2010 Kia Forte intermittent misfire under load

Hi, I have a 2010 kia forte with the 2.0 theta engine. I am getting an intermittent misfire on cylinder 1 under load, usually around 40mph it will happen. Although I have gotten p0304 before as well but it mostly seems to be p0301, I am assuming because it is the companion cylinder.
When viewing the misfire data it does not always feel like it is missing. I can feel it once the check engine light starts flashing, and sometimes it will stop and other times it will continue until you restart the car.
I have replaced spark plugs, swapped the coil and spark plug, cleaned the map sensor, new injectors and fuel sending unit (there was a high ltft, knock sensor code, and fuel filter was pretty dirty). Also checked compression and I believe cylinder 1 was highest at around 240 and cylinder 4 was lowest around 225 (I'm thinking my gauge reads high).

I got some secondary ignition waveforms for cylinder one after a short drive (using the probe connected to a penny taped on the top of coil, so not sure how accurate they are). Misfire data indicates misfires occured around 50 seconds, 1:30, and 4:30 in the video. At 1:30 the check engine light was flashing, and the waveforms look pretty crazy. Can anyone help make sense of these?

Thanks!

watching the capture after a while there you’ll see the end of burn line jump up really high. This signals a lean misfire.
I’ve included a screenshot of your video to show you what I mean.
Power brake it and with the scope if you can.
I’d move toward fuel.

That's what I was leaning towards after researching, thanks for the conformation. What do you mean by power brake it and with the scope? I will try swapping the injector though. I wish I could test fuel pressure but adapters are too expensive for this car. If swapping injectors doesn't work then I'm guessing the new fuel sending unit is no good. Either that or ecu isn't sending the injector signal. I guess I could add that to the second channel. Or maybe the ecu is turning the injector off when it sees the miss?

Power brake/brake torque is holding brake while in drive and giving it some throttle.

In this case where you have single cylinder miss I wouldn’t think fuel pump right away. That would have an all cylinder effect. Swapping the injector is a good idea.

Can you lower the time base for a more detailed capture? I want to rule out worn cam lobes.

It looks, to me, that your Firing and Spark lines are both low. (maybe just a characteristic of the Penny-probe) How is the spark plug gap? Can you post a waveform of a good cylinder to compare?

I agree with John Curtis on the Lean/No-fuel mis-fire, too.

I'm gonna be that hater and say you may still be dealing with an ignition problem. :lol: I completely agree that the high 'tail' at the end of the burn line screams lean. BUT, I really don't like the strong coil oscillations that come after. That coil is RINGING. :silly:

Have you tried any swapnostics on your replacement coils/plugs?

If I end up being wrong, you can tell me to STFU.

John Curtis wrote: Power brake/brake torque is holding brake while in drive and giving it some throttle.

In this case where you have single cylinder miss I wouldn’t think fuel pump right away. That would have an all cylinder effect. Swapping the injector is a good idea.

Can you lower the time base for a more detailed capture? I want to rule out worn cam lobes.

I will try swapping the injector, and if that doesn't help I will try power braking it and using a lower time base.

Chad wrote: It looks, to me, that your Firing and Spark lines are both low. (maybe just a characteristic of the Penny-probe) How is the spark plug gap? Can you post a waveform of a good cylinder to compare?

I believe that is just due to the penny probe, as another cylinder looked the same. I will get a waveform from a good cylinder. Spark plug gap is good, about .042" I think.

Tyler wrote: I'm gonna be that hater and say you may still be dealing with an ignition problem. :lol: I completely agree that the high 'tail' at the end of the burn line screams lean. BUT, I really don't like the strong coil oscillations that come after. That coil is RINGING. :silly:

Have you tried any swapnostics on your replacement coils/plugs?

If I end up being wrong, you can tell me to STFU.

Yeah those oscillations were pretty concerning.. I'm wondering if the ecu is shutting off the injector when it starts missing/mil flashing? Misfires at around 50 seconds in the video did not cause mil to flash.
I swapped the coils and plugs with no change.

I swapped the injector and took it for a short drive. It didn't really act up, although there were a couple misfires on all cylinders this time, but still mostly cylinder 1. I didn't have time to do anything else. And got a p0326 knock sensor code. I should probably scope that to determine if it's actually the sensor or something else, maybe related to the most likely lean issue.

Haven't had a chance to look at this or even drive the car, but it doesn't seem to be missing but still has p0326 knock sensor code. I tested the knock sensor and it seemed bad, so I replaced it. But I am still getting the code. Tested wiring between sensor and ecu connector and it seems ok (4ohm). Here is a video of the knock sensor with some power braking in there, it looks ok to me so I am really at a loss as to why it would be giving this code. Also I found another scanner to see the lftf and it was ok now, around 5% if I recall so it doesn't seem to be a lean problem.