520i L-JETRONIC pressure switch. What does it do?

[heminglopez]

I have been trying to find out what the pressure switch 13621287760 purpose is, on my 520i  L-JETRONIC. 
Its does not do any difference when i unplug the connector, or remove the vaccum from the manifold.
Will someone please explain, thanks.
 

[Aldo525]

Not 100% sure but earlier M20 engine have a "gases emision control" system, see the link

https://www.bimmerforums.com/forum/show ... r-(M20B23)

 

[heminglopez]

Well it could be, its just weird that something like that is not mentioned at all anywere.
Its not a cheap part, so i was hoping it might do something

Thanks for the reply
 

[Federico]

This sheet from the service manual calls it a "partial load switch". Maybe you could test it by applying vaccum and checking for continuity changes.

 

This is clearly a BMW add on to the basic L-Jet, so the answers are probably in one of these tech bulletins:


 

 

[heminglopez]

Thank you, i havent seen that book before it might help me.
But i have no clue what a partial load switch is .
 

[Federico]

Thank you, i havent seen that book before it might help me.
But i have no clue what a partial load switch is .






 

 

 

 

 

My guess is that it switches at a certain vacuum spec to richen the mixture.
They probably had a lean cruise, a rich WOT and this switch operated in a part throttle/part load situation. (i.e. going up a grade, half throttle overtaking/acceleration, etc.)
But that's my guess. The pictured bulletin is from ebay; I don't have a copy to check.
BMW had class leading efficiency back then, so it makes sense they would tweak the ECU to run lean whenever the engine was crusing with high vacuum.