Fuel Pumps

[gtopaul]

Has anyone noticed that there are a couple of different fuel pump designs for the E34? In particular, early E34's, M20 & M30, seem to use a design that has a attached fuel pressure regulator on top of the fuel pump. The outlet line comes out horizontally. It seems in 92 this design changed to a different pump without the externally attached fuel pressure regulator that has an outlet hose that comes out vertically. I decided that at 183k miles in my 92 M50 it might be a good idea to replace the pump as a preventive maintenance measure. When I pulled it out it was the earlier design but the hose clamps were replaced on both the outside and underside of the assembly as it bolts to the gas tank. I'm thinking someone swapped in an earlier pump at some time in the past. I looked through a number of different online part sources for the fuel pump and they list both designs as being correct for a 92. My car seems to run fine with the only noticeable problem being a slightly rough but solid idle at about 550-600rpm. I account that to be probably the injectors being old. My main question; is the later design fuel pump eqipped with an internal fuel pressure regulator or is there another fuel pressure regulator (m50 engine) somewhere else? I think all the engines require about the same fule pressure to operate properly. The earlier M20 & M30 engines have the fuel pressure regulator on the injector rail so it seems a little strange there would be two on the car. Perhaps the one on the pump isn't actually a fuel pressure regulator but more of a one-way valve to stop fuel from returning to the tank when the engine is shut off? Thoughts?

Thanks.

Paul L

PS Mounted second set of new 18" tires from the Tirerack two days ago (first set out of round) and already picked up a screw and had a flat. @#$%!
Sometimes you can't win.

[Bill R.]

vacum advance can looking thing on top of the fuel pump its a pulsation damper, it smoothes out the output from the pump so you don't have spikes up and down as it pumps. The check valve that is also on the pump is below that damper and below the fuel line. The fuel pressure regulating is done up at the fuel rail.






Has anyone noticed that there are a couple of different fuel pump designs for the E34? In particular, early E34's, M20 & M30, seem to use a design that has a attached fuel pressure regulator on top of the fuel pump. The outlet line comes out horizontally. It seems in 92 this design changed to a different pump without the externally attached fuel pressure regulator that has an outlet hose that comes out vertically. I decided that at 183k miles in my 92 M50 it might be a good idea to replace the pump as a preventive maintenance measure. When I pulled it out it was the earlier design but the hose clamps were replaced on both the outside and underside of the assembly as it bolts to the gas tank. I'm thinking someone swapped in an earlier pump at some time in the past. I looked through a number of different online part sources for the fuel pump and they list both designs as being correct for a 92. My car seems to run fine with the only noticeable problem being a slightly rough but solid idle at about 550-600rpm. I account that to be probably the injectors being old. My main question; is the later design fuel pump eqipped with an internal fuel pressure regulator or is there another fuel pressure regulator (m50 engine) somewhere else? I think all the engines require about the same fule pressure to operate properly. The earlier M20 & M30 engines have the fuel pressure regulator on the injector rail so it seems a little strange there would be two on the car. Perhaps the one on the pump isn't actually a fuel pressure regulator but more of a one-way valve to stop fuel from returning to the tank when the engine is shut off? Thoughts?

Thanks.

Paul L

PS Mounted second set of new 18" tires from the Tirerack two days ago (first set out of round) and already picked up a screw and had a flat. @#$%!
Sometimes you can't win.

[stevebuk]

There may also be a 'priming pump' mounted at the top of the fuel tank. I once fitted a silencer kit to the main fuel pump on a previous 5 series before realising that it was the priming pump making all the noise, I disconnected it and the car ran fine! :D

[imnprsd]

I own a 1992 525, and I think the one way valve (pressure regulator) you are looking for is locate in the engine compartment by the Mass Air Folow sendor.... between it and the fender side wall. But I'm not sure what this is. Just look for the fuel lines. Howerver, this may also be part of the fuel return line and not what you are looking for.

[genphreak]

..to work out what cars have what pumps statistically. BMW never said, so I guess they mixed them up a bit during production, maybe it was due to third-party supply problems (I doubt it). Maybe the e34.de guys (Kai?) would be able to shed some light on it, there might even be some Bavarian engineers in those forums... :) Nick