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Home >> Chrysler >> 2002 >> PT Cruiser Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Multiple Cylinder Misfire, DTC P0301: Cylinder #1 Misfire, DTC P0302: Cylinder #2 Misfire, DTC P0303: Cylinder #3 Misfire Or DTC P0304: Cylinder #4 Misfire >> Testing

DTC P0300: Multiple Cylinder Misfire, DTC P0301: Cylinder #1 Misfire, DTC P0302: Cylinder #2 Misfire, DTC P0303: Cylinder #3 Misfire Or DTC P0304: Cylinder #4 Misfire: Testing

NOTE: If any other DTCs are present in PCM, repair those DTCs first.
  1. With the DRBIII®, read DTCs. Is the Misfire Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  8.
  2. At this time, conditions required to set the Misfire DTC are present. With the DRBIII®, select DTCs and Related Functions. Read and record the Freeze Frame Data. Select OBD II Monitors. Read and record the Misfire Similar Conditions Window Data. With these screens, attempt to duplicate the condition(s) that has set this DTC. When the vehicle is operating in the Similar Conditions Window, refer to the Which Cylinder Is Misfiring screen for at least one minute. Is the DRBIII® counting misfires at this time? If yes, go to next step. If no, go to step  8.
  3. Start the engine and allow the engine to idle. With the DRBIII®, read the Freeze Frame Data and attempt to determine the cause of the Misfire DTC. In the Freeze Frame, are the adaptive fuel percentages greater than plus or minus 15 percent? If yes, check fuel delivery system. See FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If no, go to next step.
  4. With the DRBIII®, read the Freeze Frame Data. Use the Freeze Frame Data and attempt to determine the cause of the Misfire DTC. In the Freeze Frame Data, is the Load Value over 50 percent and the operating temp normal? If yes, check secondary ignition, compression and cylinder leakage. If no, go to next step.
  5. With the DRBIII®, read the Freeze Frame Data. Use the Freeze Frame Data and attempt to determine the cause of the Misfire DTC. In the Freeze Frame Data, is the engine RPM over 3000 and the operating temp normal? If yes, test CMP and CKP signals with lab scope, check valve timing, and perform running vacuum test. If no, go to next step.
  6. Check for any of the following conditions/mechanical problems:
    • Ensure engine vacuum is at least 13 in. Hg with transmission in Neutral.
    • Ensure valve timing is within specification.
    • Ensure compression is within specification.
    • Ensure exhaust is free from restrictions or leaks.
    • Ensure PCV system flows freely.
    • Ensure torque converter stall speed is within specification.
    • Ensure power brake booster has no internal vacuum leaks.
    • Ensure fuel is not contaminated.
    • Ensure fuel injector is not plugged or restricted.
    • Ensure fuel injector harness connectors are connected to correct fuel injectors.

    Are there any engine mechanical problems? If yes, repair as necessary. If no, go to next step.

    7. NOTE: Anything that affects the speed of the crankshaft can cause a misfire.
  7. The following are other possible causes for misfire: injector harness connectors, secondary ignition problem, mechanical engine problem, PCM power grounds, irregular cam and crank signal, plugged injectors, restricted exhaust, intake restriction, damaged trigger wheel, contaminated fuel, or vacuum leak. Weak valve springs, carbon deposits on valves, or accessory drive belt (serpentine belt). Check for any TSBs that may relate to a Misfire DTC. Do any of the above causes exist? If yes, repair as necessary. If no, test is complete.
  8. At this time the misfire does not exist or is an intermittent problems. An intermittent problem may have been caused by moisture in the secondary ignition. With the DRBIII®, select DTCs and Related Functions. Read and record the Freeze Frame Data. Select OBD II Monitors. Read and record the Misfire Similar Conditions Window Data. With these screens, attempt to duplicate the condition(s) that has set this DTC. While using Freeze Frame Data, pay particular attention to the DTC setting conditions, such as speed, temp, load and MAP vacuum. Does the misfire reoccur? If yes, go to next step. If no, Misfire DTC conditions no longer exist. Refer to any TSBs that may relate to the symptom. Operate the vehicle for 2 misfire good trip and erase DTCs.
  9. Start the engine and allow the engine to idle. With the DRBIII®, read the Freeze Frame Data. Use the Freeze Frame Data and attempt to determine the cause of the Misfire DTC. In the Freeze Frame, are the adaptive fuel percentages greater than plus or minus 15 percent? If yes, check fuel delivery system. See FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If no, go to next step.
  10. With the DRBIII®, read the Freeze Frame Data. Use the Freeze Frame Data and attempt to determine the cause of the Misfire DTC. In the Freeze Frame Data, is the Load Value over 50 percent and the operating temp normal? If yes, check secondary ignition, compression and cylinder leakage. If no, go to next step.
  11. With the DRBIII®, read the Freeze Frame Data. Use the Freeze Frame Data and attempt to determine the cause of the Misfire DTC. In the Freeze Frame Data, is the engine RPM over 3000 and the operating temp normal? If yes, test CMP and CKP signals with lab scope, check valve timing, and perform running vacuum test. If no, go to next step.
  12. Check for any of the following conditions/mechanical problems:
    • Ensure engine vacuum is at least 13 in. Hg with transmission in Neutral.
    • Ensure valve timing is within specification.
    • Ensure compression is within specification.
    • Ensure exhaust is free from restrictions or leaks.
    • Ensure PCV system flows freely.
    • Ensure torque converter stall speed is within specification.
    • Ensure power brake booster has no internal vacuum leaks.
    • Ensure fuel is not contaminated.
    • Ensure fuel injector is not plugged or restricted.
    • Ensure fuel injector harness connectors are connected to correct fuel injectors.

    Are there any engine mechanical problems? If yes, repair as necessary. If no, test is complete.

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