Test 3 - Power Transistor Testing

Ignition System:

To test the Power Transistor assembly, located on the intake manifold, using an analog type circuit tester proceed as follows.


1. Disconnect the power transistor connector.
2. Connect a power supply of 1.5v (one dry cell) between power transistor terminals 4 (-) and 3 (+).
3. Check for continuity between terminals 9 (+) and 4 (-). There should be continuity.
4. Remove power from terminals 3 and 4.
5. Check for continuity between terminals 9 (+) and 4 (-). There should not be continuity.
6. Connect a power supply of 1.5v (one dry cell) between power transistor terminals 4 (-) and 2 (+).
7. Check for continuity between terminals 8 (+) and 4 (-). There should be continuity.
8. Remove power from terminals 2 and 4.
9. Check for continuity between terminals 8 (+) and 4 (-). There should not be continuity.
10. Connect a power supply of 1.5v (one dry cell) between power transistor terminals 4 (-) and 1 (+).
11. Check for continuity between terminals 7 (+) and 4 (-). There should be continuity.
12. Remove power from terminals 1 and 4.
13. Check for continuity between terminals 7 (+) and 4 (-). There should not be continuity.
14. If the Power Transistor assembly fails any of these tests, replace it.


OSCILLOSCOPE TEST

Power Transistor Control Signal Scope Pattern:

Power transistor control signal test.
1. Crank or run engine.
2. Connect the scope probe to connector terminals 7, 8, and 9 (one at a time) and compare each signal to the pattern shown. If no signal is present check for an open/short in the wiring between MPI computer and power transistor. If wiring is not good repair as necessary and retest. If wiring is good, check top dead center sensor.