NA Miata - Symptoms of a bad CAS
Channel: AmbiVe
Date: 2021-05-19

In this video, I give a brief summary of the symptoms and diagnostics involved in identifying a bad CAS on my girlfriend's 1992 Mazda Miata. The NA Miata Cam Angle Sensor or Crank Angle Sensor is the large round unit at the back of the valve cover on the passenger side. It is engaged with the intake cam and provides information to the computer system to allow the proper timing of fuel injection and spark. As this system began to fail, the car would stumble/hesitate, violently jerk, and stall. Initially very occasional, it eventually became a nearly constant issue.

Replacing the CAS is relatively easy. Mark the orientation of the CAS, make a mark on the body of the CAS as well as the head of the car. You will need to use this to align the new unit in the same position. Remove the old CAS from the rear of the engine by removing the single 12mm bolt and unplugging it. Apply equal pressure toward the firewall to slip the large o-ring that surrounds it out of place. Once free, make note of the orientation of the engagement shaft to the cam. It has a directional key, you need to know what side the notched/slopped side of the key was pointing. Turn the new CAS key to the same orientation and begin fiddling with getting it slipped into place. I would suggest lubricating the o-ring to make installation easier and reduce the chance of damaging the ring. This is a common oil leak on NA Miatas. If the keyed shaft is aligned correctly, the unit should slip into place.