GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1996 🢒 Corvette 🢒 Engine 🢒 Engine Controls - 4.3L (Caprice Only) and 5.7L 🢒 Distributor Ignition (DI) System

The distributor ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide improved engine performance, fuel economy, and control of exhaust emissions, the PCM controls distributor spark advance (timing) with an Ignition Control (IC) system. Only the IC system will be described here. Additional information on the system is found in Ignition System (6D).

To properly control ignition/combustion timing the PCM needs to know:

    • Camshaft position.
    • Engine speed (RPM).
    • Engine load (manifold pressure or vacuum).
    • Atmospheric (barometric) pressure.
    • Engine coolant temperature.
    • The amount of detonation.

Distributor Ignition System
Object Number: 13646 Size: SH
(1)Ignition Coil Wire
(2)Distributor
(3)Ignition Coil
(4)Ignition Coil Module

The distributor ignition system is a net build distributor (no timing adjustment) that provides angle based timing information to the PCM for individual cylinder spark timing. The ignition module is capable of providing both 4X and 180X timing pulses each crankshaft revolution. Using these timing pulses, the PCM processes ignition spark timing and sends an IC signal to the ignition coil module to activate the secondary ignition system.

The PCM provides the distributor with the following:

    • Ignition voltage circuit.
    • Ground circuit.
    • Two 5 volt reference voltages to the ignition control module.

As the camshaft turns (during crank or run), a slotted two-track timing disk is rotated inside the ignition control module. Each time a slot in either track of the disk is properly aligned, the ignition control module will pulse one of the 5 volt reference voltages to ground. A reference signal is generated each time the PCM detects that the reference voltages have been grounded by the ignition control module. When the PCM detects reference signals, ignition timing can be processed.

The PCM will also compare the 4X and the 180X signals to each other to determine the location of the number one cylinder and top dead center. In addition, if only one signal is being received by the PCM a Diagnostic Trouble Code (DTC) will be set. DTC P1371 will be set if the 4X signal is missing and DTC P0372 will be set if the 180X signal is missing. The vehicle will not run if the 4X (Reference) signal is not available at the PCM for processing.

The Ignition Control (IC) system consists of the following:

    • Camshaft Position Sensor
    • Ignition Coil
    • Ignition Coil Module
    • Powertrain Control Module.

These circuits perform the following functions:

    • Low resolution signal reference.
       - This provides the PCM with reference signals, firing order, and camshaft position information. If the low resolution signal circuit becomes open or grounded, the engine will not run because the PCM will not operate the ignition coil module, fuel pump, or the fuel injectors.
       - A DTC P1371 will set if the PCM receives high resolution signal references without the low resolution signals. If the engine cranks but will not start, refer to Engine Cranks but Does Not Run .
    • High resolution signal reference.
       - This provides the PCM with detailed reference signals and crankshaft position information.
       - If this circuit becomes opens or grounded a DTC P0372 will set and the engine will still run.
       - When there is a malfunction with the high resolution circuit, excessive crank times will be experienced.
    • System ground.
       - This circuit is grounded at the PCM and provides ground for the distributor to generate low and high resolution signal reference signals.
       - If this circuit becomes open, the engine will not run since there will be no reference information.
    • Ignition Control (IC).
       - This circuit controls the ignition coil ON and OFF time. It signals the ignition coil module to begin primary coil dwell current when the IC is high. The ignition coil module shuts OFF ignition coil current when the signal goes low.
       - If this circuit becomes open, shorted to voltage, or grounded, the engine will not start and a DTC P1351 or P1361 will set.

Ignition Wire Harness Assembly Routing
Object Number: 13492 Size: LF
(1)Cylinder #1
(2)Cylinder #2
(3)Cylinder #3
(4)Cylinder #4
(5)Cylinder #5
(6)Cylinder #6
(7)Cylinder #7
(8)Cylinder #8
(9)Distributor Assembly

Results of Incorrect Operation

An open IC circuit will set a DTC P1351. A grounded IC circuit will set a DTC P1361. An open or grounded IC circuit will result in an engine cranks but will not run. An open or ground in the low resolution signal circuit will set a DTC P1371 and the engine will not start. If the high resolution signal circuit becomes open or grounded a DTC P0372 would set. This will cause reduced performance and poor fuel economy.

An inoperative distributor vent system may cause premature distributor failure. To check system operation perform Distributor Vent System Check .

The PCM uses information from the MAP and engine coolant temperature sensor in addition to RPM to calculate spark advance as follows:

    • Cold engine = More spark advance.
    • Engine under minimum load based on RPM and low amount of air flow - More spark advance.
    • Hot engine = Less spark advance.
    • Engine under heavy load based on RPM and high amount of air flow - Less spark advance.

For removal and replacement of ignition system components, refer to Section 6D4, Ignition System.

The description, operation and repair procedures of the distributor ignition system components are found in Service Category Ignition Systems. For misfire or ignition control check, refer to the following DTCs:

    • P0300
    • P0323
    • P0372
    • P1351
    • P1361
    • P1371