Primary and Secondary Ignition Inspection
CONDITIONS OF IGNITION SYSTEM FAILUREIf the 24X reference signal is not received by the PCM while the engine is running, a DTC P0336 will be set and 3X reference will be used to control spark advance under 1200 RPM, and Bypass Mode will be in effect at under 400 RPM. The engine will continue to run and start normally.
If the 3X reference signal is not received by the PCM while the engine is running, the PCM will use the 24X reference pulses to calculate RPM and crankshaft position. The engine will continue to run and start normally, but DTC P1374 will be set.
Poor-engine performance and possibly a MIL with no DTC can be caused If the Reference Low circuit is open or connected to ground at the PCM.
The IC output circuitry in the PCM generates IC output pulses anytime crankshaft reference signal input pulses are being received. When the ignition system is operating in the Bypass Mode (no voltage on the bypass control circuit), the ignition control module grounds the IC pulses coming from the PCM. The ignition control module will remove the ground from the IC circuit only after switching to the IC Mode. The PCM commands switching to IC Mode by applying 5 volts on the bypass circuit to the ignition control module. The PCM monitors its own IC output, and expects to see no pulses on the IC circuit when it has not yet applied 5 volts on the bypass control circuit. When the second 3X reference pulse at the start of crank is seen by the PCM, it applies 5 volts to the bypass control circuit and the IC pulses should no longer be grounded by the ignition control module. The PCM constantly monitors its IC output, and should detect the IC pulses only when commanding the IC Mode. If the IC circuit is open, the PCM will detect IC output pulses while attempting to start the engine (in the Bypass Mode) due to the ignition control module not being able to ground the IC pulses. Three things will occur:
^ DTC P1350 will set.
^ The PCM will not apply 5 volts to the bypass circuit.
^ The engine will start and run in Bypass Mode.
If IC circuit is grounded, the PCM would not detect a problem until the change to IC Mode is commanded by the PCM. When the PCM applies 5 volts to the bypass control circuit, the ignition control module will switch to IC Mode. With the IC circuit grounded, there would be no IC pulses for the ignition control module to trigger the ignition coils, and the engine may falter. The PCM will quickly revert back to Bypass Mode (turn OFF the 5 volts on the bypass circuit), DTC P1361 will set, and the ignition system will operate in Bypass Mode until the fault is corrected and the engine is stopped and restarted.
If bypass circuit is open or grounded, the ignition control module cannot switch to IC Mode. In this case, the IC pulses will stay grounded in the ignition control module, and DTC P1361 will be set. The engine will start and run in Bypass Mode.
The following information will list important considerations to aid the technician in servicing the ignition system.
^ The ignition coils secondary voltage output capabilities are very high - more than 40,000 volts.
WARNING: Avoid body contact with ignition high voltage secondary components when the engine is running, or personal injury may result.
^ The 7X crankshaft sensor is the most critical part of the ignition system. If the sensor is damaged so that the sensor pulses are not generated or received by the Ignition Control Module, the engine will not start! There are 2 circuit wires connecting the 7X crankshaft position sensor to the ignition control module. If there is a problem with the wiring or crank sensor connections, the engine will not start (no spark and no injector pulses). If a fault occurs while the engine is running, the vehicle will stall and not restart.
^ The 24X crankshaft position sensor clearance is very important! The sensor must not contact the rotating interrupter rings at any time, or sensor damage will result. If the balancer interrupter rings are bent, the interrupter ring blades will destroy the sensor.
^ Ignition timing is not adjustable. There are no timing marks on the crankshaft balancer or timing chain cover.
^ If the 24X crankshaft position sensor is replaced, the crankshaft balancer must be removed first. The balancer is a press fit onto the crankshaft; removing the serpentine accessory drive belt and balancer attaching bolt will allow its removal with special tool J 38197.
^ When reinstalling, torque the balancer attachment bolt. This is critical to ensure the balancer stays attached to the crankshaft.
^ If a 24X crankshaft position sensor assembly is replaced, check the crankshaft balancer interrupter rings for any blades being bent. If this is not checked closely and a bent blade exists, the new crankshaft position sensor can be destroyed by the bent blade with only one crankshaft revolution!
^ Neither side of the ignition coil primary or secondary windings is connected to engine ground. Although the ignition coil packs are secured to the ignition control module, it is not an electrical connection to ground.
^ Be careful not to damage the secondary ignition wires or boots when servicing the ignition system. Rotate each boot to dislodge it from the plug or coil tower before pulling it from either a spark plug or the ignition coil. Never pierce a secondary ignition wire or boot for any purpose! Future problems are guaranteed if pinpoints or test lights are pushed through the insulation for testing.
^ The ignition control module is grounded to the engine block through a ground wire to the ignition control module bracket mounting stud. If servicing is required, ensure that good electrical contact is made between the ground and the mounting bracket, including proper hardware and torque.
^ A conventional tachometer used to check RPM on a primary ignition tach lead will not work on this ignition system. To check RPM, use either of the following items:
- A tachometer designed with an inductive pickup, used on the secondary side of an ignition system. These tachs are identified by a clamp that goes around a spark plug wire. Set the tach to 2-cycle operation. The 2-cycle setting is required because spark plugs on this engine fire every time the piston is at the top of its stroke. If a 2 cycle selection is not available, divide the indicated 4 cycle reading by 2.
- A scan tool.