BurgerMotorSports JB4. Detailed installation, thoughts, flex fuel help

So I finally upgraded to a full JB4 on my 335i. I picked one up from a forum member who was selling the latest JB4 model, bluetooth connect kit, and aluminum enclosure. The one caveat was it was missing the flex fuel wires. By missing, the seller meant the leads were cut off on the JB4 side of things… This guide is very similar to BMS’ official install guide but with some more details added.

Technical Skill
Time Commitment
PITA factor
Butt Dyno affect


Tools needed:

  • 10mm nut driver (seriously do yourself a favor. If you don’t have a decent set of nut drivers pickup a set of these Wera’s, the ergonomics and quality are hard to beat.)
  • Metal coat hanger/fish tape/fish stick/whatever
  • Zip ties
  • T50 Torx (optional, I bought this one)

The installation is pretty straight forward until you get to the flex fuel wires. Getting to the flex fuel wires is very difficult unless you remove the drivers side cowl. If you are not installing flex fuel wires the installation is a breeze, like 15 minutes tops. If you are installing flex fuel wires it will take a little longer.

  1. Disconnect the positive or negative battery cable in the trunk using your 10mm nut driver
    • I always remove the positive terminal in the trunk as it is possible to ground out the positive side easily under your hood
  2. Remove the engine cover by pulling up on it.
  3. Remove the passenger and drivers side cowl cover using your 10mm nut driver
    • Remove the cowl covers by turning the 3 (on each side) plastic nuts counter clockwise 90 degrees 
  4. If you are NOT INSTALLING FLEX FUEL WIRES, skip to step 7
  5. Only do this if you are installing Flex Fuel wires! Remove the cable running down through the rubber grommet going across the cowl cover:
  6. Remove the rubber seal
  7. At this point you should be able to pull the engine top foam off without tearing it and you should have access to the flex fuel connector. Below is a picture with the rough areas for each pigtail connection, connect each of the 3 or 4 pigtails depending on if you have a PWG or EWG car
  8. Now inside the car under the steering wheel remove the 2 10mm bolts holding the bottom cover on. (Picture coming soon)
  9. Now under the hood on the drivers side you will see a small firewall plug that can be pushed through, it will fall down by the pedals. Insert your fish (coat hanger, whatever you use through this hole), loosely tape the small 4 pin connector to it and pull it up into the engine bay.
  10. Connect the 4 pin connector coming through the firewall to the 4 pin female connector on the JB4 and the OBD2 control part is done.
  11. Coming out of the JB4 box should be a red and black wire
    1. If you have a T50 torx connect the red wire to the positive post (where you would jump start the car) on the passengers side.
    2. If you do not have a T50 Torx see here for an alternate location
      Alternate location, no T50 Torx

      3. For the ground wire I choose to use this location near the hood release mechanism, any bare metal will do

      Where I grounded the JB4
  12. Using your zipties mount the JB4 in an area of your choice, I found the area suggested by BMS to be pretty solid although having the aluminum chassis I was a bit worried about it sliding over and touching the battery jump start post. I opted to insulate the box with some black tape just in case.
  13. Reconnect your positive battery cable, install your engine foam, cowl covers, etc… and you should be good to go. Visit the n54 tech forums, update to the latest firmware, ensure all settings are set to default and enjoy.
  14. I suggest logging a few runs and posting them up to n54tech’s support forums to ensure everything is running smooth and setup correctly.


Flex Fuel Wire help

Here is the link to BMS’ official install instructions: http://www.burgertuning.com/instructions/N55_FlexFuel_Install.pdf

On the used JB4 I purchased the flex fuel wires coming from the JB4 box were completely cut off. On BMS’ install guide they mention something about a green wire pair that needs to be isolated and cut. These are old instructions for the old JB4 revisions, the newer JB4 revisions come with the flex fuel wires and they are not green, they are black. Here is my forum post for reference: http://www.n54tech.com/forums/showthread.php?t=43979


In case anyone else comes across this issue with cut JB4 flex fuel wires or missing flex fuel wires here is what you need to do in order to install a new flex fuel wiring harness.


  1. When you order new flex fuel wires from BMS They will come with a gold colored “pinned” end and a stripped end as seen in this picture:

    Pinned and stripped end on new flex fuel harness.
  2. Starting on Step 8 of BMS’ official install doc linked above, open up the JB4 unit, and remove the AMP shell connector.
    • Pay particular attention to the small screws you will be removing, you really don’t want to loose one of them…
  3. The “pinned” wire goes into position 21 on the pinout below and the stripped wire goes into position 4 on the picture below…

2 comments Add yours
  1. Does the stripped wire just go in like that without a pin ? Thanks for this post it helped me immensely

  2. Hi! Thank you for this post as it has been the only thing I’ve come across to shed any clarity on the Flex Fuel connector addon. The Flex fuel connecter I received are both “pinned” so I cannot differentiate which wire goes to which pin? Any advice?

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