cavalier poor mpg

2000 CHEVROLET CAVALIER
55,500 MILES • 4 CYL • FWD • AUTOMATIC
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BAT KID
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hi, i have a 2000 chevy cavalier and it all of a sudden started getting horrible gas mileage. i was getting 26mpg in the city. now i have getting 17mpg highway and lesser than that in the city. i've checked for fuel and vacuum leaks, the spark plugs and wires, air filter,tire pressure and have found nothing wrong. the car runs great and doesnt smell like gas or idle rough. the car runs perfectly normal like it always did but before winter started it suddenly dropped. i have a flowmaster delta 40 muffler on it but i took my calculation of 26mpg after it was installed. i understand the winter takes away some fuel mileage but by how much i lost i think something else could be wrong with it. can you help?
Feb 14, 2011 at 9:02 PM
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JDL
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I'd use a gage and check fuel pressure. Also, check that the pressure doesn't drop like a rock when pump stops. If it drops quickly, check for leaking injector or pressure regulator.
Feb 14, 2011 at 9:37 PM
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BAT KID
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ok thanks. i go to college for auto and i will to a test tomorrow bu i was wondering how to check the fuel pressure because cavalier don't have test ports for a gauge. Do i have to T into the fuel line? if so how
Feb 14, 2011 at 11:29 PM
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JDL
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There is kit that modifies the fuel pressure gage with quick connect fittings, so that it will work with your vehicle. I didn't realize till just now, that you don't have a schrader valve. Yes, you have to tee into the supply line.
Feb 15, 2011 at 3:31 PM
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BAT KID
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ok i tested the fuel pressure and its fine. i also looked for gas smells or leaks by the fuel injectors and there's nothing. i check my spark plugs again and i noticed they are turning white. what could be wrong?
Feb 16, 2011 at 6:58 PM
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JDL
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Any applicable trouble codes? If you check codes yourself, at the least, you would need an obd2 code reader. Some of the national brand autostores used to check codes for free. Next, I'd want to see if system is running rich or lean and why?
Feb 16, 2011 at 7:07 PM
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BAT KID
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i used a scan tool in my auto class and nothing comes up for anything but for the BCM code u1000 pops up. im just getting a little confused because the car is getting bad mpg, runs perfectly normal but the signs of the spark plugs are showing that it's running lean
Feb 16, 2011 at 10:15 PM
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JDL
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What are the fuel trims doing, adding or subtracting? Do a compression test. I can't think of anything else, without looking at it.
Feb 17, 2011 at 4:52 PM
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BAT KID
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ok i did a compression test and one on my cylinders had only 70 lbs of compression
Feb 17, 2011 at 8:36 PM
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JDL
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The lowest cylinder reading should not be less than 70 percent of the highest. 100 psi minimum. Could rings or bad valves causing low compression.
Feb 17, 2011 at 9:00 PM
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BAT KID
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ok do you think this could be the problem with my gas mileage? also i noticed the head is covered in oil. and if the spark plugs are white, does that mean the car is running lean? if so would there be a problem with the o2 sensor?
Feb 17, 2011 at 9:05 PM
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JDL
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If all cylinders aren't producing like they should, yes it will effect gas mileage. In closed loop the 02 sensor tells the computer what's going on with the exhaust. If the computer thinks the system is running rich, it will lean the system, that's why I asked you about the fuel trims.

Does the engine use oil?
Feb 17, 2011 at 9:52 PM
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BAT KID
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yes
Feb 17, 2011 at 10:47 PM
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JDL
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Maybe the engine needs an overhaul?
Feb 18, 2011 at 4:26 PM
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BAT KID
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oh god i hope not. i redid the compression test but i accidentally stripped out the hole for the 4th cylinder but i got reading for the first 3 cylinders dry and wet. cylinder #1 was 105,125. #2 was 115,155. #3 was 125, 145. is that bad?
Feb 19, 2011 at 2:25 PM
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JDL
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Doesn't sound as bad as it could be. Do you use more than a quart of oil every 1K miles?
Feb 19, 2011 at 5:11 PM
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BAT KID
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i put four quarts in every oil change which is every 3000 miles. if i ever run low its usually less than a quart
Feb 20, 2011 at 12:10 AM
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JDL
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That doesn't sound bad. Your engine may give you many more miles of service? Whether or not that is efficient service, I don't know?
Feb 20, 2011 at 4:03 PM
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BOBINEHT
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I did a tune up last week on my Cavalier to hopefully fix the problem but it didn't make a difference. I replaced wires, plugs, filters and cleaned injectors best I could. The gas millage went from say 25mpg to 10!! It also is hesitating real bad if I try to push the pedal down during driving. If I let off the gas pedal and slowly press it back down it will pickup and run great again. Can anyone tell me why I would lose so much gas now along with engine hesitating the way it is. It doesn't stall or at least hasn't yet.
Jan 25, 2019 at 6:59 PM (Merged)
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JAYBRIDGES
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Im going to do this in KMs due to me being in canada, but Ive got a 2000 cavalier, i get about 425kms to a tank or 264.082 to a full tank, ive had it put on to a computer that reads codes, firing of the plugs and wires and everything, no codes came up or anything, even read both of the o2 sensors and came up with the right amount of flow. what could it be?
Jan 25, 2019 at 6:59 PM (Merged)
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RASMATAZ
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Could be needing a major tune-up,tires,wheel alignment, suspension, brake and transmission problems-running too rich of a A/F mxture-etc
Jan 25, 2019 at 6:59 PM (Merged)
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JRSSAC
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my cavalier has a pcv hose conected from the valve cover to the intake tube. i replaced stock intake w/k&n typhoon intake system. at the pcv hose connection w/the valve cover oil seaps out and the hose sometimes slips off. there is also oil evident in the intake tube itself. could the pcv system cause excesive fuel comsumption? the haynes repair manuel says there might be blow by or too much crankcase pressure.
Jan 25, 2019 at 6:59 PM (Merged)
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MMPRINCE4000
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PCV simply vents crankcase fumes to intake, if there is excessive blowby, it can cause fuel mixture problems.
Jan 25, 2019 at 6:59 PM (Merged)
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SKITTLEYOU12
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i have a 98 chevy caviler and the gas milage has gone way down. im down to about 10 MPG,when i used to get about 23. do you think it has gone down like this because of bad compression? do you have any ideas for the reason why my gas milage is declining?
Jan 25, 2019 at 6:59 PM (Merged)
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RHALL77
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is the engine running ok? is there a check engine light on? when was the last time you checked your air filter? check and see if it is plugged.
Jan 25, 2019 at 6:59 PM (Merged)
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SKITTLEYOU12
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the engine seems to be running fine but the check engine soon light is on. i scanned the car and it said to check the mass air flow sensor. i checked that and everything was fine. and i just changed my oil, air filter, tranny fluid, and tranny filter.
Jan 25, 2019 at 6:59 PM (Merged)
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RHALL77
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does the engine seem like it has plenty of power
Jan 25, 2019 at 6:59 PM (Merged)
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SKITTLEYOU12
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yes.
Jan 25, 2019 at 6:59 PM (Merged)
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RHALL77
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what was the reading on the data stream when you checked it with the code scanner
Jan 25, 2019 at 6:59 PM (Merged)
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SKITTLEYOU12
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it said there was a problem with the mass flow intake senor. it didnt make much sense on the location of which one it was because its not a V6. but it doent matter anymore because my trnny is going to blow up soon. thank you for your time
Jan 25, 2019 at 6:59 PM (Merged)