First, a word of warning:
I did this on a pre-9/1987 325i convertible and everything I post is applicable to how I did it on MY car. Your car may be different. It is YOUR responsibility to look up the Electrical Troubleshooting Manual (ETM) for YOUR car so YOU can verify how it was wired.
BMW ETMs
Next, you are working with gasoline and electricity. It can be very dangerous if you’re not careful. Although there should be too much fuel to not enough oxygen for a spark in the gas tank to ignite fuel vapors, this is still a possibility because you are modifying electrical connections.
Finally, do not attempt this if you feel uncomfortable performing this modification. Read the entire write-up before starting and make sure you have the appropriate tools.
Parts required:
-TRE-340 (comes with fuel pump, fuel filter, fuel line, 2 hose clamps, long fuel line, electrical plug, insulation, and rubber cap)
-3/8 in barbed fuel nipple (a slightly larger size would be better, preferably 1/2 inch since the larger line is 13mm ID)
-5/16 in barbed fuel nipple
-Union to connect the two nipples
-Teflon tape (for pipe threads)
-Heat shrink cable wrap
-extra hose clamps as needed
Tools required:
-Philips head screwdriver
-Flat head screwdriver
-10 mm socket
-8 mm socket
-socket wrench
-wire cutter
-wire stripper
-multi-meter
-lighter
-soldering gun and solder
-sand paper
Initial steps not covered:
Remove the in-tank pump, the fuel filter, the external pump, and the mounting bracket for the external pump/fuel filter.
How to convert:
Here is an image showing the fuel system from the ETM for my car. It shows that both fuel pumps are fed by a common wire. It also shows that the wire to the external pump has a diameter 2.5 times larger than the diameter of the wire going to the in-tank pump. I am assuming that the wire going to the single in-tank pump will be capable of providing enough electricity without overloading and/or shorting. I intend to cap off the wires for the external pump and use the in-tank pump wires to power the new TRE pump.
Once you have the in-tank pump out, bring it to your work bench. Notice that the BLACK wire goes to the positive terminal on the pump and the negative terminal grounds to the part holding the pump. The unit will look all rusty like this:
I’ve cleaned the holder and set the pump next to the holder in the approximate spot where it would be attached. Notice that the strainer is roughly 0.5 cm below the bottom of the metal return fuel line. This is the location you want the new pump filter so you don’t experience fuel starvation in corners or “run out of gas” when there is still fuel in the tank.
Here are the contents of the TRE-340 fuel pump kit:
The fuel line supplied with the pump easily won’t fit over solid line, so I re-used the old reducer. Here is pump mocked up with the old reducer. Notice that the pump extends roughly 2.5 cm past the return hardline. It is too long when positioned like this and will hit the bottom of the fuel tank before you can tighten the pump unit. Make sure you visually inspect the reducer for cracks. My reducer split down the side one day as I got to work. It was a huge pain in the ass to limp it home, but I eventually made it. I spent about 10 minutes looking for a part number for the reducer, but it looks like it only comes as part of the fuel pump assembly. It is possible to heat and stretch the opaque plastic tube that comes with the TRE pump to make it fit on both the metal hardline and the pump. (It's just not the best option.)
I have cut the solid line so that the top of the old reducer is right at the bend. You can see that the bottom of the fuel pump is now in roughly the same location as the stock strainer:
Now slip a piece of heat shrink cable insulation over the ling RED wire for the fuel pump plug. Then solder the end of the RED wire to the BLACK wire on the pump holder.
Pull the heat shrink over it and shrink it:
Now solder the BLACK wire to the pump holder return hard line. This is a good time to test for continuity. First test the positive wire from the car side plug to the pump side plug, then repeat for the negative wire. Next, plug in the pump and test for continuity from the positive to negative terminals on the car side plug. If everything is soldered correctly you should be good to move on to the next step.
I zip-tied the black wire into place so it couldn’t move and break the solder joint. Then I put the insulation over the pump and slid the black rubber bottom piece on. I’m not sure either of these are needed, but the insulation makes it easier to hold the pump to the metal unit. Then I used the supplied hose clamps to tighten the old fuel hose reducer to both the metal unit and the pump. At this point the pump should not be able to fall off, however, it would still shake around. So I used metal zip-ties to secure the pump to the return line. I tried using a hose clamp, but the hole in the gas tank is too small to accommodate the pump and a hose clamp. I considered using plastic hose clamps for this, but was concerned about them degrading in the fuel. Finally, I plugged in the pump and zip-tied the extra wire length to the metal holder. Make sure you do this so it will be out of the way of the fuel level sending unit!.
Once the in-tank pump is installed, it’s time to by-pass the external pump. Take some heat shrink cable wrap and cover the wires that power the pump. Then push them up into their protective covering. This step ensures that you won’t have a short because unused connectors are dangling against the car. (I would suggest not cutting them in case you or the next owner wants to revert back to the original setup.)
These are the pieces I got from Advance Auto. The 3/8 in fuel line nipple is a little smaller than the stock 13 mm diameter large fuel line by roughly 3.475 mm, which is why I would suggest finding a 1/2 in nipple (1/2 in = 12.7 mm). The 5/16 in fuel line nipple is basically a perfect fit. Make sure you wrap the threads with Teflon tape and then tighten them together.
Next, take the mount that held the external fuel pump bolt it back into the car. Run the large fuel line through the opening for the external fuel pump and connect the line that will go to the fuel filter. I suggest zip-ting the electrical connectors from the external pump to the mount that held the external fuel pump so they don’t flop around.
Make sure the large hose clamps are in over the fuel line so you can hang the fuel filter, then connect the fuel lines to both sides of the fuel filter. Finally, hang the fuel filter and replace any trim bits.
