How To Megasquirt Your 2nd Gen RX-7: Remove Stock Wiring and ECU

Now it's time to start working on the actual car. First, we need to remove the upper intake manifold to access the injector connections. Then the stock EFI harness gets disconnected from the engine. After that, the ECU is removed from the car and the harness pulled through the firewall. Finally, a portion of the old harness needs to be cut free and reinstalled on the car to maintain the windshield wiper function (and a few others, depending on the car). Not every step is going to be covered in detail because some are already in the factory service and Haynes manuals.

Remove The Upper Intake Manifold

Using instructions in the Haynes manual or Factory Service Manual, remove the upper intake manifold. If you are referencing the Haynes, you will find these instructions in chapter 2, part A. The emissions and fuel diagrams in chapters 4 and 6 will also be of great help. In the FSM, you will find manifold removal instructions in section 4. 4A covers NA, 4B covers TII. If this is the first time you have removed the manifolds, label all connections and hoses. Take plenty of pictures and keep things in order.

With the manifold removed, put it aside in a safe place and continue on with the next step.

Remove Wiring Harness and ECU

Next to go is the stock wiring harness and ECU. The harness we are dealing with is technically called the "emissions harness" (EM) in the factory and Haynes service manuals. It is the harness which connects from the ECU to the engine and all EFI hardware. Often called the "EFI" harness, it will be referred to here as the emissions or EFI harness. Note that the "engine" harness is a different animal entirely (it connects to the starter).

Disconnect the EFI harness from all of the engine sensors. Most of these were already disconnected when you removed the upper intake manifold. Remember that the harness connects to the AFM, variable resistor, pressure/boost sensor, solenoid resistor (if present) and oddly, the wiper motor. Once the harness is disconnected, you can drape it over the side of the car and let it dangle.

Inside the car, remove the screws holding on the door sill and then remove the sill. It is clipped on as well as screwed so it will take some effort. Now remove the passenger kick panel trim. It is secured with fir-tree fasteners that get pried out with needle nosed pliers or the special tool for this purpose. Pull back the carpet to expose the ECU cover, and remove it after unbolting the 4 10MM bolts.

Now the ECU is exposed so disconnect the harness connectors from it. Depending on what year your car is and whether it is turbo or NA, there may be a few other connections in that area. Remove them as well. Unbolt the ECU bracket from the car and remove it with the ECU attached. To the right of the ECU, inside the passenger kick panel is a large orange connector where the EFI harness meets the body harness. Disconnect it. If the knock retard box is present (TIIs only), it will need to be removed (it can be set aside) first. Disconnect the atmospheric pressure sensor, remove the sensor, and set it aside.

Working from the outside of the car, compress the rubber grommet of the EFI harness while working your fingers around its edges. Generally if you push in the top and then pull, it will come free. With the grommet freed, slowly draw the harness through making sure to go back in the car and clear any snags or connectors you may have forgotten.

Set the harness aside. We'll come back to it later. At this point, all of the stock EFI electronics have been removed from the car. You may want to take this opportunity to remove all the extra harness and sensor brackets no longer needed. For example, the variable resistor, solenoid resistor, pressure sensor, etc. We won't be needed anything from that side of the engine bay.

Remove The AFM

Here's where you have some decisions to make and where some creativity needs to be exercised.

The AFM is no longer needed or wanted, but it can't just be removed. If you have a fully stock car, then the AFM is what connects the intake tube (or TID, for turbo cars) to the airbox. If you have an aftermarket intake kit and a stock ECU (which you almost certainly do if you are reading this) then you will still have an AFM but some kind of adapter will be used to connect it to a cone filter. You need to figure out a way to remove the AFM from the intake tract, and then install an air filter in its place.

Unfortunately this is a sad gap in the aftermarket products for RX-7s. At the moment there are no commercially available intake kits, let alone one designed for a standalone installation. TII owners can make a TID using common ABS plastic pipes. Searching the RX-7 Forum will turn up some instructions (try keywords like "tid", "turbo inlet duct"). If you are NA, it may be worthwhile to just buy an air filter that has a 3 1/2" clamping surface so you can just clamp it directly to the intake tube. If you are going to get fancy, pick up some aluminum tubing bends, silicone couplers and build a new intake setup. Try searching the RX-7 forum for "prelude intake" for some clues on how to proceed.

If you are just ultimately concerned with getting the Megasquirt running, leave the AFM alone and use the stock intake setup. The AFM will do no harm simply being there and you can remove it later on when you figure out what to do.

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