Lack of Power, Sluggishness, or Sponginess. GMC Truck GMC C-Series Medium Duty Truck B7 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.0L and 7.0L 🢒 Lack of Power, Sluggishness, or Sponginess

Checks

Action

DEFINITION: The engine delivers less than the expected power. There is little or no increase in speed when partially applying the accelerator pedal.

Preliminary Checks

•	Refer to Symptoms for the Important Preliminary Checks.

•	Compare the customer's vehicle with a similar unit. Make sure the customer has an actual problem.

•	Remove the air filter. Check the filter for dirt or for being plugged.

•	Check the transmission shift pattern and down shift operation.

•	Check for fuel spray from both injectors. Refer to Engine Cranks but Does Not Run .

Fuel System Checks

•	Check for a restricted fuel filter, contaminated fuel, or improper fuel pressure. Refer to Fuel System Diagnosis .

•	Check for contaminated fuel.

Ignition System Checks

•	Check for the proper ignition voltage output with the spark tester J 26792 or equivalent.

•	Check the ignition timing and proper operation of the ignition control system. Refer to Distributor Ignition (DI) System Diagnosis .

Exhaust System Checks

•	Check the exhaust system for a possible restriction: Refer to Engine Exhaust.

•	Inspect the exhaust system for damaged or collapsed pipes.

•	Inspect the muffler for heat distress or a possible internal failure.

Additional Checks

•	Check the ECM grounds for being clean, tight, and in their proper location.

•	Check the EGR Valve for being open or partly open all of the time. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .

•	Check the generator output voltage.

Engine Mechanical Check

-	Compression

-	Valve timing

-	Proper or worn camshaft