juppzupp

Recently my W124 is giving me some trouble starting up and it seems to be related to the vacuum system.

Sometimes when I try to start it, it cranks over but does not start. (No smell of gasoline either)
Now the wired part: I look and unlock the car using the central loking system, and it "fixes" it! It starts right up after the first turnover.
Then I shut if off and sometimes i can start it again and sometimes it wont start. I use "the door lock trick" again and it fires right up.
Another observation I made is that if I dont wait for the vacuum pump to complete its cycle before i try to start it, it will not fix the issue.
Also just locking/unlocking the car without the central locking will not fix the issue!?

Once the car is running there is no issue.

I startet to look at the engine compartment while having the igniton on and noticed that in cases when it would start, I can hear the main injector pump (or at least something in that area) high pitch humming sound.
When it wont start I cant hear that sound. I am sure there could be a lot of reasons why it is sometimes not running but is there anything related to vacuum that could cause this?
or is there maybe some security feature (relay) that prevents the pump from running until unlocked?

I would really appreciate any advice since or more insight of how this engine works.

Thanks

stormtigers

Question -
Are you sure you don't have an immobiliser fitted ?
I have aftermarket one fitted and it is located next to the vacuum pump and triggered by the locking feature.

Otherwise - pull rear seat out and check out the vacuum pump.
Early in the piece with my car I had similar issues.
It turned out to be some very stretched rubber hoses that connect internally in the pump to the harder plastic vacuum lines that run throughout the car.
The rubber hoses are only a couple of inches long and resemble the rubber you see connecting gas lines to bunsen burners in the laboratory. Couple dollars to replace (do it even if they aren't your problem I would advise).
The fact that the central locking seems to repair the ignition issue sounds very much like the pump is not holding pressure causing issues. Once you activate it with internal locking it is recharging with pressure.

juppzupp

Thanks for your repsonse.
Not sure if I have an immobiliser. Bought the car a few years ago. Is there a way for me to find that out?

Anyways, I will definitely take a look at the vacuum pump. So it sounds like the vacuum system is somehow connected/related to the ignition? very interesting...

juppzupp

Haven’t quite made it to the vacuum pump under the seat yet but….
I started to take a closer look (or better listen) to the vacuum components and noticed that in the driver’s door I can hear a hissing sound when I look the door over central looking.
Took the panel off and sure enough it comes right from the vacuum element. Also noticed that the pump runs quite a bit after all doors are locked 20+ seconds (assuming because of the leak)

Could this be the cause for my starting problem?

If so, does anybody know what switch or element senses the vacuum and where it is? And the in return prevents the injector pump from running at start-up?

Again, any advice is very much appreciated. I am trying to get familiar with this vacuum/electrical system here….