P0303

P0303-CYLINDER 3 MISFIRE

For a complete wiring diagram Consult Diagrams/Electrical.

- When Monitored:
Any time the engine is running, and the adaptive numerator has been successfully updated.

- Set Condition:
The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes 1 soft fail to set a malfunction and two trips to set the MIL. Three good trips to turn off the MIL.

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.

Diagnostic Test

1. ACTIVE DTC
Diagnose and repair any other active component or circuit DTCs before continuing with this procedure.
Turn the ignition on.
With the scan tool, select View DTCs. Copy DTC and Freeze Frame information.
Start the engine and allow it to reach operating temperature.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

NOTE: Attempt to operate the vehicle under conditions similar to which the DTC was set.

NOTE: It may be necessary to test drive the vehicle within the DTC monitoring conditions in order for this DTC to set.

With a scan tool, select View DTCs.
Is the DTC Active at this time?

Yes

- Go To 2

No

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

2. VISUAL INSPECTION
NOTE: Anything that affects the speed of the crankshaft can cause a misfire DTC.

NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.

- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys.
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector, Ignition coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
- Internal engine component failures.
Were any of the above conditions present?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 3

3. (F42), (A15) ASD RELAY OUTPUT CIRCUIT

Turn the ignition off.
Disconnect the No.3 Ignition Coil harness connector.
Disconnect the No.3 Fuel Injector harness connector.
Ignition on, engine not running.
With a scan tool, actuate the ASD Relay.
Using a 12-volt test light connected to ground, probe the (F42), (A15) ASD Relay Output circuit in the Ignition Coil harness connector and Fuel Injector harness connector while the relay is actuating.
Does the test light illuminate brightly?

Yes

- Go To 4

No

- Repair the excessive resistance or short to ground in the (F42), (A15) ASD Relay Output circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. IGNITION SYSTEM OPERATION
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Turn the ignition off.
Connect the Ignition Coil No.3 harness connector.
Remove the Ignition Coil.
Leave the Fuel Injector harness connector of the cylinder being tested disconnected.
Install a spark tester on the Ignition Coil.
While cranking the engine observe the spark coming from the spark tester.
Perform the same test on the ignition wire side of the Ignition coil.

NOTE: A crisp blue spark that is able to jump the gap of the spark tester should be generated at the coil on plug and at the end of the ignition wire.

Is good spark present?

Yes

- Go To 5

No

- Go To 14

NOTE: Connect the Fuel Injector harness connector before continuing.

5. SPARK PLUG
CAUTION: The 4.7L engine uses TWO DIFFERENT types of spark plugs. A total of 16 plugs are used. The plugs are mounted in two rows (banks). The upper row (5) is used on the intake valve side of the cylinder head. The lower row (6) is used on the exhaust valve side of the cylinder head. The upper row (5) uses Bosch Nickel Yttrium plugs #05149050AB. The lower row (6) uses Bosch Iridium plugs #05149888AA. DO NOT INTERCHANGE THESE PLUGS.

Turn the ignition off.
Remove the Spark Plug(s).
Inspect the Spark Plug(s) for the following conditions.
- Cracks
- Carbon Tracking
- Foreign Material
- Gap size out of specifications
- Loose or broken electrode

NOTE: Lightly tap the bottom of the spark plug on a solid surface. The electrode in the spark plug should not move.

Were any of the above conditions present?

Yes

- Replace the Spark Plug. Spark Plug - Removal
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 6

6. FUEL PRESSURE CHECK
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Install a fuel pressure gauge to the fuel rail.
Start the engine and observe the fuel pressure reading.

NOTE: Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

Choose a conclusion that best matches your fuel pressure reading.

Within Specification

- Go To 7

Below Specification

- Go To 12

Above Specification

- Replace the fuel filter/pressure regulator.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

7. FUEL PRESSURE LEAK DOWN
NOTE: Before continuing visually and physically inspect the fuel delivery system for external leaks or damage. Repair/replace as necessary.

WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death

Turn the ignition off.
Install special tool #6539 (5/16") or #6631 (3/8") fuel line adapter.
Install the fuel pressure gauge.
Start the engine and allow the fuel system to reach maximum pressure.
Turn the ignition off.

