Poor Fuel Economy. GMC Truck GMC P42 Commercial Chassis 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 6.5L (L57) 🢒 Poor Fuel Economy

Poor Fuel Economy EFI

Checks

Action

Definition: The fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Preliminary Checks

•	Refer to Symptoms .

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

•	Visually (physically) check: The vacuum hoses for splits, kinks, and proper connections.

•	Check the driving habits of the owner.

•	Is the A/C ON full time (is the defroster mode ON)?

•	Are the tires at the correct pressure?

•	Are any excessively heavy loads being carried?

•	Is the acceleration too much, too often?

•	Suggest to the owner to fill the fuel tank and recheck the fuel economy.

•	Suggest to the driver to read the Important Facts on Fuel Economy in the Owner Manual.

Fuel System Checks

•	Check the fuel type and quality. Refer to Fuel Quality Diagnosis .

•	Check the fuel pressure. Refer to Fuel Supply System Check .

Cooling System Checks

•	Check the engine coolant level.

•	Check the engine thermostat for always being open or for the wrong heat range.

Additional Checks

•	Check the transmission shift pattern.

•	Check the Torque Converter Clutch (TCC) operation. When the TCC is commanded ON, a Scan Tool should indicate an RPM drop.

•	Check the Service Bulletins for any control module software updates.

•	Check for dragging brakes. Refer to the appropriate service manual.

Poor Fuel Economy MFI