BM3 Flex Fuel Kit – DIY Assembly Instructions

This guide walks through the BM3 Flex Fuel Kit assembly procedure. Those customers purchasing the BM3 Flex Fuel Kit can use this guide as a DIY manual for assembling their own kit when purchasing it without the GM/Continental Flex Fuel sensor included from us.

NOTE: We do not recommend this DIY as there are multiple steps involved in assembly and the procedure, while not very difficult, does require multiple tools, engine lube, teflon paste and is not very trivial.


Tools required for assembly:

  1. 3/16” Hex (Allen) Key

  2. 5/32” Hex (Allen) Key

  3. -6AN Wrench

  4. GM/Continental Flex Fuel Sensor, Part Numbers: 13507129, 13577429

    1. NOTE: Only the short-tube small housing version of this sensor can be assembled into our 3-piece machined sensor adapter. You cannot use the long tube version of it or the large housing 4-bolt version of it (picture below)

  5. Engine oil (any, to lube seals/fittings)

  6. Thread Sealant - fuel/oil/chemical safe

    1. We use: Permatex Part Number: 59206 (high temp, chemical (oil/fuel) safe, white teflon paste)

To begin assembly ensure you have all the parts of the BM3 Flex Fuel Kit as outlined in the picture below, here’s a listing:

  • (3) Machined black anodized pieces of the sensor adapter (one is labeled with BM3, top right of the picture)

  • (4) Viton seals (white)

  • (1) -6 ORB Male » -6 AN Male fitting with an E85 compatible seal (black)

  • (4) Hex screws (silver)

  • (2) 1/8 NPT plugs (bronze)

NOTE: You need to source an appropriate high temp chemical safe (fuel/oil/alcohol) thread sealant. We typically use the one from Permatex as outlined above and shown in the pic below.

To start assembly, take the 4 white Viton seals, apply a bit of engine lube on them to not cause a tear during installation, and install them as follows (see pic below):

  • 2 on the flex fuel sensor (one on each side of the tube)

  • 1 on the bm3 labeled machined sensor adapter part

  • 1 on the smaller machined sensor adapter part

Once the 4 Viton seals are set, apply thread sealant to each of the bronze 1/8 NPT plugs and install them onto the two sensor adapter pieces as follows:

Once the viton seals are on the sensor tubes and lubed, begin assembly of the flex fuel sensor into the sensor adapter housing. On the bm3 labeled side, push the tube inside the housing:

Here are a few more pictures of the final assembled adapter without the XRP hose on it: