I got this 2017 used last year with 101k on it. It's been pretty good. It consumes about a quart of oil every 1000 miles but I monitor it closely. I had the plugs and coils done about 7 months ago after a misfire. The mechanic said the plugs were fouled. Everything was fine after that until now.
I was driving one day and felt a shudder around 40 MPH. Thought it was the transmission so I changed the fluid. But it kept getting a little worse ...happening at around 20 MPH and at 60 MPH. This was intermittent so it didn't always happen. Also the check engine light popped on and stayed on. Then a few days later day when it was happening the check engine was flashing. So then I knew it was a misfire. I took it to Advance Auto and they scanned it. It came back with codes for Random Misfire and Run Lean. I checked for vacuum leaks but there was nothing obvious. Didn't smoke test it or anything.
I drove it for another week and it got progressively worse. I didn't always flash with a misfire in that time but overall It was getting worse and became to unsafe to drive because of lack of power, so I took to the shop. They told me the high pressure fuel pump was no good. But it was $1100 for the repair, so I decided to take it home and order one and do it myself.
Well I replaced that along with the tappet roller underneath it. It's right on top of the engine and was very easy. After replacing it the car runs the same. No power when accelerating. Just doesn't really want to go. It's always idled fine though. So at this point I have no idea.

 

There is a path that takes place when different things are not working correctly.

When the plugs became fouled, resulting in misfire(s), that has an effect on the converter (s) in the exhaust system.
If due to contamination they become restricted, it WiLL result in a power loss.
Somebody is missing the boat here and it might be a good idea to have qualified shop diagnose the problem.

 

Thanks. I'm going to take it to a Hyundai dealer and pay for a diagnosis. Then take it from there. But yeah, the catalytic converter was something I was thinking of, because even though it idles fine, when you go to drive it the car also sounds like a Go Kart along with not having much power.

 

The tubing connections on the hi press pump are supposed to be replaced if removed for any reason. Those lines are under a few thousand pounds pressure and once the tubing connections are tightened originally ,they form a setting and usually can leak when reinstalled setting up the conditions for an engine fire..

Please notify the servicing facility of what was done..

 

I'm gonna end up junking it. I was gonna bring it in but I don't want to to pay to have it diagnosed when the truth is staring me in the face. The engine is clearly blown. How do I know? It's a Hyundai. That's what they do. Worst car I've ever had by far.

 

Many times it is cheaper in the long run to pay for the repairs for a short while than car payments for a lot longer