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I recently bought a used 2009 Hyundai Accent because its supposed to get good mpg. I noticed it wasn't getting as much as I expected, so I filled up the tank and drove until empty, and I got an average of 20 mpg. This is way lower than it is supposed to! I've only had the car for a few weeks. What could be the problem?
 

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I'm not getting the MPG I thought I should be getting-- I mean, honestly I haven't calculated what i'm getting, i'm just comparing to my other car the interval between getting gas.

I'm thinking it's mostly my driving style, although next spring I plan on changing the spark plugs.
 

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oh boy another post about elusive fuel economy...i gotta write something up about this so i can copy and paste.

try these in roughly this order:

- if you are all city driving, your mileage will be low. nothing can be done about that.

- if you drive hard, you FE will be low.

- check tire pressure and alignment. *severely* out alignment can cause FE drop.

- if you carry around heavy stuff like tools, lose that.

- code scanner is exactly correct. most problems related to FE will be stores as error codes in the ECU even if not engine light on. those are called pending codes and require multiple occurrences in a row to notify you.

- disconnect battery for 20 mins if no codes. modern ECUs try to learn your driving habits and adjust...they don't always do it so well. this will reset and start over.

- now time to get under the hood. check plugs, wires, intake/airbox blockages, broken/cracked vacuum hoses, leaks, etc. fix any issues you can see. i recommend testing parts such as wires. not everyone does, but i don't believe replacing parts at random is doing the job right. plugs and air filter are dirty cheap and wear out anyways...so yeah replace those.

- note condition of old plugs when you remove them. look up a spark plug troubleshooting pic on google and compare. if not the usual tan colour, it can indicate something is going on.

- check belts. a slipping belt represents a loss of energy.

- keep up on the regular maintenance. oil changes ignored can add extra friction in the engine internals. same with transmission fluid if you're rockin the auto trans. when was that last done? whats your mileage?

- check for dragging/stuck brake calipers. there's an easy one.

- as a last resort, try going somewhere else for fuel if you usually go to the same gas station. unlikely cause, but why not scratch that one off. even do that first if you want, easiest one here. don't waste your money on higher octane fuel. it will not help.

- don't waste your money on engine and fuel injector cleaners. they aren't going to help you for this or any other problem. if you're concerned, clean out the throttle body with a brush and carb cleaner, pull out MAP sensor and check if its clean, check PCV valve to see its clean, and so on.
 

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Auto Trans? If it popped the overdrive bearing it'll be stuck in 3rd but won't trip engine light, and 20mpg would be about right.
Easy enough to tell, get it up to highway speeds and click the O/D Off button on the shifter. Should jump the RPMs up, or Vice Versa. Have O/D off and then click it on and watch the RPMs drop.

My GF CONSISTENTLY drives with O/D off because she prefers the lower shift points and she still gets about 26~29 mpg mixed (but mostly off highway) from what I can tell. So even if O/D bearing was borked I don't think MPG would even be as low as 20. Just my opinion tho.
 
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