How do I replace the crank angle sensor on a Mazda RX-7 FD?

Difficulty: Moderate Safety Warning: Disconnect the negative battery terminal before beginning work to prevent electrical shorts.

Replacing the crank angle sensors (CAS) on an FD RX-7 is a fairly straightforward mechanical process, though you will need to remove some accessories to access them.

Before you begin, note that actual CAS failures on the FD are extremely rare. Symptoms like a shaking idle, smoke, or bogging under acceleration are often misdiagnosed as a faulty CAS, but are more commonly caused by a disconnected MAP/boost sensor vacuum hose, bad ignition coils, or a break in the CAS wiring harness ⁵. It is highly recommended to check your wiring continuity to the ECU before replacing the sensors.

If you have confirmed the sensors need replacement or the sensor faces are physically damaged, here is the procedure:

Removal Procedure

1. Disconnect the negative battery terminal ⁵.
2. Remove both drive belts ⁵.
3. Remove the idler pulley assembly to gain clear access ⁵.
4. Remove the eccentric shaft (E-shaft) pulleys and the trigger ring. Do not remove the large E-shaft center bolt. The pulleys will come off by simply removing the four 6mm bolts and the E-shaft lock plate ⁵.
5. Disconnect the two electrical connectors for the sensors. Be sure to mark which connector goes to which sensor, as the plugs are typically color-coded differently (e.g., grey and white on a '94 harness) ⁵.
6. Remove the two 6mm bolts holding the sensors in place and pull the sensors free ⁵.

Reassembly

1. Install the new sensors and secure them with the 6mm bolts.
2. Reinstall the trigger ring and pulleys. Ensure the trigger wheel is correctly seated on its alignment pins and the pulleys are flush over their pins before tightening the four 6mm bolts ⁵. The stock FD trigger wheel will only line up in one correct position ¹.
3. Reconnect the colored electrical connectors to their proper sensors.
4. Reinstall the idler pulley assembly and drive belts.
5. Reconnect the battery.

Once the engine is running, always verify your ignition timing with a timing light to ensure the computer is getting an accurate reading from the trigger wheel ¹.