Question about 2001 Hyundai Elantra

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Poor acceleration, poor gas mileage

I have an 01 elantra. It is getting about 19 mpg highway. Sometimes when i hit the gas it revs to about 4000 rpms but doesn;t really move very fast. also when i am in the 60-70 mile per hour range it has no accleration. there is no check engine light and i just past inspection where the mechanics said they could not find the problem while driving it. It almost feels like an old car with the ac loses power, but mine happens with the ac on or off. I have read about 02 sensor, fuel filter and maf sensor...all of which are supposed to throw a code...any ideas?

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  • mighkey Aug 19, 2008

    thanks, so i need the upstream o2 it something i can do, not much under car experience. I have read about torque settings and and some sort of treatment for the threads....

  • mighkey Aug 20, 2008


  • cploliveira Sep 25, 2008

    I have the same problem same car year and model.Mechanic looked a *** and said I needed to replace the cat converter and o2 sensor. Taking it there this week and I will post the outcome for u.Hope it fixes it because I couldnt afford a new car and had already had replaced the motor and radiator already so Im invested. I will never buy a Hyundai again, I had a ford escort for 11 years and it didnt give me half the problems this car has. Good luck.

  • Anonymous Nov 23, 2008

    Had the same prob. with my sister in laws car. I changed both o2 sensors and that did not work (-$200). One mechanic told me it was the catalytic converter. So... not knowing there were 2 we replaced the front one (assuming it was the only one.) This did not work (-$271). By this time I was mad enough to pay the $90 charge for a dealer to diagnose the problem. He told me it was the 2nd catalytic converter. So we took it home and removed the 2nd converter and found the inside of the first converter had broken up and was lodged in the 2nd converter. Replaced the second converter (-$250) and it runs like new. Keep in mind I did the work myself, so the money spent was just on parts!!!



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I have the same problem as talked about above. 2002 Hyundai accent gsi. HORRIBLE gas mileage. I only get about 320 km per full tank. My driving habits are good. i took it to the garage and they put it on the computer and no error codes showed up. Question: Can a MAP sensor be faulty but NOT show up on the computer diagnostic? I had my O2 sensor checked out and my exhaust, and changed the flex pipe. Car runs pretty good just horrible gas mileage and kinda crappy power. Changed fuel and air filter. Cleaned the fuel system entirely ($80 at garage not $4 bottle).

Anyone ever use a resistor in the MAP sensor?

Posted on Nov 19, 2008


Try changing the MAP sensor
my hyundai ran really bad and skiped and cut off then i change that 45 dollar part and now i get 350 mile to the tank in town.

Ryan S

Posted on Aug 25, 2008

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O2 sensor is the most likely problem - the one before the catalytic converter, not the one behind it. Also, get electrical contact cleaner and clean all the sensor harness connectors you can find underhood. Finally, run a Seafoam treatment (Seafoam is available at parts stores) through the car, and see if that takes care of it.

Posted on Aug 18, 2008

  • Jeremy Dellow
    Jeremy Dellow Aug 19, 2008

    You don't really need to worry about torque settings for an O2 sensor - just get it in there nice and tight. You could put some anti-seize on the threads to keep from rusting the sensor into place though. You'll need to buy an O2 sensor socket to remove and install them though - the wires on the sensor preclude using a normal socket, and an O2 sensor socket has a cut on the side to allow the wires to be free of damage.

  • Jeremy Dellow
    Jeremy Dellow Aug 20, 2008

    A failed primary O2 sensor could potentially cause an emissions failure because if it fails fully, the car would revert to preprogrammed fueling maps that would cause it to run excessively rich. It might fail for that, or over time it could fail because the excess fuel would clog the cat. The secondary O2 sensor is the main one for emissions control (that's its entire purpose), so a failure of the secondary O2 sensor would definitely cause an emissions failure. The primary could, but won't necessarily.


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