320i in-tank fuel pump???

[nightsurfride]

HI, I am trying to trouble shoot a no start on a friends 1982 320i, multi port fuel inj. 4 cyl. I found no fuel pressure in the system and disconnected the fuel line at the fuel distributor to find no pressure either. I disconnected the hose to the main fuel pump outlet and cranked the eng. while still no fuel was visible. While my friend continued cranking, I tapped on the main fuel pump and bingo, she flowed like a champ. So I figured it was a no brainer, and had him order a new fuel pump. He installed it, but still no fuel press. Now assuming he installed it properly, and yes there is plenty of gas in the tank and 12v available to pump w/ good ground, what is going on here? I am looking at a diagram of the fuel system and can see an electric fuel pump inside the fuel tank. I am unable to find any literature to explain why a fuel pump needs a fuel pump. If this in-tank pump were to fail, would that leave the main fuel pump high and dry? Any explanation of this "pre-pump", ideas of what may be the problem, or any help you could offer would be so much appreciated. Thank you.

 

[epj3]

The fuel pump pump's fuel up to the second fuel pump, which is the one that creates the fuel pressure.

I honestly can not think of a reason why it wouldnt be working unless that 2nd pump was bad, fuel lines clogged, or maybe the injectors are not working?

 

[Ben]

yeah, basically what epj said. the in tank fuel pump is the transfer pump that pumps the fuel to the high pressure pump. im not sure whether the fuel filter is before or after the high pressure pump, but that would be something to check. also on my car (1988 325) the in tank pump was accessable through a small plastic cover under the passenger side of the back seat, but that may not be the case. when you put the new pump in, could you still get intermittant pressure?
3 things to check-
in tank pump
fuel filter
all the above and more.

 

[KC Ron Carter]

Hmm

The intank pump on the e21 was an add on from BMW to prevent fuel vapor lock when the weather is hot and the fuel has alcohol as an additive.

The car will run just fine even if the intank is hosed.

I think it was added from 1979 on.

Here is a picture of the intank pump assembly.

Under the R/H rear seat.

Later,