In-tank Fuel Pump Modification

[1st 5er]

Ah! then we are on the same boat

Based on your signature, we drive the same car.

[Ju@n]

Ah! then we are on the same boat

Based on your signature, we drive the same car.

car/boat/aircraft carrier

[onesidedsquare]

Just did this mod with the Tru pump,
AND IT IS GREAT, totally worth it, some troubleshooting notes

Don't use the worm clamps, nearly each one leaked, get the right fuel clamps the first time
Don't test the pump out side the tank, as its not grounded and will burn thru a few fuses while you figure it out
I used a smaller hose to go inside the bigger hose at the pump and the filter and it works just fine
Don't connect the inline fuel pump wires (am idiot) as it will burn thru a few fuses while you figure it out, just tape them off

[1st 5er]

Just did this mod with the Tru pump,
AND IT IS GREAT, totally worth it, some troubleshooting notes

... will burn thru a few fuses while you figure it out.
... will burn thru a few fuses while you figure it out,

I like your attitude.

[EE TWO EIGHT]

Is the stepped hose that goes between the pump and in tank assembly still available new? Part number if available or a link to where I can order one?

[1st 5er]

Is the stepped hose that goes between the pump and in tank assembly still available new? Part number if available or a link to where I can order one?

Not sure, but all the OE stepped pieces I've seen are rubber and not designed for high pressure application.

[harrypalmer]

BTW and FWIW, had previously commented having some sort of hiccups with my own pump mod, but I was wrong as it is only susceptible when the fuel gets too warm (very particular to my car). Will be installing a fuel cooler next week and report.

A year later, have installed a E28 specific fuel cooler. It does greatly improve the engine's drive ability in traffic. However, the fuel starvation is present when pulling hard (4,500 to 6,500 rpm via a D'sylva chip) which is the way I mostly drive. Anyway, I am going to take the intank fuel pump out and get a dedicated submersible fuel hose like Davintosh suggested earlier. And report back again.

Does anyone out there, have experienced fuel starvation with this fuel mod?

As a follow up I am glad to report that I've found my in-tank TRE-340 pump mod came totally loose from the pump hanger so obviously that was the fuel starvation cause and symptom.

However, since I was prepared to war, not knowing what to expect; I re-tightened it to the hanger, and then proceed to (unmod) my mod and reinstalled a fresh 8X13 hose to a main Quantum High-Flow Pump 603 (underneath). Ended up not using a submersible hose previously purchased as I kept the halved rubber reducer from the original Bosch pump instead for the in-tank pump.

So, contrary to advice I truly respect and mostly do follow, it seems the two high-flow pump setup is getting along fine, even in the heat of mid September. Car has been running fantastic ever since with no fuel starvation or hesitation. I'll report back further more if the need arises.

[davintosh]

Is the stepped hose that goes between the pump and in tank assembly still available new? Part number if available or a link to where I can order one?

Just eliminate the need for it by using the small pipe on the tank assembly for the pump output. I've done that on two cars now, and it works fine. Very easy modification, and allows you to use the connector hose that comes with the pump.

This is the one I did several years ago for my 528e:



And this is the one I did last year for my M535i:

[ericboston]

Hi gang - thanks to you all, including you, cek and davintosh, for all your insights and banter around this subject. I just finally finished my conversion using all the excellent documentation and hard knocks. So - sorry to bump this up, but I wanted to provide my thanks. And maybe just a little insight for those of you who, like me, might lack some of the smarts these other people have:

1. the main power wires to the pumps and what to do with them. Every post says to just seal them up and put them away. Welp, my 1985 535i has what looks like two power lines and a ground wire going to the main pump. After straight up cutting off the eyelets, and sealing them off (and attempting to sell the old pump as cek said) and then the new groovy pump didn't work...well, this led to a lot of head scratching and confused looks...and then a lot of diagnosis. I finally figured out that the two power lines at the main pump actually have to be connected. Although the pumps are wired in parallel, the main line from the fuse box hits the main pump AND splits to the aux pump. So when you do "tie them off", make sure to solder the apparently two power wires (green/purple in my case) together and seal them up. and cap off that ground like everyone says as well. Don't connect that to anything.

2. the tricky hose-in-hose line reducer for me, at the fuel filter, didn't work. Leaked like crazy. So I'm doing the barbed reducer from the big line to the small line into the fuel filter to fix that weak point.

There you have it, FWIW. Again - thanks to you all for this great discussion. It's been an awesome resource I have read through over and over again just to make sure I got it right. Seems to be working great now! I'm a recent graduate to the E28, but not new to BMW, and I'm really excited to jump in and do some of these restomods to make it a great machine again.

[Galahad]

1. the main power wires to the pumps and what to do with them. Every post says to just seal them up and put them away. Welp, my 1985 535i has what looks like two power lines and a ground wire going to the main pump. After straight up cutting off the eyelets, and sealing them off (and attempting to sell the old pump as cek said) and then the new groovy pump didn't work...well, this led to a lot of head scratching and confused looks...and then a lot of diagnosis. I finally figured out that the two power lines at the main pump actually have to be connected. Although the pumps are wired in parallel, the main line from the fuse box hits the main pump AND splits to the aux pump. So when you do "tie them off", make sure to solder the apparently two power wires (green/purple in my case) together and seal them up. and cap off that ground like everyone says as well. Don't connect that to anything.

For anyone reading in the future, an alternative to this is not cutting off the eyelets. I used heat shrink to cover mine so they didn't short to anything

[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!