I recently changed my timing belt and water pump on my '03 elantra. After the job, my car seems to run fine, no noticeable difference in power, no sputtering, idles smoothly etc. However, my gas mileage seems to be worse than before I changed the belt. Thought maybe I was just being paranoid, but I've checked it carefully over the last few weeks and there really does seem to be a noticeable change, about 5mpg lower than it used to be, both when I take an average over a tank of gas as well as when I set cruise control and look at the trip computer. I have checked tire pressure and other potential simple answers.
Is it possible that I got the timing off by one tooth? if the belt is off one tooth, i would think that I would notice some performance/power differences beyond just gas mileage. Anyone have any experience with how an elantra might perform with the timing belt one tooth off?
The timing system is very precise regarding fuel trims (fuel map). If the timing is, in fact, one tooth off, I'm surprised you haven't had a 'Check Engine' light with the DTC of P0016 - Crank position to Cam position Correlation and P0010 Camshaft Position-Timing Over-Advanced or System Performance(Bank 1). This condition will definitely affect fuel efficiency - no doubt about it. You can verify this by checking the ECU fuel trim data adaptives (OBDII scanner) - they should be near 100% (or zero '0.0'). You might also get a P0171 or P0172 - System too Lean or Rich.
Long as you got the gear marks in the right spot you good, but if you got the mark of 1 you have fuel problems
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