R129 door locking vacuum pump

[Chris Taylor]

Coffin module is passenger side under the plastic cover in front of the windscreen - where the ECUs are hidden in a big metal box. From memory there are 3 screws holding the cover down. Bear in mind that's on my 93 500 so yours may be different.

That white tube from memory goes to the coffin module which also has vacuum supplied from a take off to the inlet manifold. It may be worth blanking that pipe off to verify no issues with the one way valve in the manifold drawing vacuum back via the inlet manifold.

Thanks.
I will have another look when I get the chance later.
That will be the same place as my diagnostic port.

 

[LostKiwi]

Thanks.
I will have another look when I get the chance later.
That will be the same place as my diagnostic port.

Yep that's the place - especially if you have the 36 pin round connector.

 

[Chris Taylor]

Yep I had a look earlier.
Mine is held down by 5 Allen bolts. One is stuck at the back beneath the grill at the bottom of the screen so to get into the box there will be a lot of stripping.
I did find the manifold you mentioned outside the box arc per photo so I need to work out which is the feed pipe to it.

 

[Chris Taylor]

Yep I had a look earlier.
Mine is held down by 5 Allen bolts. One is stuck at the back beneath the grill at the bottom of the screen so to get into the box there will be a lot of stripping.
I did find the manifold you mentioned outside the box arc per photo so I need to work out which is the feed pipe to it.

I guess it will be the white one at the bottom,
There is also a purple one at the bottom that you can’t see in the photo

 

[LostKiwi]

Yes the white one comes from the boot and there's another from the intake manifold.
Here's where they crack:

Fill the crack with araldite and they're good as new.

 

[Chris Taylor]

Yes the white one comes from the boot and there's another from the intake manifold.
Here's where they crack:
View attachment 59164
Fill the crack with araldite and they're good as new.

Excellent.
Mine has the start of a crack just there so I’ll Araldite it as you suggest.
It looked like a moulding mark but it’s exactly where yours has split.

 

[LostKiwi]

Excellent.
Mine has the start of a crack just there so I’ll Araldite it as you suggest.
It looked like a moulding mark but it’s exactly where yours has split.

That's not mine It's just a photo off the internet though mine did split exactly there. It's very common.
Don't put too much in - there are internal valves which can get gummed up if you're heavy handed.

 

[Chris Taylor]

I just smeared a bit over the crack and over the ball bearing.
Alas I still get the pump overrunning so I will have to see if I can check the pressure from the pump when locking to see what pressure it’s putting out. If that’s strong enough next step will be try to test pipes are all holding vacuum.
Any idea what the pump pressure should be reaching?

 

[LostKiwi]

I seem to recall 450mbar is the cut off pressure (7psi).

 

[Chris Taylor]

The pressure tester arrived today so I put it to good use.

All the pipes from the pump held solid and all the actuators worked. The only leak was the boot popper, but as the boot was open it wasn’t seated down. As soon as I pushed it down it held firm.

The pump doesn’t try to open all the locks at the same time. It does the doors together, followed by the glovebox and centre arm rest, then the fuel flap and last of all the boot lock.

I wondered if I should splice a T in the door lock pipe and connect the boot lock to the same line in the hopes it opens with the doors. Then doing that I’d have a spare outlet which would need an actuator on it to let the pump know it had done it’s job. I’d still be left with the pump over running to time out though.

I guess it looks like the pump is not sending air to all the locks at the same time. This will mean replacement pump time.

 

[LostKiwi]

The difference in timing will be down to a combination of resistance in the locks and deliberate sequencing of the locks by the pump.
On my own car the interior locks and fuel flap unlock after the doors. I can't remember when the boot unlocks but suspect on mine (93) it's the same time as the doors. I can't check at the moment as it's 500 miles away.

 

[Chris Taylor]

That’s taking social distancing pretty seriously..

 

[LostKiwi]

That’s taking social distancing pretty seriously..

It's hibernating somewhere warmer and drier...

 

[Chris Taylor]

Latest update.
I received a replacement pump from the US yesterday.
Unfortunately it behaves exactly the same as the old one over running and super slow unlocking the boot lock.

Does anyone know how the pumps receive the signal to unlock, could there be a control box causing the issue..? Would a Star diagnosis be likely to identify the problem?

The other option would be to T the boot lock pipe into the door lock pipe.. I wonder if that would work without causing bigger issues.

 

[LostKiwi]

Yours may be different but mine receives it from the IRCL module and is a single command to unlock everything.
Do you have s separate boot unlock button?

The pump runs until the switch off pressure or vacuum is reached. If it's continuing to run it's not reaching shut off.

 

[Chris Taylor]

Hi.
Yes I do have the extra button and pressing for boot only takes about 20 seconds.. I’ve usually given up by the time it opens. The thing is that both the boot lock and the popper circuits hold air as they should and the boot popper only receives a short burst about 5 seconds after the boot lock releases

 

[Chris Taylor]

At least I now have a spare pump even if I did have to pay over £120 for VAT and postage

 

[hop3]

Hi Lost Kiwi and Chris Taylor. I have just purchased a 98 SL2800 R129 that has central locking issues. It locks from the key fob, but will not unlock the car- but unlocks the boot only. The dashboard button will not activate the boot.
The car has had the original 1298001748 pump replaced, which fixed the problem originally.
So Im looking for some advice please. Would you recommend sourcing another pump to see if this fixes the issue, or is there other issues I should check first- like the cracks to the manifold? I did find a U-tube on using a vacuum/ pressure hand pump to check for leaks.
some guidance on typical costs and parts source would be most helpful too. Living in NZ.

 

[Chris Taylor]

Hi hop 3.

The vacuum tester was worth buying as it confirmed that all of my actuators and pipes were working fine.
Buying replacement pumps is a pretty expensive business and in my opinion risky.
It could be that you have the same issue that I had.
It turned out that my pump needed the two little cog wheels inside to be adjusted so the pump could run through its full cycle. If you open the pump you will see two cogs on a spindle attached to an actuator. The actuator moves in and out and operates a contact which reversed the pump.
I stripped this actuator out of the replacement pump and put it in mine. With a bit of fiddling and trial and error I adjusted the cogs and the original pump now works fine.
I did the same with the other pump and that now works too, other than the boot release for some reason..

I’ve attached a photo where you can see the little actuator.
If you wind both cogs in towards the contact in the middle it may solve the issue.

I used to leave the lid off and connect the pipes with it in the boot so I could watch it trying to work.

I hope this helps

 

[hop3]

thanks Chris.
I have found a crack in the vacuum manifold, and a fold in the white vacuum tube.
Im having a really difficult time though sweating the tube back on to the manifold nipple. Any tips on how to heat and expand the tube. Im trying heat from hot water, my wife's hair drier and hair straightener!