P0303 Cylinder 3 Misfire

P0303 Cylinder 3 Misfire, with the engine running, the adaptive numerator has been succesfully updated. Set conditions, the variation in crankshaft speed between each cylinder exceeds a calibrated value, based on engine rpm load. Default actions, the MIL light illuminate.

P0303 Cylinder 3 Misfire

Possible Causes P0303 Code:
  • ASD relay output.
  • Injector control circuit.
  • Coil control circuit.
  • Ignition wire.
  • Spark plug.
  • ignition coil.
  • Fuel delivery system issue.
  • Fuel injector.
  • Engine mechanical.
  • Powertrain Control Module (PCM).

Diagnose code P0303 Cylinder 3 Misfire

(Sorry!!! Step 1-2, refer to code P0301)
Step 1. Check for an active DTC
Step 2. Visual Inspection

(Step 3-5, refer to code P0302)
Step 3. Ignition system operation
Step 4. Spark plug
Step 5. Fuel pressure check

Step 6. Fuel pressure leak down
Perform the fuel pressure leak down test.

Were any repairs made after performing the leak down test?

Yes, testing complete.

No, go to step 7.

Step 7. Fuel injector operation
After each fuel injector actuation, start the engine to clean the cylinder of fuel. Failure to do so could cause engine damage.
Open the fuel system isolation valve. Start the engine and allow the fuel pressure to reach maximum pressure. Turn the ignition off. Turn the ignition on, with the scan tool, actuate the fuel injector for the cylinder that indicated the misfire. Monitor the fuel pressure gauge.

Does the fuel pressure gauge indicate a drop in fuel pressure?

Yes, go to step 8.
No, go to step 9.

Note: Turn the ignition off, remove the fuel pressure decay tester and connect the fuel lines before continuing.

Step 8. 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 specifications.
  • Engine compression - must be specifications.
  • Cylinder leakage test - must be specifications.
  • Engine exhaust system - must be free of any resrtictions 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.
  • Valve springs - cannot be weak or broken.
  • Cam lobes - must not be worn excessively.
  • Cam shafts - must not worn or have excessive endplay.
Are there any engine mechanical problems?

Yes, repair as necessary.

No, go to step 17.

(Sorry!!! Step 9-11, refer to code P0304)
Step 9. Fuel injector control
Step 10. Injector control circuit
Step 11. Fuel supply line restricted

(Sorry!!! Step 12-14, refer to code P0305)
Step 12. Fuel pump inlet strainer
Step 13. ASD relay output circuit
Step 14. Ignition coil

(Sorry!!! Step 15-17, refer to code P0306)
Step 15. Coil control 3 circuit shorted to ground
Step 16. Coil control 3 circuit open
Step 17. Powertrain Control Module (PCM)

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