Posted: Sun Jul 29, 2012 6:03 pm Post subject: changed O2 sensor
well i changed my O2 sensor yesterday morning. didnt take long at all about 15 min actually, thought it was going to be hell. anyways as some may know i made a thread about my impala losing 130 miles of range. i replaced my cat with a aftermarket from muffler shop. it was bad and also had a tear at the flange. got the car scanned for any codes and it showed tps and mps , i replaced the tps and still bad gas. although she runs slightly better , now sometime before i got it scanned and a O2 sensor code came up. i didnt pay it no mind since the check engine light went away. well after i did all this replacing of well not a lot but 3 things. cat ,flange pipe, tps and now O2 sensor. although i notice that it takes 50 miles or so for the gas needle to move from F. since the bad gas problem started it took 30 miles, so i noticed a 20 mile improvement after the O2 sensor change. so right now im at 170 miles and i have a bit over a 4th of a tank left. so what could be causing the mileage drop ? i cleaned my intake , MAF and seafoamed before the new O2 change , temp sensor . im going to put some injector cleaner in it to see if that helps . just want to get my 330 miles to a tank back lol its driving me nuts. i reset the comp after the O2 change but also cleaned the MAF this morning and did it then as well . do i need to give the comp time to adjust after a 1st fill after O2 sensor change ?
What kind of driving do you do? When I still had the Monte Caro, I was about 90% city driving and was sitting at about a quarter of a tank after 160 miles and it would usually take about 11 gallons of gas. Also, I'd pretty much forget about using the fuel gauge to determine your fuel consumption (it's a terribly inaccurate method) and calculate by hand. Once you have a value that way, we will be able to tell you if you are doing OK or not.
Protip: If you don't know what you're doing, don't do it.
mostly highway , i pretty much have a pattern lol. i do hand calculations i just know my needle moves off F at 70 miles. hand calculated i was getting 11mpg i dont know yet with the new O2 sensor . just out of the blue on july 2 i started getting bad gas mileage.
ive lost count its just bad i havent really been anywhere since it happened. its like im driving a 70s silverado. what could cause this and ive changed the important things. i noticed a slight increase after the O2 sensor would a new gas cap help some. car still has original plug and wires.
thats what i thought at 1st as well. i filled it up with QT gas and thats when it started. gas station was brand new as well lol. i filled up with other gas stations and still the same problem . cleaned air filter , maf sensor and new tps . even got a new temp sensor since i put a new thermostat in it . was getting 23 mpg now im getting 11
Posted: Sun Jul 29, 2012 8:26 pm Post subject: fuel mileage
When you are monitoring the movement of the gauge off of the full mark, It depends on how much gas you put in when you fill the tank. Do you always fill to the max you can get in the tank? That will be more than 17 gallons. If I fill to absolute max I can get almost 19 gallons in. To a point where the gas is not quite spilling out the fill neck. Doing it this way it takes forever for the needle to start to move from the full mark.
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yeap till it starts to overflow , maybe i have a vacuum leak. i been doing research and this seems to be the only way. i mean new tps and clean maf and a brand new denso O2 sensor. i dont know what else it could be . i know a tune up would help but i know if i was to do it now i know my mpg wouldnt return to normal. how can my car just drop from 23 to 11. thats a big drop
Posted: Sun Jul 29, 2012 9:32 pm Post subject: fuel mileage
just wanna throw this out there,but cant believe it would make that much difference, but how are your tire pressures? Any brakes dragging? I don't know what else to attribute this too. I'll ask around and keep thinking.
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Yeah, check you tires and all your fluids. Also, idk about 3400's but 3800's don't really like other brand oxygen sensors than AC Delco. You're on your original plugs and wires? Its probably time to change those as well.
When you cleaned your MAF, I'm hoping you used MAF specific cleaner.
Maybe you need your pcm to recalibrate before it will start running properly. There is a procedure on this forum somewhere about the cylce (its like 5 mins at 50 mph, 3 miles at 35, etc, its kinda complicated). My gas mileage was horrible when my cat was clogged, maybe you have a blockage in the intake or post combustion still. That's really the only experience i've had with really bad gas mileage. Good luck, also maybe changing the plugs wouldn't kill you, at least check them.
Also thinking about it, the front 02 sensor might be throwing a code because there is excessive unburnt fuel in your exhaust caused by a misfire. Unburnt gas blows cats and usually the unburnt gas is due to a misfire, Just a thought.
2001 Impala LS 81k as of Nov,2011
3.8 V6 3800 Series 2
tires are good and you wont believe this but the sensor was a denso sensor. i was getting bad gas mileage before with the old one but this new one is better . although better im still sure i wont get that 330 miles back from changing it. i unplugged the map sensor and will see how it runs . i did use crc maf cleaner , yes plugs and wires are original never changed . fuel filter is as well , i know i need to change that. could a vacuum leak cause this much trouble. im really baffled this is happening.
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