Fuel Pump

#1

So I am in the process of putting together my e30 for HPDE and eventually specE30. I have it stripped down and I am looking over everything that I want/need to replace. I notice the rubber sections of fuel lines look old and will need replacement. I’ve heard there is a change in the fuel delivery system, from an external pump to an internal pump? My car is an 87is and what I see is an external pump near the fuel filter. Also the gastank has a crossover pipe so I’m guessing there is another pump on the passenger side (in tank)? My question would be, what is the optimal fuel set up (what style pump, tank, lines ect…)?

#2

An 87 325is should have an external high pressure pump mounted just in front of the left rear wheel and an in-tank transfer pump mounted in the right side of the tank.

#3

The general consensus seems to be that the later style single pump and tank is the optimal fuel setup to avoid any fuel starvation issues.

#4

King Tut wrote:

In my experience neither system (early or late) is inheritly better. An early tank that has no rust and a good pumps can run as low as the later style tank w/o starvation. Conversely, the later tank with a weak pump will starve at below a half tank.

That said, the later style tank can be fitted with a transfer pump in the left side. That will allow the tank to be run down to about three gallons before starvation begins.

#5

Any thread or info on part numbers and procedures for the second pump?

#6

The photo shows the end result. I used a BMW transfer pump as is used in the early tanks in place of the level sensor that is normally on the left side of the tank. It was necessary to file a bit off of one of the locking ears of the tank to get the pump to mount. The 3/8" tubing that runs across the tank has a bushing soldered to the end to match the ID of the hose from the transfer pump’s outlet. Not visible is the tube that is soldered into the elbow that goes into the fuel cup, generally following the curve of the existing siphon outlet tube. I pop riveted a plate of 1/4" steel to the top of the tank that I threaded to accept the elbow. The plate and the elbow was sealed with JB weld. There is very little clearance between the tank and body and I had to space the tank down 3/8" for clearance.

An alternative to modifying the tank would be to use the high pressure pump from a late model 318is. It has a fuel return fitting as a part of the pump housing. I found that out after I’d made this mod.

A problem with this setup is measuring fuel level. In the stock configuration the sensors are wired in series with only the right side sensor being ground referenced. The sensor that fits into the transfer pump harness is ground referenced, so just wiring them in series won’t work. I was able to isolate the left sensor from ground by opening up the mounting holes, using insulating sleeves on the studs, and insulating gaskets on both sides of the sensor. A better solution, with a smart dash, would be to read each sensor separately and sum the result in the dash.

A better solution, in my opinion, would be to fit the tank with a pair of transfer pumps and feed their output to a four port surge tank that feeds a high pressure pump. The legality of that is even more iffy than what I did.

#7

So I finally got my secondary pump in, and I have a question about the wiring. The new pump from Bosch has a positive and negative terminal, yet the Bentley doesn’t seem to reference them, and the wiring doesn’t make it clear which connector goes to which terminal. Does it make a difference?

#8

I can’t tell you which wire goes where, but I’m pretty sure it makes a difference. Motors run backwards when you switch there wires around. If the wires are colored black is neg and red or green is positive. Solid brown is always ground/neg.

#9

The OE pump and OE wiring can’t go togther but one way as the studs on the pump and the ring terminals are different sizes. If you are using an OE pump you’ll have to figure out which wire is ground and which is power. In general, a brown wire will be ground.

#10

The studs are definitely different, but the ring terminals looked identical to me. I will check that again tomorrow. The wiring is all covered so you can’t really see the wire colors either.

#11

Well I ended up wiring it up the way it was before. I got everything in and she fired up so hopefully I did everything right and no more fuel starvation. I will run it at Road Atlanta till she stumbles.