Cylinder 3 Misfire after Fuel Pump Inspection


I had taken my car to a Kia dealership for an evap canister recall and to check on the fuel pump for an additional letter I received in the mail from Kia re: low-pressure fuel pump leak extended warranty. They checked the fuel pump port and said it didn’t show any signs of leaking. When I picked my car up, I noticed a small misfire on my drive home. I didn’t think much of it because I’m not too familiar with cars but the next day, while it was continuing to misfire, the CEL came on. I called the dealership and made an appt for a week out because they couldn’t get me in sooner.

Fast forward a week, and my car was still misfiring but literally on my way to my appointment at the dealership, the CEL went off. I called them and told them I was going to reschedule (I was really worried about it not actually being from something they did and then have them charge me).

Now, the car continues to misfire even though the CEL is off and when I read the CEL code, it said it was P0303- Cylinder 3 Misfire. I should also add that the gas milage has gone down significantly.

Could this be because of something they did with the fuel pump? I’m assuming it is just because it started immediately after I picked my car up from them, but I just want to make sure I’m not going in there blind and having them try to charge me.

It could be something they did. It might not. There is no way for us to tell from out here on the internet. It is unlikely you can prove it is something they did.

If you don’t trust your dealer’s shop, you can take this car to any Kia dealer and the warranty will follow.


Ask your shop to measure the fuel rail pressure. I’m expecting it is not within the specified range, probably as an inadvertent result of the prior fuel-pump work… Out of spec fuel pressure can definitely cause misfires. If the fuel pressure is out of spec, they’ll know how to correct the problem.

It’s also possible the misfire is a coincidence, nothing to do w/prior work. Common causes for misfires

  • faulty spark plug or coil
  • faulty fuel injector
  • low cylinder compression.

For single-cylinder misfires, mechanics often swap coils or fuel injectors as an experiment. If the misfire follows the swap, the problem is usually the part that was swapped. The powertrain computer uses a pre-designed algorithm to decide whether or not to turn the cel on when it thinks it is detecting a misfire. For example, the misfire may have to occur so many times in a given number of miles. Your misfire may be right on the deciding edge of that parameter.

No, don’t do that. It breaks the cardinal rule that the customer does not tell the shop what to do. It is far better to ask if the fuel rail pressures are acceptable and what they are. The results are the same, but the customer hasn’t alienated the shop personnel.



As a shop, it will tick you off if a DIYer keeps telling (asking) you how to diag your vehicle, do it more then once and they might just tell you since you know more about it then you can Do It Yourself…

If you have to keep making suggestions to the shop checking your vehicle out, then you need to find another shop…

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UPDATE: apparently it was the spark plugs. i am going to replace them tomorrow but i’m so mad at myself for not trying that first before being charged a $180 diagnostic fee

You could also still have an ignition coil (COP) issue, so if the same code comes back then swap cylinders with the coil to see if the misfire follows assuming you have COP’s, I don’t remember seeing the year, model or engine size…

sorry i thought it saved! its a 2018 Sorento, 2.0L turbo engine

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