Ignition System Overview
The electronic ignition system controls fuel combustion by providing
a spark to ignite the compressed air/fuel mixture at the correct time. To
provide optimum engine performance, fuel economy, and control of exhaust
emissions, the PCM controls the ignition system. The Electronic ignition
system has the following advantages over a mechanical distributor system:
| • | Remote mounting capability. |
| • | No mechanical load on the engine. |
| • | More coil cool down time between firing events. |
| • | Elimination of mechanical timing adjustments. |
| • | Increased available ignition coil saturation time. |
The electronic ignition system does not use the conventional
distributor and coil. The ignition system consists of the following components/circuits:
| • | Six Ignition Control (IC) circuits |
| • | Two Ignition Control Modules (one per cylinder bank) |
| • | Camshaft Position (CMP) sensor |
| • | Crankshaft Position (CKP) sensor |
| • | Related connecting wires |
| • | Powertrain Control Module (PCM) |
Crankshaft Position Sensor
The Crankshaft Position (CKP) sensor (2) used
on this engine is actually two sensors within a single housing. Each sensor
has a separate power, ground and signal circuit. The PCM supplies 12
Volts to both sensors. The PCM provides the ground path, or sensor return
circuit, from both sensors. These power and ground circuits are also
connected to the CMP sensor. Two separate signal circuits connect the
CKP sensor and the PCM.
The PCM can use three different modes of decoding crankshaft position.
During normal operation, the PCM performs an Angle Based calculation using
both signals to determine crankshaft position. The dual sensor allows
the engine to run even if one signal is lost. If either signal is lost,
the PCM switches to a Time Based method of calculating crankshaft position.
If the system is operating in Time A mode, the PCM is using only the
signal from Sensor A. Time B indicates that the Sensor B signal is being
used. If the lost signal is restored, the PCM will continue to operate
in Time based mode for the remainder of the current key cycle. The PCM
will revert back to the Angle mode on the next start if the fault is
no longer present. The scan tool can display the Crank Position Sensing
Decode Mode. A problem with sensor A will set DTC P0335. A problem with
sensor B will set P0385.
Camshaft Position Sensor
The Camshaft
Position (CMP) sensor signal, when combined with the CKP sensor signal, enables
the PCM to determine exactly which cylinder is on a firing stroke.
The PCM can then properly synchronize the ignition system, fuel injectors
and knock control. The CMP sensor has a power, ground and signal circuit.
The PCM supplies 12 Volts to the sensor. The PCM provides the ground
path, or sensor return circuit, from the sensor. These power and ground
circuits are also connected to the CKP sensor. If a problem is detected
with the CMP circuit, DTC P0340 will set.
Ignition Coils/Modules
The ignition system on this engine uses an individual
ignition coil for each cylinder. An ignition coil assembly consisting of
three coils and an ignition control module, is located in the center
of each cam cover. This arrangement allows the ignition coil to
connect directly to the spark plug using only a boot. This eliminates
the need for secondary ignition wires. There are separate ignition
modules for Bank 1 and for Bank 2. Each module controls the three
ignition coils for that bank of cylinders. The PCM controls ignition
module operation. There are six Ignition Control (IC) circuits, one
per cylinder, that connect the PCM and the ignition modules. The
ignition modules also have a power feed, a chassis ground circuit
and a Reference Low circuit each. The PCM causes spark to occur
by pulsing the IC circuit, which signals the ignition module to trigger
the ignition coil and fire the spark plug. Sequencing and timing
are PCM controlled.
The ignition feed circuits are fused separately for each bank of the
engine. The two fuses also supply the injectors for that bank of the engine.
This system puts out very high ignition energy for plug firing. Because
there are no ignition wires, there is no energy loss due to ignition wire
resistance. Also, since the firing is sequential, each coil has five
events to saturate as opposed to the two in a waste spark arrangement.
Futhermore, no energy is lost to the resistance of a waste spark system.
Noteworthy Ignition Information
There are important considerations to point out when servicing the ignition
system. The following Noteworthy Information will list some of these, to help
the technician in servicing the ignition system.
| • | The ignition coils secondary voltage output capabilities are very
high - more than 40,000 volts. Avoid body contact with ignition
high voltage secondary components when the engine is running, or personal
injury may result! |
| • | The crankshaft position sensor is the most critical part of the
ignition system. If the sensor is damaged so that pulses are not generated,
the engine will not start! |
| • | Crankshaft position sensor clearance is very important! Excessive
clearance can result from improper installation, dirt/debris or the old O-ring
left in the block cavity when a new sensor is installed. Insufficient clearance
will damage the sensor. The sensor must not contact the rotating crankshaft
reluctor wheel at any time. Sensor to reluctor wheel clearance is not adjustable. |
| • | Ignition timing is not adjustable. There are no timing marks on
the crankshaft pulley. |
| • | If a boot remains attached to a coil or spark plug, twist the
boot prior to removal. |
| • | Check the boot for a missing or damaged internal spring. |
| • | Do not re-install any component that has visible signs of damage. |
| • | Install the boots onto the coils (until bottomed out). Then install
the assembly onto the spark plugs. If this is not possible due to space limitations,
just-start the boots onto the spark plugs and then install the coil
assembly as straight down onto the plugs as possible. |
| • | Ensure the boots are installed right side up. |
| • | Lift the module beauty cover at the end opposite the module to
remove. |
| • | Repair a torn perimeter seal with RTV sealant. |
Powertrain Control Module (PCM)
The PCM is responsible for maintaining proper spark and fuel injection
timing for all driving conditions. To provide optimum driveability and emissions,
the PCM monitors input signals from the following components in calculating
Ignition Control (IC) spark timing:
| • | Engine Coolant Temperature (ECT) sensor. |
| • | Intake Air Temperature (IAT) sensor. |
| • | Mass Air Flow (MAF) sensor. |
| • | Trans Range inputs from Transaxle Range switch. |
| • | Throttle Position (TP) sensor. |
| • | Vehicle Speed Sensor (VSS). |
Results of Incorrect Operation
An Ignition control circuit that is open, grounded, or short to voltage
will set an ignition control circuit DTC. If a fault occurs in the IC output
circuit when the engine is running, the engine will experience a misfire.
DTCs P1351-P1366 indicate that a malfunction has been detected
on an Ignition Control circuit.
The PCM uses information from the engine coolant temperature sensor
in addition to RPM to calculate spark advance values as follows:
| • | High RPM = more advance |
| • | Cold engine = more advance |
| • | Hot engine = less advance |
Therefore, detonation could be caused by high resistance in the engine
coolant temperature sensor circuit. Poor performance could be caused by low
resistance in the engine coolant temperature sensor circuit.
If the engine cranks but will not run or immediately stalls,
the Engine Cranks But Will Not Run diagnostic table must be used to determine
if the failure is in the ignition system or the fuel system.
