I am new to this so and need some help. I am experiencing power loss in my 2011 Hyundai Accent. It has 53,000 miles on it. My engine feels like it's stalling and the check engine light turns on. I ran the code and it says P0303 third cylinder misfiring. I swapped out the third cylinder coil with the first cylinder and changed out the spark plugs. I cleared the code and drove another 200 miles with no problems. The engine started experiencing power loss again and then the light came on again. When I checked it, it said it was the third cylinder again. Since I know it is not the coil or the spark plugs I am at a loss as to what it could be. Any help would be appreciated.

 

Since there is a CEL and a code there is a problem. Why did you think swapping coils would fix it? Take it to a REAL mechanic instead of guessing at the problem.

 

I have the same problem. 2011 Hyundai Accent at 54000 miles is suddenly randomly experiencing a loss of power. Can't go more than 40 MPH and it acts like I've suddenly shifting into neutral. The tachometer stops registering RPMs and it sounds like it's stuck in overdrive. The check engine light comes on briefly, but my dealership says no codes are logged. Once I stop the vehicle and turn off the ignition, it resets. I took it in to the dealership as it's still under warranty 7-22-15 and they still have it trying to figure it out. By the way, all four cylinders were replaced under warranty, right front bearings as well, so this vehicle has been less than stellar. Bought it with 10,500 miles on it, dealer owned at the time and have only owned for 2-1/2 years.

 

Your car should have code(s) stored in computer regardless. The garage dealer should do a compression test to rule this out...since you had work done there. Possible blown head gasket or leaking valves.
Getting a code(s) should give you some direction.
Another possible problem could be a damaged/worn timing belt that is causing your problem??..skipping from missing teeth??
If it's still under warranty, maybe dealership is unwilling to go any further to find problem and correct it...$$$ ???
You may want to get a second opinion from another shop...on your dime, of course. Good luck!

 

After two days and several calls to Hyundai's Corporate Office Tech Support, my local dealership was able to determine that it was a "crank sensor fault." The part replaced was a senor-crankshaft position. Gratefully under warranty, so on their dime. Runs well now and seems "tighter." Hope this lasts. This was a tough one for them.

 

Good to hear that your problem was fixed. A faulty sensor is hard to detect if it works then not work then works again.
My daughter's car stopped moving completely (engine still turned, but would not start) because of a broken timing belt. But prior to this event, the car would throw a code that pointed to the VSS sensor and the car would down-shift to a lower gear from the over-drive gear. I initially changed the wrong sensor (not knowing it was the wrong sensor to be changed) and thought the sensor was no longer the problem each time the car would continue to drop to lower gear and throw same code..???
After the timing belt was changed I looked again closely at the VSS problem and finally found the correct sensor and location...changed it and now all is fine.
The broken timing belt (not a chain in this year/model) threw a 'camshaft' sensor and not the 'crankshaft' sensor.
(Sorry for long post.)

 

I initially thought that the loss of power was caused by a faulty fuel injector.

 

I think there was a misunderstanding here.

If there was a DTC code which said misfire on cylinder 3
Then taking the coil out and switching it with another coil on the engine (third with the first cylinder) would allow one to see if the misfire follows the coil
And that would indicate whether it was the coil that was at fault.
It wasn't a fix but a test. Changing the spark plug at the same time seemed to have cleared the problem for a little while.
Which to me would indicate fouling of the spark plug (or not).


The car could be using the VSS sensor in conjunction with the cam sensor to determine if the transmission is running correctly
On my 2001 Elantra, it uses the ABS sensor on the right front CV axle in conjunction with the VSS. My car doesn't have ABS brakes just the sensor.