03 SSEI Terrible Gas Mileage????? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-07-2010, 02:07 AM   #1
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Default 03 SSEI Terrible Gas Mileage?????

Any Ideas, I had a tech II scan ran and everything was clear, no codes in any modules. I have driven about 100 miles and used a half tank. Just normal driving, nothing excessive. Just got the car this week. Is the mileage just this shitty or is something wrong? God I hope this isn't what I have to deal with. I am getting about 14 a gallon.....
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Old 05-07-2010, 02:53 AM   #2
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Is that city or highway driving? When'* the last time the car had a tune up? Checked the air filter?
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Old 05-07-2010, 02:58 AM   #3
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Air filter is great, Looks Brand new. The guy I bought it from said it was tuned up recently. It does have all clean and fresh fluids..... I guess I could change the plugs, wires and fuel filter. Any other Ideas?
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Old 05-07-2010, 03:02 AM   #4
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Take a look at the plugs, you can generally tell if something is amiss by what they look like. Let us know what you find. The gear heads should be able to better help you whenever they wake up.
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Old 05-07-2010, 09:11 AM   #5
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You said you had a tech 2. Nice. When you ran the scan did you notice if the O2 mV'* were toggling fast from 100'* to 800'*? That is how you tell if the O2 sensor is good. Your O2 controls most of the fueling/richness issues when the rest of the car appears to run properly. After that the next biggest item would be a dirty MAF sensor.
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Old 05-07-2010, 09:21 AM   #6
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Old O2 sensor, dirty MAF, worn out plugs, old plug wires, weak coils, heavy foot. All of these can cause low mileage. Start with a good tune up. Never trust the last owner. Always new fluids and full tune up.
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Old 05-07-2010, 12:17 PM   #7
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If an o2 was bad would there be a code? I am used to working on Audis and VW'* and they will have a code and basically tell you exactly what'* up. My coworkers brother is a tech at a gm dealer and he brought the tech II to our shop yesterday. Everything was good except for something to do with onstar.
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Old 05-07-2010, 12:32 PM   #8
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A code only comes up with a total failure, not if it'* getting slow.
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Old 05-07-2010, 02:32 PM   #9
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Actually there is an insufficient switching code. Probably doesn't become an issue until the car sees about 5 gallons per mile though.
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Old 05-16-2010, 05:13 AM   #10
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Hi there,

I would start looking where Bill and Dan suggested. However, I had a coolant temp sensor fail which resulted in horrible milage. Check the coolant temp with the Tech II and see what it reads....if it shows a very low temp, the pcm will think that it is cold and adjust to a very rich mixture. If your sensor is totally bad like mine was, your car would run terribly. My PCM thought it was -40 F and really dumped the fuel to her. Perhaps the sensor can degrade partially? Just a thought....good luck
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