GM 6.5L V8 – Fuel System – Rough Idle Diagnosis Check

1. Check fuel injection pump static timing:
• Align the front cover and injection pump marks.

2. Check low idle speed (refer to page 7-87 for the complete procedure steps):
• Adjust to the vehicle emission label specification.

3. Inspect fuel injection lines and nozzles for fuel leakage:
• Repair any leakage.

4. Check fuel supply to the injection pump (refer to page 7-68 for the complete procedure steps):
• Minimum volume is 0.24 liter (1/2 pint) in 15 seconds.
• Minimum pressure is 40 kPa (5.8 psi).
• Fuel must be free of air bubbles.
• Make repairs, if needed.

5. Check the fuel return from the injection pump (refer to page 7-76 for the complete procedure steps):
• Fuel must be free of air bubbles.
• Repair injection pump, if needed.

6. Check each nozzle during engine operation:
• Loosen the injection line fitting nut at the nozzle to be tested.
• Observe that solid fuel flows from the line (no air bubbles).
• If air bubbles exist, go to step 7.
• If air bubbles do not exist, go to step 8.

7. Check a nozzle during engine cranking:
• Remove the B+ wire from the injection pump fuel shut-off solenoid.
• Remove and relocate the injection line to observe the nozzle inlet.
• Crank the engine and watch for air bubbles at the nozzle inlet fitting.
• If bubbles exist, replace the nozzle and go to step 8.
• Install all injection lines and remove all glow plugs.
• Crank the engine while observing the fuel mist exiting each glow plug hole.
• If no mist is present at any of the glow plug holes, remove and test the related injection nozzle.

8. Follow the steps of the glow plug resistance check (see next page).

 

Leave a Reply

Your email address will not be published. Required fields are marked *