Really poor gas mileage. Looking for help.

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awdVibeNoobie
Posts: 38
Joined: Sat Jul 20, 2019 6:56 am
Location: Michigan

Really poor gas mileage. Looking for help.

Post by awdVibeNoobie » Sun Mar 29, 2020 11:29 am

My Vibe became my daily driver and have recently noticed that it's getting really poor gas mileage. I just looked at the spark plugs and they don't look that bad. I will change that out anyways along with new coil packs. Where else should I be looking to finding out what is causing my poor mpg? BTW the Vibe has little over 204,000 miles now. What is everyone getting for mpg with over 200,000 miles on your Vibe/Matrix?
03 awd Vibe my backup vehicle

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joatmon
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Location: SMC MD

Re: Really poor gas mileage. Looking for help.

Post by joatmon » Sun Mar 29, 2020 12:16 pm

The 03 GM service manual lists the following things to check for poor gas mileage:

Preliminary Checks
- 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.

Additional Checks
- 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

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tpollauf
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Re: Really poor gas mileage. Looking for help.

Post by tpollauf » Sun Mar 29, 2020 3:25 pm

Can't really offer too much help as all my Vibes are under your requested mileage. My 2004 Vibe GT gets a healthy 32mpg (90% hwy) and is just under 150K miles. Give us a better explanation of how/when the mileage dropped off. Do you log each tank to track mileage? I do, and have always for all my vehicles. It becomes a valuable tool (log book) when something goes wrong. Give us more information and maybe we'll pinpoint the problem.
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2009 Vibe GT (manual), 2009 G8Gt, 2009 Vibe GT (auto)
2014 Silverado, 2004 Vibe GT, 2003 Vibe GT (project car)

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awdVibeNoobie
Posts: 38
Joined: Sat Jul 20, 2019 6:56 am
Location: Michigan

Re: Really poor gas mileage. Looking for help.

Post by awdVibeNoobie » Sun Mar 29, 2020 4:17 pm

joatmon wrote:
Sun Mar 29, 2020 12:16 pm
The 03 GM service manual lists the following things to check for poor gas mileage:

Preliminary Checks
- 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.

Additional Checks
- 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
Thanks for the info you provided. That was one thing I was wondering if it's fuel related as the fuel filter needs to be replaced, dirty/clogged fuel injectors or carboned up throttle body (not sure if this is a problem with this old of a vehicle?).

How do you check/test to see if the cat is clogged? I'm not sure if I lost power on acceleration as this the slowest vehicle I've ever owed and was one of my first complaints how slow it is when I first got this.
tpollauf wrote:
Sun Mar 29, 2020 3:25 pm
Can't really offer too much help as all my Vibes are under your requested mileage. My 2004 Vibe GT gets a healthy 32mpg (90% hwy) and is just under 150K miles. Give us a better explanation of how/when the mileage dropped off. Do you log each tank to track mileage? I do, and have always for all my vehicles. It becomes a valuable tool (log book) when something goes wrong. Give us more information and maybe we'll pinpoint the problem.
Sorry I didn't specify that it's highway driving where I'm experiencing poor gas mileage. I've never got into logging in miles during fill up to calculate my mileage. I'm traveling about 100 miles a day for work and found that I have to fill up almost every other day. The job that I had fall of last year I was traveling about 40 miles a day for work and I was filling up about every 7 days. Btw math is never my strong suit.
03 awd Vibe my backup vehicle

jolt
Posts: 751
Joined: Sun Mar 02, 2014 2:07 am
Location: Twin Cities, Minnesota

Re: Really poor gas mileage. Looking for help.

Post by jolt » Mon Mar 30, 2020 1:07 am

Plugged cat, doing a search:

https://shop.advanceautoparts.com/r/adv ... verter-bad

https://www.2carpros.com/articles/how-t ... -converter

Check for codes (P0420 is common for a cat), past history of problems, temp check, and the age old way of checking for plugged exhaust is a vacuum gauge. Both above links talk of these things and if you would search, you would find more sites with the same info. There may be two cats, a pre-cat at the exhaust manifold and then a down stream cat too.

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