In-tank Fuel Pump Modification

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Bav Ace
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In-tank Fuel Pump Modification

Post by Bav Ace »

The fuel pump in my car seized up last week and I have been looking into replacing it with an aftermarket fuel pump, specifically the Walbro 255lph.

I have been researching my options and like a few others on the board, I'm planning to delete the dual pump design and install a single in-tank pump. I also plan to modify the fuel pump carrier/sender to use 5/16” injection hose from the sender to the fuel filter. That leaves the issue of how to reduce the 12mm output hose to 5/16” at both ends of the in-tank output hardline. Others have addressed or are currently addressing this issue. I intend to attempt the following and wanted to get some feedback... good idea? bad idea?...let me know.

Details: Purchase two brass or stainless steel 3/8 to 5/16 reducing tube splices. The 3/8 side diameter of each must be reduced slightly to fit inside the 12 mm hardline. I was able to accomplish a test fit by chucking the fitting in a hand drill and using sand paper to remove the necessary material, which almost took longer to chuck up than reduce to the correct diameter. A lathe could also be utilized if available but my hope is to keep it simple enough that almost anyone can accomplish the modification.

This is a 3/8 - 3/8 splice I was using to test for fit
Image

The reduced fittings could then be soldered or brazed into the hardline. The hardline may need to be shortened to accommodate the difference in lengths of the original in-tank pump and the upgraded one.

Image

Note: The sanded fitting must be cleaned very well, especially if you intend to run both an in tank and in-line pump to ensure that small pieces of metal are not drawn into the pump...causing the original problem...rinse and repeat.

I am currently waiting for more parts to arrive but will update this thread as I progress
1st 5er
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Post by 1st 5er »

Eagerly watching and waiting. :D
slimdevil27
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Post by slimdevil27 »

Good solution. I would leave a gap before brazing or soldering. The reason being is that from the side the cross section would resemble a "T". The solder/braze would just be puddled on top of the T. With a slight gap you would get more surface area of contact, kind of like filling a "U", and you would get back flow into the first barb.

A 3/8 shaved down would be pretty close to 1/8 NPT. If so you could thread the inside of the pipe, the only advantage would be that pipe thread is self sealing. This would also depend on the wall thickness of the tube, but what you've got going looks great.
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Post by 1st 5er »

Would this method reduce the ID enough to restrict effective flow?
mooseheadm5
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Post by mooseheadm5 »

That is going to be too long for you to fit the pump at the correct height. To do that you will have to shorten the 12mm tube.
Bav Ace
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Post by Bav Ace »

mooseheadm5 wrote:That is going to be too long for you to fit the pump at the correct height. To do that you will have to shorten the 12mm tube.
I guess I chose a bad place to mention it in my original post. It should have been before talking about attaching the fitting. As you have said, I will need to cut back the 12mm tube and it will probably end up about 1-1.25 inch shorter to accommodate the difference in pump length and the fitting length. Also, I may choose to remove the outer most barb from each side of the fitting but I'll have to wait and see when I get the actual fittings in.

Moving inward from the outlet of the 12mm tube, the first blue mark is approximately where the walbro pump outlet will land when mounted with the pump inlet at the same level as the stock pump. The second little blip is nothing...The third is approximately where I'll have to cut the 12mm tube to accommodate the longer pump and new fitting length.
Image

Slimdevil27, I think I understand what you are describing and leaving a small gap sounds like a good idea. I also plan to wet each fitting so that there will be solder all along the length of the barb. Also, I am hoping that the solder will filling the barb valleys. Hopefully this would remove any voids between the fitting and tubing wall for fuel to flow in to.

1st 5er, If I understand your question correctly, flow restriction through the 5/16" fitting shouldn't be a significant issue because the minimum flow area occurs at the outlet of the pump itself and the area through the 5/16" still slightly larger. Also, if I remember correctly, the fuel filter barb is of similar internal cross-section as the 5/16" fitting. The 12 mm line has an ~9.5 mm id which is important for maintaining adequate fuel volume for the suction side of the main (in-line) pump but, with the walbro pump in-tank, the suction side is relatively unrestricted since is "sees" the entire tank volume.

Image Image
mooseheadm5
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Post by mooseheadm5 »

That's why I made this for wkohler:

Image

Direct fit with no cutting required. As soon as I hear back from my machinist I can get them made for production (it takes me waaaay too long to do them myself.)
Bav Ace
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Post by Bav Ace »

Interesting, I like the design. Is the piece press fit onto the tube and pump outlet? Is wkoler's pump the same length as stock? How is a seal formed between the aluminum fitting and the tube?
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Post by mooseheadm5 »

It has two fat O rings at the pickup tube and two at the pump and just slips on (with some force.) Kohler is also running a Walbro pump. The final design held over 100 psi with that pump. It will also work with the cheaper TRE pump, but will leak at above 80psi due to the design of the TRE outlet. For cars running lower than 5 bar, this isn't a problem. The pump must be secured to the support tube, though, since there is no other positive clamping with this design. I made little spacers so that the pump can be clamped to the return tube with hose clamps. I may try to make this with PTFE as well, which would allow positive clamping at the pickups, but I have read about creep with PTFE exposed to high frequency vibration, so I would prefer to be the guinea pig with that setup.
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my 745i solution

Post by IPM »

mooseheadm5
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Post by mooseheadm5 »

The rubber connector in the picture at that link is known to degrade and leak. Big issue for turbo cars and S38s to lose fuel pressure unexpectedly.
IPM
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Post by IPM »

mooseheadm5 wrote:The rubber connector in the picture at that link is known to degrade and leak. Big issue for turbo cars and S38s to lose fuel pressure unexpectedly.

