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Home >> GMC >> 1997 >> Forward Control 4.3 W, L35, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 59 (Engine Controls - Tests W/Codes - 5.0L - G Vans) >> Diagnostic Trouble Codes >> DTC P0300 - Misfire Detected >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 1997 GMC Savana, 1997 Chevrolet Chevy Van, and 1997 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the F - BASIC TESTING - 5.0L article. After performing OBD system check, go to next step.
  2. Check if any other DTCs are set. If any other DTCs are set, go to applicable DTC test. If no other DTCs are set, go to next step.
  3. Install scan tool. With engine idling, monitor MAP sensor voltage using scan tool. If MAP sensor voltage is greater than 4 volts, go to DTC P0108  . If MAP sensor voltage is not greater than 4 volts, go to next step.
  4. Duplicate conditions required for misfire. Check if DTC is set as current for this ignition cycle. If DTC is set as current, go to next step. If DTC is not set as current, go to step 10).
  5. 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.
  6. 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, go to step 11).
  7. 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).
  8. Perform a cylinder compression test. If a problem was found, go to step 14). If a problem was not found, go to next step.
  9. Diagnose fuel injector circuit. See the F - BASIC TESTING - 5.0L article. If a problem was found, go to next step. If a problem was not found, go to step 13).
  10. Misfire is intermittent and not currently occurring. See DIAGNOSTIC AIDS.
  11. Perform enhanced ignition system check. See the F - BASIC TESTING - 5.0L article.
  12. Replace spark plugs. After replacing spark plugs, go to step 14).
  13. Repair circuit as necessary. After repairs, go to step 14).
  14. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0300. 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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