How to Repair a '93 Miata's Camshaft Sensor

The 1993 Mazda Miata uses a combination camshaft and crankshaft sensor in one. It is called the crank angle sensor or camshaft interrupter magnet. To order the part, use the crank angle sensor terminology. The sensor is at the top rear of the cylinder head and is a round object, about 3.5 inches in diameter. Its purpose is to signal the location of the crankshaft relative to top dead center on the compression stroke. This information is used to regulate the fuel injection and ignition timing.

Instructions

Removal

1

Unplug the sensor wire connector from the sensor.

2

Match-mark the sensor housing and the cylinder head for alignment during installation. Remove the 12 mm bolt using a socket and ratchet.

3

Pull the sensor up and out of the engine.

Installation

4

Transcribe the match-mark in the same location on the new sensor for installation purposes and to preserve the current ignition timing. Apply a thin coat of oil on the O ring and the gear of the new sensor to ease installation.

5

Install the new sensor and align the match-mark made earlier with the one on the cylinder head. Install the 12 mm bolt and torque it to 14 to 20 foot-pounds. Plug the electrical harness wire connector into the sensor.

6

Check the ignition timing for accuracy. Remove the cap on the diagnostics connector on the driver-side fender close to the air intake duct. It's in plain sight. Look at the diagram illustrating the terminal numbering. You will jump between the ground and the No.10 terminals. Install the inductive timing light by connecting the black lead to a good ground. Connect the red power lead to the remote power terminal with the blue cap on the driver's fender well. Clamp the pickup on the No.1 spark plug wire, the one closest to the radiator. Lay the timing light so the wires do not get caught in the fan or any moving parts.

7

Place a white mark on the notch in the crankshaft pulley, which is the timing mark. Notice the timing indicator scale on the plastic timing cover. The lines represent 2-degree increments. Find the 10-degree BTDC -- before top dead center -- mark. Place a white mark at this position.

8

Start the engine and allow it to warm up to normal operating temperature. Insert a paper clip end or short piece of wire in the diagnostics connector ground terminal, and the other end in the No. 10 terminal. This will set the computer to base timing. Look at the tachometer and make sure the rpm is 850. If not, set the idle by turning the idle adjustment screw on the throttle body, using a flat-head screwdriver.

9

Point the timing light at the crankshaft pulley and notice the position of the white timing mark relative to the mark on the timing cover. If the marks are aligned, the timing is fine. If the marks do not align, use the 12 mm socket and loosen the hold-down bolt on the crank angle sensor. Rotate the sensor slightly until the two timing marks are in alignment. Tighten the bolt and re-torque it to specifications.

10

Shut the engine off and remove the timing light and the paper clip from the diagnostic connector.