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Home >> Chevrolet >> 1998 >> Forward Control P30, 6.5 F, Standard >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 4 (Engine Controls - Tests W/Codes - 7.4L) >> Diagnostic Trouble Codes >> DTC P0300-P0308 - Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different variant/trim than selected.
  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.
  2. Using scan tool, review FAILURE RECORDS DATA. Check if any other DTCs are set. If other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
  3. Using scan tool, perform CKP SYSTEM VARIATION LEARNING PROCEDURE. After performing CKP learn procedure, go to next step.
  4. Start and operate engine at idle. Using scan tool, monitor MAP sensor voltage. If MAP sensor voltage is greater than 4 volts, go to DTC P0108 diagnostic test. If MAP sensor voltage is not greater than 4 volts, go to next step.
  5. Using FREEZE FRAME and FAILURE RECORDS data on scan tool, duplicate conditions required for misfire. If scan tool indicates that this DTC failed this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed this ignition cycle, go to step 11).
  6. Using scan tool, review misfire index. If misfire index is increasing for more than one cylinder, see DIAGNOSTIC AIDS. If not, go to next step.
  7. Install Spark Tester (J 26792) on spark plug wire No. 1. Disconnect fuel injector harness at intake manifold. Crank engine. Spark should jump tester gap. Repeat for each spark plug wire. If spark is adequate on all spark plug wires, go to next step. If spark is not adequate on all spark plug wires, check ignition system. See BASIC TESTING - 7.4L article.
  8. Inspect spark plugs for wear, excessive air gap, cracks or fouling. If spark plug are okay, go to next step. If spark plugs are not okay, go to step 12).
  9. Perform a cylinder compression test. If a problem is found, go to step 14). If no problem is found, go to next step.
  10. Diagnose fuel injector circuit. See BASIC TESTING - 7.4L article. If a problem is found, go to next step. If no problem is found, go to step 13).
  11. Misfire is intermittent and not currently occurring. Check if additional DTCs are set. Diagnose affected DTCs. If no additional DTCs are set, see DIAGNOSTIC AIDS.
  12. Replace spark plugs. After replacing spark plugs, go to step 14).
  13. Repair circuit as necessary. After repairs, go to next step.
  14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
  15. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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