I did this on a pre-9/1987 325i convertible and everything I post is applicable to how I did it on MY car. Your car may be different. It is YOUR responsibility to look up the Electrical Troubleshooting Manual (ETM) for YOUR car so YOU can verify how it was wired.
BMW ETMs
Next, you are working with gasoline and electricity. It can be very dangerous if you’re not careful. Although there should be too much fuel to not enough oxygen for a spark in the gas tank to ignite fuel vapors, this is still a possibility because you are modifying electrical connections.
Finally, do not attempt this if you feel uncomfortable performing this modification. Read the entire write-up before starting and make sure you have the appropriate tools.
Parts required:
-TRE-340 (comes with fuel pump, fuel filter, fuel line, 2 hose clamps, long fuel line, electrical plug, insulation, and rubber cap)
-3/8 in barbed fuel nipple (a slightly larger size would be better, preferably 1/2 inch since the larger line is 13mm ID)
-5/16 in barbed fuel nipple
-Union to connect the two nipples
-Teflon tape (for pipe threads)
-Heat shrink cable wrap
-extra hose clamps as needed
Tools required:
-Philips head screwdriver
-Flat head screwdriver
-10 mm socket
-8 mm socket
-socket wrench
-wire cutter
-wire stripper
-multi-meter
-lighter
-soldering gun and solder
-sand paper
Initial steps not covered:
Remove the in-tank pump, the fuel filter, the external pump, and the mounting bracket for the external pump/fuel filter.
How to convert:
Here is an image showing the fuel system from the ETM for my car. It shows that both fuel pumps are fed by a common wire. It also shows that the wire to the external pump has a diameter 2.5 times larger than the diameter of the wire going to the in-tank pump. I am assuming that the wire going to the single in-tank pump will be capable of providing enough electricity without overloading and/or shorting. I intend to cap off the wires for the external pump and use the in-tank pump wires to power the new TRE pump.
Once you have the in-tank pump out, bring it to your work bench. Notice that the BLACK wire goes to the positive terminal on the pump and the negative terminal grounds to the part holding the pump. The unit will look all rusty like this:
I’ve cleaned the holder and set the pump next to the holder in the approximate spot where it would be attached. Notice that the strainer is roughly 0.5 cm below the bottom of the metal return fuel line. This is the location you want the new pump filter so you don’t experience fuel starvation in corners or “run out of gas” when there is still fuel in the tank.
Here are the contents of the TRE-340 fuel pump kit:
The fuel line supplied with the pump easily won’t fit over solid line, so I re-used the old reducer. Here is pump mocked up with the old reducer. Notice that the pump extends roughly 2.5 cm past the return hardline. It is too long when positioned like this and will hit the bottom of the fuel tank before you can tighten the pump unit. Make sure you visually inspect the reducer for cracks. My reducer split down the side one day as I got to work. It was a huge pain in the ass to limp it home, but I eventually made it. I spent about 10 minutes looking for a part number for the reducer, but it looks like it only comes as part of the fuel pump assembly. It is possible to heat and stretch the opaque plastic tube that comes with the TRE pump to make it fit on both the metal hardline and the pump. (It's just not the best option.)
I have cut the solid line so that the top of the old reducer is right at the bend. You can see that the bottom of the fuel pump is now in roughly the same location as the stock strainer:
Now slip a piece of heat shrink cable insulation over the ling RED wire for the fuel pump plug. Then solder the end of the RED wire to the BLACK wire on the pump holder.
Pull the heat shrink over it and shrink it:
Now solder the BLACK wire to the pump holder return hard line. This is a good time to test for continuity. First test the positive wire from the car side plug to the pump side plug, then repeat for the negative wire. Next, plug in the pump and test for continuity from the positive to negative terminals on the car side plug. If everything is soldered correctly you should be good to move on to the next step.
I zip-tied the black wire into place so it couldn’t move and break the solder joint. Then I put the insulation over the pump and slid the black rubber bottom piece on. I’m not sure either of these are needed, but the insulation makes it easier to hold the pump to the metal unit. Then I used the supplied hose clamps to tighten the old fuel hose reducer to both the metal unit and the pump. At this point the pump should not be able to fall off, however, it would still shake around. So I used metal zip-ties to secure the pump to the return line. I tried using a hose clamp, but the hole in the gas tank is too small to accommodate the pump and a hose clamp. I considered using plastic hose clamps for this, but was concerned about them degrading in the fuel. Finally, I plugged in the pump and zip-tied the extra wire length to the metal holder. Make sure you do this so it will be out of the way of the fuel level sending unit!.
Once the in-tank pump is installed, it’s time to by-pass the external pump. Take some heat shrink cable wrap and cover the wires that power the pump. Then push them up into their protective covering. This step ensures that you won’t have a short because unused connectors are dangling against the car. (I would suggest not cutting them in case you or the next owner wants to revert back to the original setup.)
These are the pieces I got from Advance Auto. The 3/8 in fuel line nipple is a little smaller than the stock 13 mm diameter large fuel line by roughly 3.475 mm, which is why I would suggest finding a 1/2 in nipple (1/2 in = 12.7 mm). The 5/16 in fuel line nipple is basically a perfect fit. Make sure you wrap the threads with Teflon tape and then tighten them together.
Next, take the mount that held the external fuel pump bolt it back into the car. Run the large fuel line through the opening for the external fuel pump and connect the line that will go to the fuel filter. I suggest zip-ting the electrical connectors from the external pump to the mount that held the external fuel pump so they don’t flop around.
Make sure the large hose clamps are in over the fuel line so you can hang the fuel filter, then connect the fuel lines to both sides of the fuel filter. Finally, hang the fuel filter and replace any trim bits.
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