# 320i in-tank fuel pump?



## nightsurfride (Jan 28, 2004)

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. uch:


----------



## AndDown (Jun 17, 2003)

nightsurfride said:


> 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. uch:


I had a '77 320i that started jerking and cutting off sporadically - was diagnosed to have some kind of contamination in the fuel tank, possibly from muddy runoff during a rainstorm that seeped into the gas station's tanks. Dealer had to remove the entire fuel tank and have it steam cleaned(?) and change the fuel filter - it was all clogged. You might want to have your filter checked as well as the injectors.


----------



## The Roadstergal (Sep 7, 2002)

If your 320 is set up like my 325, there's a main pump outboard and a transfer pump in-tank. There's a particulate filter on the transfer pump - one thing to do is pull the transfer pump from the tank and clean that filter. The main pump will have trouble pulling fuel if the transfer pump is clogged - or if it isn't running (the transfer pump is fuel-cooled, so if you run near empty, you can burn it out). Also, the easy stuff - check connections, and put in a new fuel pump fuse and relay.

Get a Bentley - they're great.


----------

