted or garbled sound.
There are people rebuilding all of these, George Barrett is doing the vacum pumps, and Becker is back in the business of doing the radio amps/tuners which also can have bad capacitors.
I speak from experience, having direct knowledge of these issues on my 92 SEL, among other problems

cpr_metro

The pulled out the PCB in my pump looking for the caps.
These are small SMT type... not the typical big through hole typer that I am used to seeing. Actually....are pretty hard to indentify.

NOW....that I have fooled with my pump my SRS light is ON.
Got a feeling its related to pullingh the pump.....maybe????
Have not checked it out with diagnostic computewr yet

jpcdmd

I dont own a benz but i just read on another forum earlier today about how to fix this problem. I think it was on mbnz.com. One guy said if you take the pump apart there should be an adjustable screw on or near the hoses (?) that should be turned a half turn or so. After turning the screw, check the distance that the doors close, if they close too much then the screw was turned too far, if they don't close enough or not at all, then the screw needs to be rotated the opposite way. Apparently the screw had something to do with the air transfer and the effect of the pump on the doors. It sounded like a solution, might need to do some digging on the other sites.

jpcdmd

I found it, its on mbnz.org............

Theres a pressure switch inside the pump that has the adjustable screw, check it out.

ataie

the vacuum on doors works only on one door. That's fine since The doors close fine. The problem is the trunk. When I close it the handle moves in, you hear a sound like something is clicking/grabbing, but the lid doesn't go down.

Is there a way to fix this WITHOUT changing the vacuum pump? I've already done the fuse thing and it didn't help.

thanks for your assistance,
98 S420

xrobk818x

THESE CARS HAVE THAT ISSUE TRY THE FUSES IN THE TRUNK REMOVE THE ONE FOR THE DOORS AND THE TRUNK THEN TURN ON IGNITION AND OFF AGAIN AND TRY IT IF NOT TRY AGAIN THEN IF NOT AGAIN THEN YOU NEED NEW PUMPS