Engine Cranks But Does Not Run

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Engine Controls Schematics: IGN Switch, PCM Feeds:

CIRCUIT DESCRIPTION
The electronic ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition control module triggers the correct coil based on the sync signal received from the crankshaft position sensor, resulting in both spark plugs connected to the coil firing at the same time. The spark plug for the cylinder on the exhaust stroke requires a lower energy requirement in order to fire, leaving the remaining high voltage to fire the spark plug for the cylinder on the compression stroke.

During crank, the ignition control module monitors the crankshaft position (CKP) sync signal. The CKP sync signal is used to determine the correct cylinder [1][2]pair to fire first. The CKP sync signal is used only by the ignition control module in order to initiate the ignition coil firing sequence. It is not passed to the PCM. After the ignition control module processes the CKP sync signal, the ignition control module monitors the 18X CKP signal and sends 18X and 3X reference pulses to the PCM. When the PCM receives these pulses, the PCM will command all six injectors in order to allow a priming shot of fuel for all the cylinders. After the priming, the injectors are left OFF during the next six 3X reference pulses from the ignition control module. This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, the PCM receives a camshaft position signal pulse. The camshaft position signal allows the PCM to operate the injectors sequentially, based on camshaft position. If the camshaft position signal is not present at start-up, the PCM will begin sequential fuel delivery with a 1 in 6 chance that fuel delivery is correct.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside the insulation. Check for the following items:
^ A shorted camshaft position sensor
An internally-shorted camshaft position sensor can cause an Engine Cranks but Will not Run condition. If the diagnostic table indicates a short to ground in the sensor ignition positive voltage circuit, disconnect the camshaft position sensor and attempt to start the vehicle. If the vehicle starts with the camshaft position sensor disconnected, a shorted camshaft position sensor is indicated.

^ A poor connection or a damaged harness
Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections, and a damaged harness.

^ A malfunctioning engine coolant temperature sensor
Using a scan tool, compare the engine coolant temperature with the intake air temperature on a completely cool engine. The engine coolant temperature should be within 10°C (50°F) of the intake air temperature. If it is not, replace the ECT sensor.

^ The throttle position (TP) sensor
If the TP angle is more than 80 percent, the PCM may operate in clear flood mode. The PCM will not allow fuel delivery while operating in clear flood mode.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
5. This step determines if the ignition control module (ICM) is receiving the 18X Crankshaft Position (CKP) Reference signal If the 18X CKP signal to the ICM is not present, there will be no RPM, no spark, and no fuel injector pulses.
6. This step ensures that the ICM has the proper voltage supply and ground.
8. This step verifies that the ignition control module (ICM) is supplying the proper sensor feed voltage.
24. Check for the proper operation of the CKP Sync signal, the ICM and the related spark system components. Without the CKP Sync signal the ICM is unable to properly sequence the ignition coils.
35. If the 18X and CKP Sync signals to the ICM or the 18X and 3X reference signals to the ICM short together, the vehicle will not start and run. However, there will be spark and fuel injector pulses.
46. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.