fuel pump priming

[zaq123]

Any known reason why BMW designed it so the fuel pump won't prime unless the engine is turned over? Just want to understand the logic.. Flood clear in case an injector is leaking? Something else? Wondering if I should let Haltech prime it or work as stock setup.

[82eye]

i think the fuel rail retains enough pressure to feed the injectors initially on start. if the dme doesn't see a turning engine immediately after it shuts everything down as a safety factor.

[zaq123]

i think the fuel rail retains enough pressure to feed the injectors initially on start. if the dme doesn't see a turning engine immediately after it shuts everything down as a safety factor.

Im just trying to understand BMW logic behind that design.. So in 1989, BMW decided to go unsafe with M42 BMW and start priming? Or it was only due to DME limitations and m42 finally got the fuel prime when motronic 1.7 was introduced to e30?

[82eye]

Im just trying to understand BMW logic behind that design.. So in 1989, BMW decided to go unsafe with M42 BMW and start priming? Or it was only due to DME limitations and m42 finally got the fuel prime when motronic 1.7 was introduced to e30?

it was the e30 that is different. every other bmw of that era primes. partly it was due to early electronics.

edit: the e30 motronic is a super basic system.

[MrBurgundy]

Let it prime.

Every car that's injected should prime.

My guess as to why it was designed that way was because of the rudimentary DME functions at the time.

Having something run or not run is more simple than having a prime command and also a run command.

There is nothing that would be a weak point on the M20 fuel system if you allowed it to prime. It's a return style EFI. They designed 1000 cars that prime with the same style fuel system that all prime.

[zaq123]

it was the e30 that is different. every other bmw of that era primes. partly it was due to early electronics.

edit: the e30 motronic is a super basic system.

yeap, the only e30 that primes is m42 e30 which was like the end of e30 era. I guess Motronic 1.7 got more advanced ?

[82eye]

yeap, the only e30 that primes is m42 e30 which was like the end of e30 era. I guess Motronic 1.7 got more advanced ?

both the m42 engine and electronics are much more modern than the m20 e30.