In-tank Fuel Pump Modification

E28 technical advice asked and given! Troubleshooting, modifications and more.
1st 5er
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Joined: Jun 13, 2008 12:15 AM
Location: Cypress
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Re: In-tank Fuel Pump Modification

Post by 1st 5er »

:wave:
Bav Ace wrote: Jan 31, 2012 12:31 AM 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

It's good to see that this thread has been so helpful.

Happy 4th, y'all. 🇺🇸
Philo
Posts: 2197
Joined: Feb 12, 2006 12:00 PM
Location: Long Beach, CA

Re: In-tank Fuel Pump Modification

Post by Philo »

Update on my custom fuel pump and hanger. After pulling the inspection cover I found that the pump in the car had a brass fitting soldered to the high pressure hardline and was already using the smaller diameter rubber fuel hose. I believe this was done by the shop that helped withe the initial engine swap back in 2012. God, time flys. So I measured the old setup, cut the new hardline, and braised a brass fitting to the new hanger hard line and pressure tested the connection using some argon. I also had CO2 but the small argon tank was just easier to work with. I don't think it matters what you use, as long as it's non flammable and under pressure. Tested everything under water, all good, no leaks.

Items remaining, Still need to wrap the pump with some silicon padding and then strap it to the return line. I also ordered a new URO level sender which was 25% of the cost of the BMW part. Hope it works.

Here's some pics.

https://www.dropbox.com/scl/fi/s91mkcb5 ... 3h091&dl=0

https://www.dropbox.com/scl/fi/wsl5gm7a ... 96wlj&dl=0

https://www.dropbox.com/scl/fi/xejnhr2p ... i9i8s&dl=0

https://www.dropbox.com/scl/fi/7z4tezkz ... 0d2tr&dl=0
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