Misfire

Welcome to 2CarPros.

That is high RPM's for highway driving. I hate to ask this, but were you driving really fast? I only ask because I'm concerned that the transmission may not be shifting into the highest gear. Let me know that.

Next, has the check engine light come on while the engine is running? If it has, you really should scan the computer to see what diagnostic trouble codes are stored. Here is a quick video that shows how it's done:

https://youtu.be/YV3TRZwer8k

I realize most people don't own a scanner, but most parts stores will do it for free or lend or rent one to you.

Let me know.

Joe

Welcome back:

It could be fuel related. It's interesting that the exhaust tips have gotten black fast. Often times, black residue or smoke indicates a rich fuel mixture. However, that should set the check engine light.

The engine should not be near 4,000 RPM's at the speeds you mentioned. Does it seem to be shifting normally? At 65 mph, I would suspect them to be around 2000 to 2500.

I don't know if you are interested in checking the fuel pressure, but here is a link that explains how in general it's done. You will need a fuel pressure gauge, but most parts stores will lend or rent one to you.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are the specific directions, pressure specs, and general trouble shooting tips for your vehicle. The pictures correlate with the directions.
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Fuel Pressure Test

1. Release the residual pressure in fuel line .

CAUTION:
When removing the fuel pump relay, a Diagnostic Trouble Code (DTC) may occur. Delete the code with the GDS after completion of "Release Residual Pressure in Fuel Line" work.

2. Install the Special Service Tool (SST).
(1)Disconnect the fuel feed tube from the delivery pipe.

CAUTION:
There may be some residual pressure even after "Release Residual Pressure in Fuel Line" work, so cover the hose connection with a shop towel to prevent residual fuel from spilling out before disconnecting any fuel connection.

(2)Install the special service tool for measuring the fuel pressure in between the fuel feed tube and the fuel delivery pipe .

pic 1

3. Inspect fuel leakage on connections among the fuel feed tube, the delivery pipe, and the SST components with IG ON.
4. Measure Fuel Pressure.
(1)Start the engine and measure the fuel pressure at idle.

Fuel Pressure:
480 - 500 kPa (4.9 - 5.1 kgf/cm2, 69.6 - 72.5 psi)

NOTE:
If the fuel pressure differs from the standard value, repair or replace the related part .

pic 2

(2)Stop the engine, and then check for the change in the fuel pressure gauge reading.

Standard Value:The gauge reading should hold for about 5 minutes after the engine stops

NOTE:
If the gauge reading should not be held, repair or replace the related part .

pic 3

(3)Turn the ignition switch OFF.
5. Release the residual pressure in fuel line .
6. Test End
(1)Remove the Special Service Tool (SST) from the fuel feed tube and the delivery pipe.
(2)Connect the fuel feed tube and the delivery pipe.

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Let me know if this helps. Also, let me know if the RPM's were as high on the way home for you and if the transmission seems to be shifting through all the gears.

Take care,
Joe

Welcome back:
I'm glad to hear you got it going. As far as the injectors, they can get dirty, but any that you would purchase can do the same thing, so I don't think it's a problem with the factory ones.

As far as the timing, I believe this engine has a chain, which is less likely to give you trouble. However, refer to the owner's manual. If it indicates anything about servicing or replacement, do it. All Hyundai engines are referred to as interference engines. Basically, that means if the timing goes out for whatever reason, major internal engine damage is usually the result.

Let me know if you have other questions.

Take care,
Joe