Do I need the in-tank fuel pump?

[dennislarson]

I had a fuel delivery problem that I solved by cleaning the varnish off the prefilter in the tank. I discovered that the in-tank fuel pump has never worked since I've had the car, about two years. It seems to run fine without it. Do I need it? It's an '83 320is.
Thanks

[epmedia]

You don't need an in-tank pump as long as the old in-tank pump has not been modified to be a ticking time bomb, and the pickup tube/pickup filter works well.
Oh - you also need new hoses on the suction side of the external pump (total 3 hoses) if they have not been replaced already (original OE hoses probably suck air bubbles).

Edit: oopsie, is the dead pump still installed?
When I read "Do I need it"? I automatically thought the dead pump was removed.

[sbcrockett]

careful though. I thought that without an in-tank pump, your external could burn up and die or at least not live as long as it should.

just what I've heard...

+1 on the hoses.

[epmedia]

careful though. I thought that without an in-tank pump, your external could burn up and die or at least not live as long as it should.

just what I've heard...

+1 on the hoses.

Edit: I was assuming the dead pump was removed. You are correct, a dead pump needs to be replaced, or removed.

Both my '78s did not come with in-tank pump, stock.
My external OE '78 pump was replaced in '99 because is was stuck. I unstuck it and made it a spare and started using it on my other '78 at about 2005. That old pump probably still works

The only issues I've seen so far with one pump are the same issues as having 2 pumps, but with only one pump to worry about.

Now if an in-tank pump fails, that could cause damage to the external pump if it leaks-by just enough to make the engine run.
Just like having clogged filters causing a pump to overheat. Some aftermarket pumps have overheat protection, which is very good.

[Layne]

You can go without th in-tank pump if you replace it with a piece of tube. You cannot leave a non-operation pump in there. It will damage the main pump.

[ekr470]

Just curious. Has anyone ever done a system pressure test with and without the pump? The in-tank pump could be worth a few extra psi.

[Rudolph320i]

With my 83 320i when the in-tank pump quit the car wouldnt run.

[shauer]

The in-tank pump was not originally part of the E21 design. My '77 was manufactured without the in-tank pump. I don't think it was officially added until some time in '78 but I could be a little off on that date. There was an issue with some of these early cars experiencing vapor lock in the fuel supply line between the tank and the external pump in warmer climates. The solution was to add the in-tank pump to help lift the fuel out of the tank and eliminate any vapor lock issues. The in-tank pump was added to the early cars as part of a service update / recall. When I was running kjet on my car, the in-tank pump was connected to the harness with some crimp-type connectors that were obviously done by the dealer and not the factory.

I did a little searching several years ago and found references in old Roundel issues as well as some other documentation explaining this "recall" and addition of the in-tank pump.

So, the in-tank pump has nothing at all to do with fuel pressure, and you can run without it just fine as long as you are not having vapor lock issues with the main fuel pump supply line from the tank.

With that said, keep in mind that all of our cars are between 29 and 36 years old. If you are some how still running with the original main pump in your car then almost anything is possible as far as what is needed to keep it running.

- Steve

[eseeling]

The in-tank pump was not originally part of the E21 design. My '77 was manufactured without the in-tank pump. There was an issue with some of these early cars experiencing vapor lock in the fuel supply line between the tank and the external pump in warmer climates. The solution was to add the in-tank pump to help lift the fuel out of the tank and eliminate any vapor lock issues. The in-tank pump was added to the early cars as part of a service update / recall. When I was running kjet on my car, the in-tank pump was connected to the harness with some crimp-type connectors that were obviously done by the dealer and not the factory.

I did a little searching several years ago and found references in old Roundel issues as well as some other documentation explaining this "recall" and addition of the in-tank pump.

So, the in-tank pump has nothing at all to do with fuel pressure, and you can run without it just fine as long as you are not having vapor lock issues with the main fuel pump supply line from the tank.

With that said, keep in mind that all of our cars are between 29 and 36 years old. If you are some how still running with the original main pump in your car then almost anything is possible as far as what is needed to keep it running.

Hope this clears some things up.
- Steve

Ditto for my '77. I removed the crimp-on aux pump (shorting connectors) and it ran fine until I was at 10,000 feet on a Summer day, and it vapor locked.
Has anyone ever installed a high volume in-tank pump on their car? I have a 300 hp goal.

[pommeree]

This is strictly anecdotal as I don't see the connection but ...
I had a problem with gas cutting out with a low (not empty) tank in long right-hand turns like on-ramps.
This went away after I replaced the dead in-tank pump.
It was frustrating to have to tip-toe down on-ramps if I had ~1/4 tank.
Not any more!

[Layne]

Just curious. Has anyone ever done a system pressure test with and without the pump? The in-tank pump could be worth a few extra psi.

The pressure is determined by the fuel pressure regulator. You cannot increase the pressure except by shimming the regulator.

[tomscat1]

This is strictly anecdotal as I don't see the connection but ...
I had a problem with gas cutting out with a low (not empty) tank in long right-hand turns like on-ramps.
This went away after I replaced the dead in-tank pump.
It was frustrating to have to tip-toe down on-ramps if I had ~1/4 tank.
Not any more!

This kind of question comes up here from time to time... and I don't feel that I am nearly enough of a mechanic or an engineer to second-guess BMW on these things. There are no doubt some folks in here who are competent enough to do that, but I am certainly not one of them. I just trust that, if BMW put something in there, they did it for a reason... and why would I NOT keep it in there.

I tend to fall back on the quote that our site moderator, Kevlar, has at the bottom of his posts:
"Let me get this straight... You are swapping out parts designed by hundreds of engineers that get paid thousands of dollars for something you bought at Pep Boys because your buddy who doesn't have a job told you it was 'better'?!? "

I love that. Makes me chuckle every time I read it.

[shauer]

Just to clarify, I was not advocating going out there and removing your in-tank pump. Yes it was added to improve reliability.

I was just pointing out that the in-tank pump is really an after-thought to correct an unanticipated problem and there are cars out there that ran fine without it.

- Steve

[ekr470]

The pressure is determined by the fuel pressure regulator. You cannot increase the pressure except by shimming the regulator.

Are you sure? Whether or not I have a high or low volume pump, I will have negligible pressure if I do not have some sort of restriction to create the pressure. If i kept putting a larger and larger volume pump on there, eventually the diameter of my pipe (hose) would come into to play and I would began to increase pressure. In the same way, given a fixed oriface, if I increase the volume (or ability to pump fluid) would i not also increase pressure? Not sure I'm thinking about it the right way but it makes sense in my head

[Layne]

Are you sure? Whether or not I have a high or low volume pump, I will have negligible pressure if I do not have some sort of restriction to create the pressure. If i kept putting a larger and larger volume pump on there, eventually the diameter of my pipe (hose) would come into to play and I would began to increase pressure. In the same way, given a fixed oriface, if I increase the volume (or ability to pump fluid) would i not also increase pressure? Not sure I'm thinking about it the right way but it makes sense in my head

Right, but the pressure reg is not a fixed orifice. If you increase the flow, it will just open wider so the pressure stays the same.

If you somehow increased flow to the point that the pipe restricted it, the pressure would only increase on the pump side, not at the front of the car. The point where the gas enters the skinny pipe would become the restriction and the pressure would then drop inside the pipe.

[ekr470]

If you increase the flow, it will just open wider so the pressure stays the same.

Ok, that's what I was missing in the equation.

[epmedia]

My first posts were assuming the dead pump was removed.
If the dead in-tank pump is still installed, yes it needs to be replaced, or removed.
My bad...

[dennislarson]

Thank you gentlemen. That gives me just what I need. My old nonworking pump is still in there and I will remove it and replace it with a hose to be able to use the prefilter/suction part. I am at sea level and it doesn't get too hot here so I think I'll be OK. If I have any vapor lock problems, I'll replace it. You just saved me a couple hundred bucks. Getting a used one at Pick-Your-Parts is probably not a good idea since it will probably be at least 28 years old, unless I can find one that has been replaced.
Thanks again.

[Layne]

It may not be that easy to attach the screen. I machined an adapter to attach it to a copper pipe. I botched it a little though and could never fit the fuel level sensor in there.

[gsumzzz]

my car has a 9/77 build date and internal pump was factory installed. still performing well.

[dennislarson]

Has anyone tried gutting the motor rather than trying to replace it?

[jjgbmw323]

Has anyone tried gutting the motor rather than trying to replace it?

LOL. Yeah man I gutted my whole car's engine and threw it away, thats why Its not running right now.
And I have to replace the in tank fuel pump, mine is shot. When I do the gas tanks I am replacing it...

[lasvegascop]

Ok....my 2 cents on this is:

If you only have a pump outside the the fuel tank, then the early pumps were having hard time getting the fuel out to them if the tank ever ran dry. To explain this easier, have you ever try to siphon gas out of the tank? Well, you have to "suck" on the hose and be below the fuel line to have the gas going.... if the pump cant "suck" the fuel out of the tank then its a huge problem and the car wont run.

I have installed a high performance, high volume in-tank pump and got away from the external pump all together. Most of the newer cars run this way. No matter what brand....even GM models ie Camaros, Buicks etc...



In tank keeps them cooler and last longer...

[npover72]

Lasvegascop,

I assume that the new pump you have in that pic is aftermarket and not a stock replacement. Knowing how expensive an OEM pump and sender runs, did you pay just as much or was there considerable savings in buying the aftermarket one?

[lasvegascop]

The after market one was way cheaper....I think I paid like $80? I forgot, I look for deals and best quality. Spend tons of time on measuring things and quality.

Hope this helps?