terrible gas milage

[kei9th]

i have a 2003 Hyundai accent 3dr 5 speed 1.6 liter dual overhead cam. the car has roughly 155,000 miles on it. sorry i didn't buy American but it was what i could afford ive had this car since 2005 and have all ways gotten at least 29 mpg but mostly around 32-35 mpg. about 2 months ago i started to get bad mileage, now im down to 20 mpg. i changed the oil, air filter, plugs, ran a couple of tanks of high test with injector cleaner. NO CHANGE just terrible mileage. i did have a bad wheel bearing but that has been fixed. no check engine lite. im stumped, i know ill will lose some mpg over time but this has been suddenly and like 10 miles a gallon less. any ideas?

 

[raven7]

Re: terrible gas milage

Maybe a brake dragging? A quick check of your hubs after driving a bit should tell if that's the problem.

 

[Bob_VT]

Re: terrible gas milage

Clean the Mass Air ...... check the tire pressure too

 

[dr_bowtie]

Re: terrible gas milage

that and the O2 sensors...those will kill mileage when they go...

 

[moonfish]

Re: terrible gas milage

that and the O2 sensors...those will kill mileage when they go...

I've heard that about some cars and in them it is common.

 

[kei9th]

Re: terrible gas milage

i know its not the brakes as i thought that first. i did some research and thought it would be the o2 sensor, sometimes i can smell gas when driving but not always. i have 2 o2 sensors one before the catalytic converter and one after the cat, which one would be bad? also wouldn't i get a check engine light if it were a faulty o2 sensor? i have been told it could be bad injectors? i can replace them but the ear on a screwdriver test sounded good. tires are fairly new and just had them rebalanced and rotated because i bought the extra incentive package and thought that might help.

 

[45Auto]

Re: terrible gas milage

Time for a compression check.

 

[j_martin]

Re: terrible gas milage

If you're smelling gas when you're driving, it's leaking. Kills mileage and is one extreme fire hazard, no matter where it's coming from. Modern fuels tend to take out rubber parts in 6 - 10 years.

02 sensor operation can be observed with an ecm scanner. You can also tap into the line and check it with a multimeter. It's supposed to toggle regularly, now stick at one voltage.

hope it helps
John

 

[dolluper]

Re: terrible gas milage

Check for pending codes ....who does it run ....any shaking??? fuel filter replaced since you owned it or timming belt replaced ?? how many miles have you put on it since you got it??

 

[deadstick]

Re: terrible gas milage

have you drove the car since doing the bearing job. bearing could have been binding causing bad fuel mileage.

 

[Bob_VT]

Re: terrible gas milage

The "normal" ECM routine would be to check all the sensors and if one fails it will usually put the ECM into a default mode which hurts MPG but it will also throw a CEL on.

 

[Ken G]

Re: terrible gas milage

I was also thinking a leak on a fuel line or in the tank. Or maybe you have a neighbor with a new siphon hose.

 

[kei9th]

Re: terrible gas milage

i bought the car with 20,000 miles on it and have put 130,000 since ive had it.yes i have been driving the car since the wheel bearing replacement and haven't gotten better millage. i thought about some shady neighbor stealing gas so got a locking gas cap. i dont seem to have a leak cause i parked over top of a refrigerator box and took my wife's car and im not having any leaking spots. ill go to pep boys and borrow the scanner and see if that has any codes.its free so why not try. im just about ready to sell the car and buy a new used, but if i can i would like to fix this one.

 

[Howard Sterndrive]

Re: terrible gas milage

plugged catalytic converter was my first thought, but think the cel would be on, and car would have a definite power issue with plugged converter.
The old Hyundai Excel converters used to have an issue with the innards coming loose, but they only had 1 O2 sensor, so it didn't usually trigger the cel.

Maybe the timing belt has jumped a tooth or two.
150,000 on a timing belt is about 50,000 too much.

 

[kei9th]

Re: terrible gas milage

im gonna do a compression chek. i think if a car jumps a tooth on the timing the car would run rough. my car starts and runs smooth as glass

 

[javsam]

Re: terrible gas milage

The oxygen sensor before the catyltic converter has more of an effect on gas mileage,so that would be the one I would change.

 

[kei9th]

Re: terrible gas milage

thanks everyone im gonna change the o2 sensor and ill report back

 

[dolluper]

Re: terrible gas milage

So I assume you have never replaced the timming belt nor the fuel filter.....well before you waste any MONEY see if you have any pending codes= codes that have not turned on the light yet.....hope the reader you get has that function

 

[kei9th]

Re: terrible gas milage

no i have not replaced the timing belt or the fuel filter. replacing the timing belt on this car is a weekend process and since its been 95 degrees all day everyday that will have to wait.

 

[javsam]

Re: terrible gas milage

I would start by following what has already been stated.
1. check each wheel for a dragging brake.
2. install new spark plugs.
3. Replace oxygen sensor before catylitic converter (upstream)