Yea, it leaked in my 745i, put better quality rubber in, piece that came with pump was kinda soft. OEM is attached with hose, used something similar. A permanent hard partwould be nice.

The cheap pump has no problem fueling my stock 745i.
Bav Ace
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Post by Bav Ace »

Moose, with your fitting, does the pump output tube extend into the inside of the 12 mm tube
mooseheadm5
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Post by mooseheadm5 »

Bav Ace wrote:Moose, with your fitting, does the pump output tube extend into the inside of the 12 mm tube
It does.
Bav Ace
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Post by Bav Ace »

So I had some time to work on the fuel pump this weekend...in between torrential downpours...and thought I'd post on my progress.

I had some fittings made earlier this week...3/8 to 5/16

Image

Then a buddy helped me silver solder them into the fuel pump/sending unit carrier after I shortened the feed pipe.

Image Image



Before I assembled everything, I pressure tested the fittings to ~45 psi using co2 and a sink full of water.

The assembled fuel pump and carrier...
Image Image

I replaced all feed and return lines from the tank to the hardlines under the car with new gates 5/16" hose (rated to 225psi). So, now ill run it for a while and watch for any leaks to show themselves. I also went ahead an purchased a used
carrier in case something doesn't work out and I have to try again. Worse case, I'll have an extra one that's converted to the in-tank setup.
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Post by 1st 5er »

When do you want to host the clinic?
tn535i
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Post by tn535i »

Thought about a conversion like this myself for our e30 project since it needs a new in tank pump anyway. Couple questions?

Would it make sense to use the return line for the pump output since it is the right size for the 8mm hose to the filter then use the larger hose for the return?

Next ? is the part number for the walbro pump and how much they cost from where. I looked at one of the links and it was unclear which pump you would choose although they all looked to be about $100.
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Post by ElGuappo »

mooseheadm5 wrote:That's why I made this for wkohler:

Image

Direct fit with no cutting required. As soon as I hear back from my machinist I can get them made for production (it takes me waaaay too long to do them myself.)
Paul,
What kind of pump housing is that? Looks similar to the 1 piece pump/sender on my euro e23.
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Post by mooseheadm5 »

That is Kohler's Alpina pump housing with a Walbro pump on it.I checked and it works just as well on the US stuff.
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Post by ElGuappo »

How/where does the level sender attach?
On my euro e23, from the top at least, it does not appear to be a separate unit. And RealOEM supports that view also.
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Post by mooseheadm5 »

It bolts in from the top on that one. Don't know anything about the euro E23, though.
Bav Ace
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Post by Bav Ace »

1st 5er wrote:When do you want to host the clinic?
I am up for it whenever. Maybe next time there's a gathering nearby to do some wrenching I can bring along the gear to make the mods for those who are interested. Maybe if I get real motivated and can find some in the junk yards I'll make a few ahead of time and just trade them like a core swap...who knows.

tn535i, I think you could probably switch the return and outlet but you'd still have to deal with the 12mm to 8mm reduction at some point. I purchased the pump on e-bay from a vendor who has a physical store a few towns over. Shoot me a pm if you want the actual link to the one I purchased.

One note, there are many Chinese produced counterfeits out there that look very real but break very quickly, so, if the price seems to good to be true then it probably is.
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Post by wkohler »

ElGuappo wrote:How/where does the level sender attach?
On my euro e23, from the top at least, it does not appear to be a separate unit. And RealOEM supports that view also.
The pickup assembly should be essentially the same (though I'm not sure of the length with the 100L tank). Same design, though. The Euro pickups attach to the tank like the E30 pumps do - bayonet style. Also, the hole is smaller than the US one. The sender is held with the 4 nuts/studs just like on US cars.

I had to make a couple of adjustments to the mounting on Paul's setup. It is fantastic, but it wouldn't fit through the hole in the top of the tank. In fact, the Walbro is so much fatter than the stock lift pump that you cannot have the foam sheath on it either. It doesn't fit. Right now, I'm using his spacers and a couple zip ties. At some point, I'll pull it back out and use a slimmer hose clamping system.
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Post by ElGuappo »

Thanks Chris.
Does this unit screw out?
There are no bolts/screws visible when I remove the metal cover on the trunk floor.
RealOEM lists the same sender for the normal US and the euro 100l tank (with the conventional pump/sender setup tha tbolts in), Guess that means its just wider.
Mine is crenelated on the top rip too.
thanks
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Post by 1st 5er »

Bav Ace wrote:
1st 5er wrote:When do you want to host the clinic?
I am up for it whenever. Maybe next time there's a gathering nearby to do some wrenching I can bring along the gear to make the mods for those who are interested. Maybe if I get real motivated and can find some in the junk yards I'll make a few ahead of time and just trade them like a core swap...who knows.

tn535i, I think you could probably switch the return and outlet but you'd still have to deal with the 12mm to 8mm reduction at some point. I purchased the pump on e-bay from a vendor who has a physical store a few towns over. Shoot me a pm if you want the actual link to the one I purchased.

One note, there are many Chinese produced counterfeits out there that look very real but break very quickly, so, if the price seems to good to be true then it probably is.
If you can get the parts together, I can supply the cores and pumps, for two units.
I'll eventually need three, but two will work for now.

Will the 255 pump supply sufficient flow for the S38 variants under continued load?
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