Pre 88 dual fuel pump set up into post 88 single pump for 325i...

[cyrmanj]

Hi all:

I searched for this upgrade/mod and found anything. Is it possible? Can I upgrade my in tank and external fuel pumps with only one in tank pump as in 325i's built after 9/87? Has someone try this before?

The reason I am asking is because my external pump is buzzing and I may need to replace it, so I figured I can make an upgrade instead of just fixing:p. How about the Walbro DA-27 305 LPH, is this a good upgrade?

Thx!

[jlevie]

I don't know if the two pump assemblies are directly interchangeable (yet), but I suspect not or you'd find articles where folks have done that. In a week or two I should be able to answer that when I swap out my early (6/87) 55l tank with dual pumps to the later 63l tank with the single pump as I'll have both side by side during the swap.

Per the Bentley manual, nominal fuel flow on the OE system is 105lph. Using a pump with significantly higher capacity may overwhelm the FPR and result in excessive pressure in the rail, and perhaps lead to early failure of the pump. A pump in 120lph range sounds about right.

[slo325i]

Yea... i actually dealt with this problem a week ago as my intank pump on my 87 325i went bad. I went to a pullapart and pulled a intank pump from a 85 318. Was hesitant at first but the parts look the same and the car runs like new again.

This prolly doesn't help you as you need a external pump. Try a pullapart??

Justin

[Slangbox]

Hmm, I'm very interested in this--mine is buzzing too and I think upgrading (if it's possible) would be a better investment in the long run, as there would be one pump to go bad instead of two.

[slo325i]

It's weird because on my '87, there seems to be two hoses that go in and out of the in-tank fuel assembly. My '89 only has one hose that comes out of the in tank fuel pump. I don't know how you would deal with the other hose if you were to upgrade to just one pump. Kinda hard to explain...

[jlevie]

It's weird because on my '87, there seems to be two hoses that go in and out of the in-tank fuel assembly. My '89 only has one hose that comes out of the in tank fuel pump. I don't know how you would deal with the other hose if you were to upgrade to just one pump. Kinda hard to explain...

The fuel system is very different on either side of 9/87.

The most obvious difference is the dual pump configuration, but there are other differences as well. Early cars (up to 9/87) have the fuel return going into the right side of the tank where the lift pump is. There's a cross-over tube between the left and right sides of the tank to equalize fuel level. Late production has the fuel return going into the left side of the, which feeds a syphon that transfers fuel from the left side of the tank into the right side of the tank.

Now that I think about it, that alone suggests that you can't use the later pump in an early tank. Even if the pump will physically fit you have no place for the fuel return. I have seen a case where an aftermarket high pressure pump was used to replace the in-tank transfer pump by modification of the in-tank pump assembly.

[e30lyf]

^^^ soo 10/87 production it's not dual pump?

[cyrmanj]

Now that I think about it, that alone suggests that you can't use the later pump in an early tank.

I see, that leaves room only for an aftermarket/non OEM in tank pump.

^^^ soo 10/87 production it's not dual pump?

According to ETK, that is correct.

I consider myself a purist, however when there's room for improvement it's worth considering it. So far I am inclined to use the OEM dual pump set up. I'll check both pumps according to Bentley's procedure, determine which one is not doing the job right and replace it or fix it.

I've also heard that the buzz could be a semi clogged pump or fabrication defect, is this correct? I've been running my buzzing pump for over a year without any fuel delivery issue, however I'm getting tired of the noise, hehe.

However if someone knows and easy "Walbro DIY upgrade", please share. ;)

Thx for all the comments!

[twright]

My external pump buzzed when the internal pump wasn't working. I changed the internal (intank) pump and the external buzzing stopped.

[jlevie]

I've also heard that the buzz could be a semi clogged pump or fabrication defect, is this correct? I've been running my buzzing pump for over a year without any fuel delivery issue, however I'm getting tired of the noise

The high pressure pump will buzz if it is worn or it is working too hard. The former can be just a result of age, but if there is rust in the tank it will wear out a pump pretty quickly. The latter can be caused by a clogged filter, failed transfer pump or obstructed fuel line.