The Alternative Performance Engineering (APE) X85 Flex Fuel Kit is a great way to increase horsepower and torque on your BMW S65 engine (E90, E91, E92, E93 M3) while having the flexibility of running a variable concentration of ethanol. Ethanol tuning once used to be a high-involvement solution to increase power because it required a dedicated tune and the engine was 100% reliant on running a fixed ethanol concentration that it was tuned for. That has changed with the aftermarket Flex Fuel solution, however the market is still in the “early adopter” stage of the product. Those of you that run or have run a Flex Fuel solution, you know how convenient it is to not be 100% reliant on a fixed amount of ethanol while still making substantial power.

We’ve done numerous reviews for the E46 M3 and now we are proud to have tested the same APE flex fuel kit for the V8 S65 engine. Below is a guide to do the install. It’s pretty straight forward.

APE X85 Flex Fuel Kit Installation

1. Remove fuse #70 (fuel pump) and start the car. Let the engine stall. This will remove excess fuel in the lines to help reduce the amount of fuel leaking out of the lines when you disconnect it in the later steps.

2. Disconnect battery harness to reduce any chances of electrical issues during the install.

3. Remove upper intake cover.

4. Remove lower half of intake box.

5. Locate the fuel line towards the back of the engine bay closest to the driver side firewall.

6. Locate the fuel line towards the back of the engine bay closest to the driver side firewall.

7. Disconnect main fuel line.

8. Assemble the flex fuel sensor unit and install in place of the original fuel line.

9. Grab the main wiring harness loop for the injectors and feed through each side of the engine. It’s going to get really tight and you may need to remove the top intake plenum to gain more clearance. In my case, I did not have to.

10. Start disconnecting all 8 Bosch EV1 connectors by pulling the metal tab up. This is going to be tricky and you will need a small pick to get to the metal tabs. Be careful not to pull out too much because you will dislodge the metal tab and may drop inside the engine bay.

On the driver side, disconnect the intake return inlet hose to make clearance.

11. Once all 8 connectors are plugged in, tuck in the wiring as best as you can. I used several zip ties to keep the wires together.

12. Mount the main module to a “cooler” area on the car. I decided to mount mine next to the passenger side firewall. Try to avoid mounting it close to the headers or anywhere that may get really hot.

Identify the passcode on the back of the module before you install as you will need that to access additional tuning features.

13. Connect the ground coming from the harness. There is a ground point right next to the washer fluid fill cap.

14. Reconnect the battery and start the car up. Run the engine for a bit and check for fuel leaks.

15. Once everything is good, re-install your intake.

16. Finally, download the APE ape from the app store and connect via Bluetooth.