Fuel Tank / Pump upgrade

[Jean]

I have an early car with a small fuel tank and TWO fuel pumps. The late model fuel pump won't drop into my fuel tank w/o some modifications. The intank fuel pump has a return line on it it, but the late model pump does not.

So, since I already have a late model 325i fuel tank that I can't sell I am thinking about upgrading my small tank in the car to this tank with 1 pump.

I've dropped the tank on the late model car before, but never on the early car. So my question is regarding any differences in regards to fuel and evap lines, are they all in the same spot? Any major problems in doing this swap?

I want to basically eliminate the external pump, end up with just one pump and a bigger tank.

Here is the tank in my car, it gets full with about 11 gallons. My car in city is getting about 20-22mpg, and on long trips it did about 25mpg.





The problem I am seeing with this right off the bat:

a) the late model tank uses TWO fuel level senders, and my car only has ONE opening under the back seat. So it's not the problem with wiring it, but not having a 2nd "cover" under the back seat for access.

The late model tank pictures:





The more I look at this the more I think it's not worth the hassle?

[jlevie]

The late model tank will fit in with no problems. You will have to re-route the fuel return line and the filter. For the gas gage to indicate properly you'll need the cluster from a late model car.

[Jean]

Yeah I know about the gauge. I have a late model cluster with the early gauge, since the gauge works on it's own and needs to match the tank/sender(s), that's the only component that needs to be changed in the cluster.

My concern was with the lines. I am thinking I can still keep the fuel filter where it is (near the engine)...but I am not sure if any other lines (fuel evap lines) are different?

[j0nny5]

bump im trying to do the same thing,have to figure out a return,and i have 3ft of hose to eliminate the external pump,theres other lines on my 85 eta but not sure if they go in the tank,anybody done this or know what line enter tank?

[Jean]

Hmmm... I am wondering if ditching the inline (external) pump and putting aftermarket walbro or the like pump in the tank would be ok?

[Dave]

Hmmm... I am wondering if ditching the inline (external) pump and putting aftermarket walbro or the like pump in the tank would be ok?

sure, or just use the late model single in tank pump.

[Jean]

The late model in tank pump is different from the early in tank pump though.... one has a built-in return line.

[Dave]

yeah - I thought you meant you were putting in the late model tank. If so, you will need to use the late model pump, or at least its frame for a walbro.

[Jean]

Trying to see what my options are w/o doing the tank swap.... I had some fuel starvation issues at the last autocross. Would it be ok to keep the tank, drop the external pump and upgrade the internal pump?

Doing a tank swap is just a messy job I don't want to do right now...if I end up doing that I'll of course use the late model tank and i'll need to swap the fuel gauge again to match the two senders.

[jlevie]

The best solution would be a tank swap, but short of that you may be able to fix your starvation issues.

With the dual pump setup there are only two reasons to have fuel starvation issues. One would be a problem with the pumps and the other would be a layer of rust sediment in the bottom of the tank. Fixing the first problem is usually just a matter of replacing a failed in-tank transfer pump, but if the high pressure pump is noisy it may also need to be replaced. If the tank has a layer of rust sediment in the bottom, that sediment can get stirred up in spirited driving, collect on the inlet screen of the pump and choke off flow. It that's whats happening only a replacement of the tank or acid cleaning & sealing it will solve the problem.

[Jean]

I've replaced the fuel level sender on this tank before and the external pump (was getting noisy) and have also drained the tank and looked inside with a flashlight...it looked clean. So, maybe it's the in tank pump that's failing or the external pump again (it's a little noisy still).

The external pump is the high pressure pump and the in tank is low correct? It works fine when you eliminate the external pump and put a high pressure pump in the tank?

[jlevie]

If you replaced the external pump with a new unit recently and it is again getting noisy, something is taking out that pump. A failed in-tank transfer pump, rust in the tank, or an obstruction in the fuel system that is making the high pressure pump work too hard are all possibilities.

[Jean]

I replaced it with a used pump, it was a little noisy right off the bat but much quiter than the one that was on there. I'll replace the in-tank pump next.

But, would the system work ok if I ditch the ext. pump and only run the in-tank or will not provide enough pressure? I would rather just have one pump to deal with.

[jlevie]

If you replace the in-tank transfer pump with a high pressure pump you could eliminate the external high pressure pump. In the process you'll have to provide a fitting for the return line from the engine bay. The two pump system has the return in the flange of the low pressure pump and the later single pump system has the return going into the left side of the tank.

[Jean]

If I am keeping the same older style tank and the older style in-tank Housing, and just replacing the pump in that housing with a high pressure pump why do I need to do anything with a return line?