NOTE: Fuel specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

Using special tool #C4390, Hose Clamp Pliers, pinch the rubber fuel line between the fuel pressure gauge and the engine.
Monitor the fuel pressure gauge for a minimum of 5 minutes.

NOTE: The pressure should not fall below 241 kPa (35 psi).

Does the pressure fall below the listed specification?

Yes

- Replace the leaking Fuel Injector(s).
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 8

8. FUEL INJECTOR OPERATION
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.

CAUTION: After each Fuel Injector actuation, start the engine to clean the cylinder of fuel. Failure to do so could cause engine damage.

Remove special tool #C4390.
Start the engine and allow the fuel pressure to reach maximum pressure.
Ignition on, engine not running.
Using a scan tool, actuate the No.3 Fuel Injector.
Monitor the fuel pressure gauge.
Does the fuel pressure gauge indicate a drop in fuel pressure?

Yes

- Go To 9

No

- Go To 10

NOTE: Turn the ignition off, remove the Fuel Pressure gauge, and connect the fuel lines before continuing.

9. ENGINE MECHANICAL
Check for any of the following conditions/mechanical problems.
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
CAM LOBES - must not be worn excessively
CYLINDER LEAKAGE TEST - must be within specifications
VALVE SPRINGS - cannot be weak or broken
Are there any engine mechanical problems?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 17

10. FUEL INJECTOR
Turn the ignition off.
Disconnect the No.3 Fuel Injector harness connector.
Ignition on, engine not running.

NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.

With the scan tool, erase DTCs.
Install an Injector Noid light.
With the scan tool, actuate the Fuel Injector.
Does the Noid light blink/flicker during the actuation?

Yes

- Verify that there is good pin to terminal contact in the Fuel Injector and the Powertrain Control Module connectors. If OK, replace the Fuel Injector.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 11

11. (K13) INJECTOR CONTROL NO.3 CIRCUIT

Turn the ignition off.
Disconnect the C2 PCM harness connector.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.

Check the (K13) Injector Control No.3 circuit for an open, short to ground, and short to voltage.
Was a problem found with the (K13) Injector Control No.3 circuit?

Yes

- Repair the excessive resistance or short in the (K13) Injector Control No.3 circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 17

12. FUEL SUPPLY LINE RESTRICTED
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.

Turn the ignition off.
Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.
Install special tool #6539 (5/16") #6631(3/8") fuel line adapter and the fuel pressure gauge between the fuel supply line and the fuel pump module.
Ignition on, engine not running.
With a scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.

NOTE: Fuel pressure specification is 407 kPa +/- 34 kPa (59 psi +/- 5 psi).

Is the fuel pressure within specification?

Yes

- Repair or replace fuel supply line as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 13

13. FUEL PUMP INLET STRAINER
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.

Turn the ignition off.
Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer.
Is the Fuel Inlet Strainer plugged?

Yes

- Replace the Fuel Pump Inlet Strainer.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Before continuing, check the Fuel Pump Module harness connector terminals for corrosion, damage, or terminal push out. Make sure the ground circuit is functional. Repair as necessary. Replace the Fuel Pump Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

14. IGNITION WIRE
NOTE: If the vehicle being tested does not have an ignition wire answer YES to this test and continue.

Turn the ignition off.
Remove the ignition wire.
Measure the resistance of the ignition wire.
Is the resistance below 10K ohms?

Yes

- Go To 15

No

- Replace the Ignition Wire.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

15. IGNITION COIL

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.

Disconnect the No.3 Ignition Coil harness connector.
Remove the Fuel Pump Relay.
Using a 12-volt test light connected to 12-volts, probe the (K93) Coil Control No.3 circuit.
Crank the engine for 5 seconds while observing the test light.

NOTE: The primary resistance of the 3.7L and 4.7L Ignition coil is 0.6 to 0.9 of an ohm and the resistance of a 5.7L Ignition coil is 0.558 to 0.682 of an ohm at 25° C (77° F).

Does the test light brightly blink/flicker?

Yes

- Verify that there is good pin to terminal contact in the Ignition Coil and the Powertrain Control Module connectors. If OK, replace the Ignition Coil.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To 16

16. (K93) COIL CONTROL NO.3 CIRCUIT