DIY - Double to Single Fuel Pump Conversion

[reelizmpro]

Thought I would update this thread since I am doing this again on my 85 323i. It's been a few years and all is well with the conversion on my M3. The shortened stock reducer hose has not split. Here are some pictures to show you what needs to be done.

Note the size of the outlet on the brass holder vs the new TRE fuel pump.


I installed the TRE pump high enough to where the outlet is practically inside the brass tube and the connection is secured with the shortened reducer hose and clamps. The height also keeps the pick up in the ideal location. Make sure you orientate the filter at the proper angle and the level sensor clears the pump as well. For power, I desoldered the stock wiring and soldered the new wiring to the + terminal. For the ground, I chose to install a ring terminal on the ground wire and used the factory ground screw to ground the new pump. Here it is all assembled next to the original.

[marsgorski]

transfer pump current draw

After a few days it doesn't appear to be leaking. All is well. I measured current draw at the pump as 6.47 amps. Using online calculators, 17 gauge can support 6.5 A upto 6ft or so. We just have to determine exactly how long that wiring is.

Edit, interestingly the ETM for 89 M3 shows that the main pump and transfer pump use the same 1.5mm square wiring.

I'm currently working on a problem my car has (described here) and I tried testing the current draw on my transfer pump. I got 0 amps, but I suspect I may have done something wrong. Can you describe the process by which you measured your? That would be greatly appreciated!

[mach schnell]

Is there a DIY on how to do this with factory BMW parts, including the later fuel pump setup?

[thejaredhuang]

My stock splitter split, what have others done when this happens? I was thinking of cutting out the stock hard line and putting in a 5/16 bulkhead connector but that seems like a lot of work to replace a 1" section of hose.

Edit: I measured the sizes of the hard line and my fuel pump. hardline is 12mm OD, slightly smaller than 1/2 this is the same for the assembly so the OP of 3/8 should be ignored. The outlet on my pump stock level OSIAS chinese pump is 10mm. I tested a 10mm ID fuel line hose and you can stretch it enough to fit onto the 12mm hardline so that's what I'm going to do. Make sure you use submersible hose as regular hose will deteriorate when submerged. The short hose that comes with most in tank pumps should be submersible rated.

PS I picked the OSIAS pump because it supposedly has carbon bushes and it comes with a lifetime warranty. For anyone wondering it drew 5.3A @ 12V and flows 155l/h. This is not their "340lph" pump, its the one that comes up as a stock replacement pump. I hardly drive the car though so it will take me years to give a long term review.

[5mall5nail5]

Sorry to bump as well, but I am having a no start issue and when I jump the fuel pump relay on my 24v swap (which ran previously) I hear NO fuel pump noise at either the in-tank pump nor external. It's possible my car has been driving around on one or the other because I rarely drive it and did have issues with the original M20. That said, I heard that the fuel line coming off of the fuel tank sender and into the external pump is not rated for fuel injection - it apparently can't handle high PSI? Is that true? And, if so, is it somewhat easy to run a replacement line without dropping the fuel tank?

Thanks!

[reelizmpro]

The only weak link is that short reducer pump-to-carrier hose. Solve that problem and the rest works fine.

[thejaredhuang]

Sorry to bump as well, but I am having a no start issue and when I jump the fuel pump relay on my 24v swap (which ran previously) I hear NO fuel pump noise at either the in-tank pump nor external. It's possible my car has been driving around on one or the other because I rarely drive it and did have issues with the original M20. That said, I heard that the fuel line coming off of the fuel tank sender and into the external pump is not rated for fuel injection - it apparently can't handle high PSI? Is that true? And, if so, is it somewhat easy to run a replacement line without dropping the fuel tank?

Thanks!

Late response but I had the same issue after i swapped pumps. I didn't flare the hardline and the rubber hose + clamp I used slipped off.

The line coming from the sender to the external is probably not FI rated, I replaced mine when my short rubber hose burst so I'm not sure if it was going to fail or not. I just taped my new line to the old one and pulled the old line out from the bottom of the car, it dragged the new line with it. You need about 3ft of line.

[LBC28730]

Outstanding. Thank you so much for this.

[LBC28730]

Just got the TRE to replace both pumps on my 87is.

Originally I pulled the assembly off an 84 I just got, thinking I would leisurely do it and then swap but it was SUPER nasty and the 10y of sitting did not do good for it.

I measured from the top of the case to the bottom of the filter and ended up with a difference of about 20mm.

I removed 20mm from the main output tube (hand saw is easy to cut this, you don't want to use power tools as this is still fuel related and it's an unnecessary risk) and attached with clamps (I don't know what they are called but they are the OE style crimp clamps for fuel lines, I got a kit on Amazon pretty cheap), one was 17mm the other was 22mm.

Soldered and shrink wrapped the red line to the black from the assembly. I was thinking about desoldering the line from the connection on the assembly and just running the red wire to that but was wanting to get it done so I just did as mentioned. I did notice that the wire from the TRE pump was slightly heavier gauge so if someone is worried about delivery, desoldering the connection and just running it straight to it would not be hard at all.
My car is totally stock and this one will remain that way so I am not too concerned.

Instead of soldering the black wire to the feed line as shown here, I used the ground point that was already available, where the original pump grounded to.
This seemed to simplify things for me a bit as then you don't have to worry about the quality of your solder to the tube. That tube is good sized and a major heatsink. If it's not pretty clean and soldered just right, it may not stick.

I crimped a small eye on the black wire, shrink wrapped it, and attached it with the original clip and screw that held the ground for the original pump and it is putting out fuel great.

As for the fuel pump "blanking", I bought a 1/2x5/16 brass barbed reducer off Amazon for $6. I was familiar with these when I did fuel system retrofit/upgrade on my 83 Westy and needed something similar. If you are in a hurry and need it literally right now; you can piece it together but in the long run, one solid piece is going to be much better/safer.

[LBC28730]

Unfortunately this pump has already failed.

Spent far too long chasing a 1222 fault code (I converted to MT 1.3 specifically for code storing) and finally tested fuel pressure. 18psi..

I got it from TRE and it has a 1 year replacement.

Called just now and they said just reply to order confirmation email and they'll get the replacement set up.

So far seems to be a smooth transaction, let's hope the replacement lasts a bit longer.

[LBC28730]

Replacement has failed as well, only putting out 21psi.....and again, after spending a LONG time chasing that 1222, again........

Just ordered the OSAIS 340lph...

[reelizmpro]

Sorry you are having trouble with the TRE's. Having two pumps in a row fail, isn't a good look.

[LBC28730]

Sorry you are having trouble with the TRE's. Having two pumps in a row fail, isn't a good look.

I should comment for posterity on this thread: my current issue was NOT due to the TRE pump failure. Turns out I had one small section of hose that was beginning to fail internally, much like soft brake lines do.
I've now replaced all soft hoses as well as blew out the hard lines with compressed air, and everything is working as it should.

After going through the troubleshooting as with the first pump, I was able to determine that it was not the pump, this time.

First pump was bad but TRE was really great with support and supplying a replacement in a very timely manner.