Chart C-4B: Ignition System Check (Trooper 2.8L)
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Two wires are checked to ensure an open is not present in a spark plug wire. If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
- A spark indicates distributor cap or rotor problem.
- With ignition on and engine off, there should be battery voltage at module terminals "C" and "+". Low voltage indicates an open or a high resistance circuit from distributor to coil or ignition switch. If terminal "C" voltage was low, but terminal "+" voltage is 10 volts or more, circuit from terminal "C" to ignition coil or ignition coil primary winding is open.
- Checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off, so voltage will be low, but greater than one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage leaks through module (from the battery to the tachometer terminal).
- Applying 1.5-8 volts to module terminal "P" should turn on the module. The tachometer terminal voltage should drop to approximately 7-9 volts. This test determines whether the module or coil is faulty, or if the pick-up coil is not generating the proper signal to turn on the module. This test can be performed by using a DC battery with a rating of 1.5-8 volts. The use of the test light is mainly to allow the terminal "P" to be probed more easily. Some digital multimeters can also be used to trigger the module. The voltage in the ohm position can be checked by using a second meter or by checking the manufacturer's specification of the Scan tester being used.
- This should turn off the module and cause a spark. If no spark occurs, fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. A module tester could determine which is at fault.