In-tank Fuel Pump Modification

[Mike MPD]

@davintosh did it right (as usual). Do as he said.

(I did it right on Minerva).

I am getting ready to do the single in-tank fuel pump conversion myself.

I was already leaning towards the davintosh method, but seeing you mention that you used his method as well on Minerva helped confirm my decision.

I was curious if you ended up extending the new return line (previously the feed line) or if you left it alone. Any other problems, regrets, etc. since the install?

I just re-browsed your entire minerva thread and didnt see details on the fuel pump install but I apologize if I missed it.

Thanks!

[tig]

@davintosh did it right (as usual). Do as he said.

(I did it right on Minerva).

I am getting ready to do the single in-tank fuel pump conversion myself.

I was already leaning towards the davintosh method, but seeing you mention that you used his method as well on Minerva helped confirm my decision.

I was curious if you ended up extending the new return line (previously the feed line) or if you left it alone. Any other problems, regrets, etc. since the install?

I just re-browsed your entire minerva thread and didnt see details on the fuel pump install but I apologize if I missed it.

Thanks!

I didn't extend the new return line. All three cases where I've done this are still working great.

[Mike MPD]

So the two wires going to the original main pump should be connected to eachother or no?

One is green/purple other is brown. I've tried both ways but I'm getting no start after new pump. Just pulled out the new in tank pump to double check wiring and tested it on the bench and all seems well.

Starting to go down the diagnosis tree

[Shawn D.]

So the two wires going to the original main pump should be connected to eachother or no?

NO!

That would be creating a dead short from power to ground!

I've tried both ways but I'm getting no start after new pump.

You're getting nothing now because you blew the fuse, damaged the relay, and/or damaged the wiring. Hopefully, it's just the first one.

[Mike MPD]

So the two wires going to the original main pump should be connected to eachother or no?

NO!

That would be creating a dead short from power to ground!

I've tried both ways but I'm getting no start after new pump.

You're getting nothing now because you blew the fuse, damaged the relay, and/or damaged the wiring. Hopefully, it's just the first one.

OK thanks that's what I thought, and how I had it. I'll do some more diagnosing this weekend.

[Galahad]

NO!

That would be creating a dead short from power to ground!


You're getting nothing now because you blew the fuse, damaged the relay, and/or damaged the wiring. Hopefully, it's just the first one.

OK thanks that's what I thought, and how I had it. I'll do some more diagnosing this weekend.

You almost certainly blew fuse 1, I'd be surprised if you damaged the relay or wiring. Not saying it can't happen, but as crappy as the torpedo fuses are they still are fuses.

[Mike MPD]

Nothing blown, nothing damaged, power wasn't even getting back there.

Car is running now, turns out I knocked something loose under the dash when I was replacing the clutch master.

An added benefit of davintosh method I did not consider, if you don't bother extending the new return line its really easy to fit the pump into the tank.

[Shawn D.]

Nothing blown, nothing damaged, power wasn't even getting back there.

Car is running now, turns out I knocked something loose under the dash when I was replacing the clutch master.

Glad to hear it! Inadvertently doing something like that can be extremely frustrating!

[Philo]

On page two Charlie (Cek) noted his stock pump total length at 22.5 cm. Wondering if anyone knows the total allowable length. I'm putting in a Deutchwerks 340 pump to drive my S54 and I need 23cm or even better 23.5cm.

Lmk if anyone has ever dropped a ruler down into the tank and measured the depth.

Thx.

[Philo]

Finished my intank fuel pump upgrade. I used an aftermarket ebay hanger, hacked it up and mounted the DW300 rated at 340 lph @ 40 psi. More then sufficient for a street S54. Still need to add some rubber padding around the motor and strap it to the return post but pretty much done.

The total length from the rubber seal to the end of the pickup screen is 23cm. .5cm longer than what cek noted for a stock e28 pickup pump assembly. Hope I don't hit bottom !

For reference I'm replacing the pump in the car because the rail pressure is 10 psi low and the residual fuel pressure bleeds out to zero after 30-40 minutes with no visible leaks under the car.

