Power Transistor & Ignition Coil
*** UPDATED BY TSB# 89-008-003 January, 1989Power Transistor And Coil:
To test the Power Transistor, located on the intake manifold, using an analog type circuit tester proceed as follows.
Component Test:
1. Disconnect the power transistor connector.
2. Connect a power supply of 1.5v (one dry cell) between power transistor terminals 2 (-) and 1 (+).
3. Check for continuity between terminals 3 (+) and 2 (-). There should be continuity.
4. Remove power from terminals 1 and 2.
5. Check for continuity between terminals 3 (+) and 2 (-). There should not be continuity.
If the Power Transistor fails any of these tests, replace the Power Transistor.
OSCILLOSCOPE TEST
Oscilloscope Pattern:
Power transistor control signal test.
1. Run engine at idle speed.
2. Connect the scope probe to pick-up point #2 shown in the system schematic diagram and compare the signal to the pattern shown. If scope pattern is not as depicted in image, continue with the rest of the test procedures before replacing the assembly.
HARNESS TEST
1. Disconnect the ignition coil connector and turn on the ignition.
2. Using a voltmeter, measure the power supply circuit of the ignition coil between the harness connector terminal 1 and ground.
Voltage: System Voltage.
3. Disconnect the power transistor connector. Check for continuity (shorts) to ground between the power transistor harness connector terminal 3 and ground and the ignition coil harness connector terminal 2 and ground.
Continuity: Should Not Exist.
4. Check for continuity between the power transistor harness connector terminal 3 and the ignition coil harness connector terminal 2.
Continuity: Should Exist.
5. Check for continuity of the ground circuit, between the power transistor harness connector terminal 2 and ground.
Continuity: Should Exist.
6. With the ignition switch in the start position, connect a voltmeter between the power transistor harness connector terminal 1 and ground and measure the voltage of the control signal circuit of the power transistor.
Voltage: 2 - 6 Volts.
7. With the ignition switch in the on position, connect a voltmeter between the ignition timing adjustment connector terminal 1 and ground. Measure the voltage of the ignition timing adjustment connector.
Voltage: 4.0 - 5.2 Volts.
If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, road test the vehicle to confirm that the repair has corrected the problem.
If the same problem reoccurs, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.