P0304 and completely out of ideas....

[Surprisepoptart]

So, I'm closer than I care to admit, to throwing in the towel on this one...

I'm dealing with a rough idle and check engine light. The codes says cylinder no. 4, and that's been verified by unplugging the coil pack.
Give it some revs, and it smooths out around 1000-1200rpm.
Give it any load, (like trying to accelerate) it also smooths out even sooner.

Swapped plugs, swapped coil packs, swapped injectors. Even replaced the ecm.
It's getting spark, I can hear it arcing to the plug if I lift the coil out while it's running.

Passed a compression test, and the valves look intact based on what I could see with a little flexy inspection camera.
I want to do a leak down test next, just haven't gotten to it yet.

Only other "symptom" would be a very slight, somewhat intermittent rattling noise from the front of the engine. I'm guessing one of the plastic timing chains guides retired.

What else am I missing? Could a loose timing chain be causing a misfire only on a single cylinder?
Maybe a wacky crank position sensor? I'm at a loss for what to try next

 

[blackhawk]

What kind of spark plugs do you have installed?

 

[lfhoward]

What if a rocker fell off the #4 exhaust or intake valve stem underneath your valve cover? It has happened before on both 3.7 & 4.7’s. The lifter (hydraulic lash adjuster) that keeps the rocker in place can go slack, and the cam can push the rocker off. You could pull the passengers side valve cover and check, since it looks like you have ruled almost everything else out. If it’s just sitting there, you can pop it back on, and maybe replace your lifters while you have it apart.

Here is a good explanation. It’s on a 4.7 V8 but it is pretty much the same engine with 2 additional cylinders.

xc_hide_links_from_guests_guests_error_hide_media

 

[Surprisepoptart]

Ah, forgot to mention I also pulled the valve cover. Lol

All the cam lobes and rockers looked fine. And I’m running….. I think Champion? I forget which brand, but they’re copper core. And swapping one plug to another cylinder didn’t make a difference.

Just did a leak down test today, and still no results. Had some leakage, but it was in line with every other cylinder I tested. At this point I’m thinking I just need to pull the head and hopefully get a better idea what’s going on in there

 

[KJowner]

If it passes compression test and isn't loosing coolant then I'd hang back on pulling the head.
Check injector wiring & coil pack wiring

 

[DodgeBoy]

MAF sonsor, or bad coil pack. Swap out the coil pack with the one next to it. Since you have already swaped plugs and ruled that out the only other thing could be a bad coil. I did a tune up on our 2010 Libatard and it ran great for two days the got a P-3006 code. Took the coil pack back and they gave me a new one. It has ran fine since (tune-up was three years ago). You said you put in new injectors, the #4 injector could be bad. Try swapping it out with anouther one and see what happens. It also could be a bad injector wire.

 

[MerctheJerk]

I had the same problem, it was the PCM.