How To MegaSquirt Your Fox Body Mustang 5.0 (1986-1993)

• 1 MegaSquirt ECU
• 6ft of Back Hose
• Small Plastic T-Fitting
• 6ft Serial Cable
• 26 Pin Connector w/26 Leads
• USB Thumb Drive w/Tuner Studio
• Optional Equipment: Serial To USB Cable And Supported Wideband Gauges

Also note that the only item that is required for the installation is a modern laptop running a Windows OS. This MegaSquirt will fit 86’-93’ 302 or 351 based Mustangs. Also be aware that these instructions are for the current update and over time steps and processes can be changed with a software update from the developers.

1. Put vehicle on jack stands or a lift and disconnect the negative battery cable.
2. Since you will be working under the dash, we recommend removing both front seats to give you more work room.
3. On the passenger side of the car remove the frontward scuff plate retaining screw followed by the kick panel push pin.


4. Pass the kick panel over the scuff plate and pull straight out on the panel to remove from vehicle.


5. Locate the factory PCM and it may be in your best interest to disconnect a few electrical connections.


6. Loosen the 10 mm bolt that secures the electrical connection to the EEC. Once the bolt is loose, disconnect the connection.


7. Loosen and remove the 9/32” EEC cradle hold down bolt and slide the EEC out of the cradle and remove from car.


8. Loosen and remove the (2) 7mm glove box hinge retaining screws and open the glove box and squeeze both sides together so that you are able to remove it.


9. To remove the AC blower box, you will need to loosen and remove the upper bolt that is just behind the vent tube.


10. Loosen and remove the small 7 mm retaining screws located directly underneath the box.


11. Before dropping it dislodge the vacuum line and whenever you lower the box dislodge the electrical connection and it’s able to come out of the vehicle.


12. Dislodge the push pin that secures the sound deadening material and remove from vehicle


13. Remove the factory EEC cradle and set aside. (The reasoning for removing all of these pieces is to expose the passenger side firewall grommet)


14. Be careful to cut a small slit on the inside and outside of the grommet.


15. Tape the provided vacuum hose to a long ¼” extension and carefully push it through the open slit from the last step.


16. Once it comes out of the opening you can remove the tape and make sure about 2 ft of the hose is inside the car. (NOTE: use caution when pulling the hose through the grommet)
17. If you are installing a wideband into the car use this time to cut small openings into the driver side firewall grommet. These cuts will need to be a little large than the passenger side because it will have to pass through an electrical connector.
18. Tape the end of the wideband connector to the ¼” extension and feed through the opening like you did on the passenger side.
19. Disconnect whichever oxygen sensor you may be replacing with the wideband sensor. (Note: in this video we are replacing the driver side)


20. Loosen the sensor with a 7/8” wrench and remove from the midpipe.


21. Take the wideband sensor and apply anti-seize if needed.
22. Loosely tighten the new sensor because it will have to be removed again to properly calibrate.
23. Feed the new wire alongside the existing harness.


24. Tape the factory connector and secure it out of the way.


25. Secure the wideband sensor wire alongside the existing starter wire and tuck out of the way.


26. The PCM will need to be opened to configure the pre-installed oxygen sensor jumper and comes easily apart by removing the 4 phillips head screws and 2 hexagonal screws from the serial connection with a 5 mm socket.
27. Now that the top cover is removed, the only jumper that should be changed is J6 and controls the oxygen sensor connectivity.


28. With this jumper is also the pin labeled J8-29 and controls the passenger side bank, but since we are dealing with the driver side in this video, we are removing the jumper labeled J8-43.
29. Reassemble the PCM and carefully tighten the retaining hardware.
30. The wideband of choice in this video is an innovate wideband which means we will need to configure the provided 26 pin connector.
31. The oxygen sensor input connection is located on pin 21 on the connector.


32. The lead will install on the side with the larger holes and exit on the side with the smaller holes.


33. Position the 2 covers around the connector and use the small hexagonal nuts and small screws to secure the covers as well as the wire holder to fill the remaining hole.
34. Install the connector into the main port on the PCM.


35. Use the small flat rectangular washers and screws to secure the 26-pin connector to the PCM.


36. While the PCM is out of the car you will need to strip the wire.


37. The PCM cradle requires modification to fit the MegaSquirt and is done so by using 2 pieces of foam tape to prevent metal to metal contact and reduce rattle noise.


38. Plug in the factory connector and tighten the 10mm retaining bolt.


39. Connect the provided serial cable to the PCM and tighten the thumb screw.


40. Install the provided vacuum hose over the plastic barbed fitting.


41. Position the PCM in the original location and reconnect any electrical connections that were disconnected for extra working space.
42. Tuck the connections into the body of the car.


43. Pull any slack out of the vacuum hose and route it alongside the existing wiring harness. (Note: make sure the vacuum hose isn’t pinched)


44. Since there is a Vortech supercharger in this install we had to tap into an existing vacuum line that was previously ran.


45. Wrap the serial cable behind the dash towards whichever side you are working on and safely secure this cable to an existing wiring harness.


46. On the PCM remove the harness clip from the relay and position out of the way.


47. On this car we are using a pillar pod so we took the time to organize the wiring and temporarily mounted the pod to the car.


48. Next we ran the extended analog output wire from the wideband gauge towards the PCM.


49. Secure the wire to any existing harness that runs the length of the dash.
50. Slide a butt connector over the wire from the 26-pin connector and crimp it.


51. Route the wire from the wideband towards the butt connector and cut to length.


52. Strip the wire and twist.
53. Insert into the butt connector and crimp. Tuck out of the way. (If needed you can add heat to seal)


54. Also, since the MegaSquirt ECU uses speed density as the primary fuel metering method, a mass air flow meter is no longer required and can be removed. (It is also in your best interest to cover the sensor connection and secure out of the way)
55. Depending on your specific application, you will need to source an appropriate flow tube to fill the void of the mass air meter.
56. Take this time to calibrate the wideband sensor and load the tuner studio program into your laptop.
57. Refer to our extensive video that explains everything about the tuning program on the computer.
58. Once you have a good grasp on tuning your vehicle you can start reinstalling the rest of the interior components.

That’s it! We hope that we could provide a very detailed tutorial on this long process that is easy to understand and follow. Check out our video as well!