Will report back after the install.

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

[Mike MPD]

My pump recently popped off the hanger after a little over a year with no issues. I ended up adding a flare to the metal line on the hanger and left everything else the same per the davintosh method.

The hose clamp still seemed tight on the line and I didn't really think there was enough vertical room in the tank for the pump to come off the hanger. I ensured it was the same height as the stock assembly as well. I think I may have even added an 1/8 inch or so to ensure it was sitting on the bottom of the tank.

It doesn't seem that anyone else has had that issue but hopefully that sorts it for me.

[Philo]

I didn't flare the pressure side of the hanger hard line after I cut it because I can't imagine how the pump could slide off. I might take the system apart and put a minor flare on the end.

Thx for the tip !

[Chicagotrader92]

I have had success with the in-tank fuel pump mod for about 6 months. It eliminated my long crank issue on hot starts, which I'm 90% sure was due to the original intake fuel pump.

1) Replace your fuel filter while doing this.

2) Replace the fuel hoses from the tank to fuel filter while you're in there. You can use standard fuel hose (not from BMW) if you are trying to save a $$$. You can attach the new hoses to the old hose and feed it through. Eliminating the need to drop the tank a bit.

- https://www.amazon.com/dp/B09KRVK9M9?re ... tails&th=1

- https://www.amazon.com/dp/B07S8GBGYX?ps ... ct_details

3) I used these 8mm to 12mm adapters. (I'd order more than you need)

- https://www.amazon.com/dp/B088QKY73K?re ... tails&th=1

[1st 5er]

... You can attach the new hoses to the old hose and feed it through. Eliminating the need to drop the tank a bit.

- https://www.amazon.com/dp/B09KRVK9M9?re ... tails&th=1

- https://www.amazon.com/dp/B07S8GBGYX?ps ... ct_details

3) I used these 8mm to 12mm adapters. (I'd order more than you need)

- https://www.amazon.com/dp/B088QKY73K?re ... tails&th=1

Excellent contribution.

[davintosh]

I'd be hesitant to use standard fuel hose in the tank.

I didn't really think about that much beforehand, but on both of the cars I've done, the pumps came with a kit that included a section of fuel hose. Looking back at it the site I bought the most recent one from, it doesn't specifically say it's submersible, but since the vendor specializes in fuel pumps I think it's safe to assume it'll work.

https://www.highflowfuel.com/genuine-wa ... -gss340g3/

Well now… I was just reading through some of this thread and came across this, THAT I WROTE, and now know that I have some work to do…

I started having some severe hesitations/misfiring/etc. issues with my car last fall, and life didn’t allow much time to do much with it until last month. I’d been checking all kinds of potential issues — compression, electrical, ignition — and wasn’t getting anywhere.

There’s a new kid in town — Craig — who retired from his career as a BMW tech and trainer in the LA area and relocated here to be closer to family; he stopped by and diagnosed the problem as low fuel pressure in the first few minutes. I later confirmed that with a fuel pressure gauge, then started checking some things. I knew I had hit paydirt when I pulled the pump assembly, and the pump was just dangling by the wires! Dang.

So I figured that the lack of a retaining ring/bump on that pipe was the reason it slipped off, and maybe I didn’t tighten that hose clamp properly… And that short piece of hose that I used that came with the pump felt a little soft, so I cut a chunk of fuel hose to fit (standard high-pressure fuel hose, btw) and put it back together. And when I cranked on the top clamp, I slipped a notch. Cranked again and it slipped again! So that’s why the thing came loose!


But now as I read my own caution about using standard fuel hose, I know that I’ll be needing to tear into it again to put some proper submersible hose on it. I had also thought about using a flaring tool to add a bump to the bottom of that pipe on the assembly to prevent it from slipping. Ever.

I will. Thank you.

Like I remember. I'm regularly doing mye28.com searches on topics, finding threads with great writeups on how to do things, and then discovering that I'm reading something *I* wrote. ADHD FTW!

Right there with you, Charlie!

[1st 5er]

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


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.



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]

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