Engine Speed/Cylinder Reference Sensors

Note: All 1986 vechicles use two sensors in the bellhousing. For 1987 vehicles, two types of speed/reference sensors were available:

^ Two sensors in the bellhousing, or
^ One combined sensor at the vibration damper

Inspect the vehicle to determine which system is used, and test accordingly. Each car will have one type of sender or the other (not both).

The most accurate method of testing either type of sender is with an oscilloscope. If a sender is only slightly out of specification on the resistance test, but has a good scope pattern, the sender is probably OK. If, however, the resistance is within specification, but the scope pattern is bad, replace the sender.

Do not confuse the TDC sensor with the pulse transmitter. If there are no teeth on the crankshaft vibration damper, the sensor at the front of the engine is the TDC sensor.

Seperate Sensors

Fig. 65 Pulse transmitter plug:

The engine speed sensor and cylinder reference sensor are mounted in the transmission bellhousing. The speed sensor uses the teeth of the ring gear and the reference sensor uses steel dowels on the face of the flywheel for their respective signals. To test the transmitters:

1. Disconnect each sensors' plug.
2. Connect an oscilloscope to connections 1 and 2, Fig. 65, of the sender, and crank the engine. Scope pattern should look like:

Fig. 6 Speed transmitter scope pattern.:

Engine Speed Sensor -- Fig. 6.

Reference Sensor Scope Pattern:

Cylinder Reference Sensor -- Fig. 5.

3. Measure resistance between terminals 1 and 2 on each transmitter. Resistance should be 960 Ohms ± 10%
4. Replace either transmitter if it fails one of the tests.

Combined Sensor

Fig. 65 Pulse transmitter plug:

Fig. 67 Pulse transmitter scope pattern:

The pulse transmitter is mounted on the passenger side of the front of the engine (above the A/C compressor), and gets its signals from the teeth cast into the vibration damper. This transmitter performs a dual function, taking the place of the separate speed and reference sensors that were mounted in the bellhousing at the rear of the engine on other models. The speed signal comes from the teeth in the vibration damper, while the reference signal is derived from two specific missing teeth. To test the transmitter:

1. Disconnect pulse transmitter plug.
2. Connect an oscilloscope to connections 1 and 2 of the pulse sender, and crank the engine. Scope pattern should look like Fig. 67.
3. Measure resistance between terminals 1 and 2, Fig. 65. Resistance should be 540 Ohms ± 50 Ohms.
4. Replace the transmitter if it fails either test.