joatmon wrote: ↑
Sun Mar 29, 2020 12:16 pm
The 03 GM service manual lists the following things to check for poor gas mileage:
- Check the air cleaner element for dirt or restrictions
- Visually and physically check the vacuum hoses for splits, kinks, and proper connections
- Check the owner's driving habits for any of the following:
- The A/C system defroster mode is ON all the time
- The tires are improperly inflated
- Heavy loads are frequently being carried
- Heavy acceleration and high speeds are common
- Frequent short trips
- Prolonged periods of idling
- Driving on unpaved or rough roads
- Suggest that the owner refill the tank and recheck the fuel economy
Fuel System Checks
- Check the type, quality and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy
- Check for the correct fuel pressure
Ignition System Checks
- Inspect the spark plugs for correct operation and good igntion system performance.
- Check the ignition coil boots for cracking, chafing and loose connections.
- Observe the Spark parameter on the scan tool at idle, while operating the rear defogger, the A/C system or the headlights.
--If the scan tool display remains fixed at 10 degrees, check for a short to ground in the Diagnostic Request circuit from the powertrain control module (PCM) connector C4 terminal 20 to the data link connector (DLC)Check the knock sensor (KS) and the sensor circuit shielding.
--A faulty knock sensor or signal interference could cause excessive retard of the ignition timing advance.
- Observe the Spark parameter on a scan tool and compare with a known good vehicle. A typical value at 98 kmm/h(60 mph) with all engine accessories off is 26-32 degrees.
Cooling System Checks
- Check for the correct engine coolant level
- Check engine thermostat for always being open or for the wrong heat range.
- Check the clutch adjustment in vehicles equipped with a manual transmission.
- Check the transmission shift pattern and the torque converter clutch (TCC) operation in vehicles equipped with an automatic transmission.
- Check for dragging brakes
- Check for uneven or premature tire wear. A suspension misalignment can cause reduced fuel economy
- Verify that the wheels and tires are similar to OEM. Wide performance tires create more drag and taller tires can cause odometer discrepancies.
- Check for (sic) the speedometer for proper calibration
- Check for green engine. Fuel economy may not be near expected levels until the engine has had 5,000 - 8,000 km (3,000 - 5,000 miles) to break in.
- Check for add-on equipment like luggage racks and carriers. Wind resistance can lower fuel economy.
- Check the Service Bulletins for any updates or information.
at 200K on it, its not a "green engine" issue.
Other than poor gas mileage, have you noticed any performance issues, such as loss of power? There used to a genviber here pmh013 who had a lot of issues with her 03 AWD, horrible gas mileage and loss of power/acceleration, that ended up being from a clogged catalytic converter, which isn't listed in the excerpt above