Dual vs. single fuel pump

[erik325i]

I know the early 325s had a dual fuel pump setup, but the later model 325s came with a single pump. As far as I know, all years of the M3 had the dual fuel pumps. Why did BMW switch to a single pump for the late 325s?

As far as I understand the system, in the single pump system, the in-tank pump is a high pressure pump.
In the 2 pump system, the in-tank pump is a low pressure pump, and the second pump under the car is the high pressure pump.
Is this correct?

I'm just trying to better understand the fueling system before I upgrade my M3. I am planning on replacing the high pressure pump under the car with a Walbro 255. Since the in-tank pump is just a low pressure pump feeding the second pump, there is no need to upgrade that pump as well, right?

Thanks

Erik

[e30devo]

most automotive systems with two pumps the intank pump is referred to as a lift pump which essentially lifts the fuel into the line and what not, and youd be correct to think the second pump is the high pressure pump. you win!

you may have no need to upgrade the intank pump, but im sure a fresh one wouldnt hurt.

[E30Idea]

I know the early 325s had a dual fuel pump setup, but the later model 325s came with a single pump. As far as I know, all years of the M3 had the dual fuel pumps. Why did BMW switch to a single pump for the late 325s?

As far as I understand the system, in the single pump system, the in-tank pump is a high pressure pump.
In the 2 pump system, the in-tank pump is a low pressure pump, and the second pump under the car is the high pressure pump.
Is this correct?

I'm just trying to better understand the fueling system before I upgrade my M3. I am planning on replacing the high pressure pump under the car with a Walbro 255. Since the in-tank pump is just a low pressure pump feeding the second pump, there is no need to upgrade that pump as well, right?

Thanks

Erik

I have an early model with 2 pumps. I have installed 2 new pumps, and they work great. I am turboed and I plan on doing the same thing as you, a HP under the car and keeping the in tank the same. BUT, do you think at WOT for an extended period of time the under car pump will "outrun" the intank pump? This would be my only concern.

Thoughts?

[reelizmpro]

The intank is the transfer pump and the other is the main pump. They help each other so to speak. However, it can be expensive to replace them both. Some M3 guys have replaced the intank transfer pump with a Walbro 255 and eliminated the external main pump. I would go this route before spending almost $400 on two factory pumps. The trick is getting the Walbro to work with the stock pick up. I don't know if there is a direct replacement kit for our cars.

[BigD]

What if you already have new pumps, is it ok to just replace the outboard one with the Walbro, and leave the intank one? (ie, reiterating the question above, can the in-tank pump somehow get overwhelmed - it seems like a silly question but better to ask than to assume)

[reelizmpro]

What if you already have new pumps, is it ok to just replace the outboard one with the Walbro, and leave the intank one? (ie, reiterating the question above, can the in-tank pump somehow get overwhelmed - it seems like a silly question but better to ask than to assume)

I don't see a transfer pump keeping up with a Walbro 255lph. Why would you though? If you need to go with a Walbro, use it to eliminate both pumps. 255lph is sufficient for most applications. This way you'll be certain the Walbro is flowing as it should.

[erik325i]

I can't run a single high pressure pump.
I wanted to keep the stock low pressure pump to feed my surge tank, then run a Walbro 255 after that. It may be overkill, but I'm like that.
My fuel system is running at 5 bar (s50b32).

Erik

[nando]

get an in tank bosch 040

screw the chinese made walbro crap

[Jean]

Lol my early 318 is two pump system as well. It needs ALL the fuel it can get LOL

[Ara]

get an in tank bosch 040

screw the chinese made walbro crap

you mean " 044" and yes, im very tempted to go this route and keep my in-tank one or replace with a good condition used one.

http://cgi.ebay.com/ebaymotors/Bosch-044-External-Fuel-Pump-300-LPH-0580254044-NEW_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem4836bb5061QQitemZ310155890785QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

[Toms73NovaSS]

get an in tank bosch 040

screw the chinese made walbro crap

I can not see how you could get an 040 in the small tank hole we have with the sender tube etc.

you mean " 044" and yes, im very tempted to go this route

The 040 is the intank version.

[erik325i]

get an in tank bosch 040

screw the chinese made walbro crap

Bumping my old thread...

Is the Bosch 040 a direct drop in for an e30, or do you need to modify anything to make it work? (assuming it's going in a single pump e30 [325i]).

Both my e30s need fuel pumps. I think I'm going to get the Bosch 044 along with the stock in-tank pump for the M3, and the Bosch 040 for my 325i.

Erik

[nando]

it's just as direct-fit as an ebay walbro 255 :p

[ubernasty]

Kind of along these lines, i have a question that i've never got a solid answer on yet.

My 325e runs great all the time except on 95 degrees + days. The car runs fine for a little while but then just shuts off while moving and i have to restart and it runs ok for a minute or two and then shuts off again (repeatedly). Someone mentioned to me that the fuel pump could be overheating and failing.... anyone know of this in e30's??? Thanks.