2012 3.6L Dodge Grand Caravan weird compression waveform and misfire

Hi All,
Longtime lurker and SD subscriber here.
I was hoping I could get some advice on a strange looking cylinder pressure waveform.

Background:

My mom had me look at her van today for a check engine light.
It had a P219A (Bank 1 Cylinder Imbalance) and a P0301 code.

At first glance, it appeared that the fuel trim on bank 1 was correcting based on bank 2.
I took it for a test drive and the vehicle would begin to misfire under heavy acceleration. I couldn't really feel it, but the MIL was flashing.
After coming back to idle, I could at times feel hesitation, but never a dead misfire.

After the test drive, I cleared DTCs in order to look at the true fuel trim data.
Bank 1's short term fuel trim would sometimes exceed 20%, but other times be under 10%.
I noticed the poor fuel trims at both idle and under load.

After that, I swapped cylinder 1's coil and spark plug with another cylinder, and took it out for another test drive.
During a WOT runup it began to misfire again (as indicated by the flashing MIL).
The scan tool indicated that it was still on cylinder 1.

Next, I did a quick compression test on cylinders 1 and 3.
I began to doubt my gauge because cylinder 1 maxed out my gauge at 200 psi.
Cylinder 3 was closer to 160 PSI.

I have an old vantage meter and pressure transducer, so I took a look at both cylinders and saw a strange looking waveform for cylinder 1.
I am thinking that it may point to a collapsed lifter causing the exhaust valve not to open fully. However, I am much more comfortable diagnosing electrical concerns rather than engine concerns.

Disclaimer: I am not a mechanic by trade, I am a part time Engineering student that works in the automotive field, so this type of thing is more of a hobby for me.

With that being said, if this looks like an engine mechanical issue, I will need to pay someone to do the work since my time is very limited. I'd like to have a good idea of what I'm dealing with beforehand.

I've attached 2 pictures for cranking compression on the bad cylinder and a good cylinder.
I know they are terrible due to the glare, and the goal of capturing them was more to gain a qualitative assessment, as well as to double check my compression gauge.

Does anyone think that my suspicion is correct?
Do you have any suggestions for other tests I could try?

Thanks in advance.

I think you're absolutely on the right track with a mechanical issue. Unfortunately, this engine is well known for valvetrain issues, including failing cam followers and wiped cam lobes. Either one would account for your misfire. An intake pulse waveform might be fun? But I don't think it'll tell you anything you don't already know.

There's some extended warranty coverage from Dodge on these engines, but most of it centers around bank two. May be worth a call to your local dealer anyway. Worst case, they say no.

If you're intent on proving a mechanical issue, then the next step is pulling the bank one valve cover. It's not a hard job? But it doesn't just fall off, either. :lol: Don't forget to pull the PCV valve out of the rear of the valve cover before trying to pry the cover off.

I am somewhat confused about your waveforms. The good cylinder, #3, should be able to do more than 113 PSI cranking. I'm wondering if you're going to find more than one problem if you take the valve cover off...

Is it possible that maybe the exhaust header is clogged or restricted for just that one cylinder?

I've never seen a pressure wave form like that before. Assuming that this engine is no variable displacement ( I don't know if it is or not )... during cranking, I think it's only possible for a cylinder to increase above normal pressure if exhaust is not able to fully escape, right?

The exhaust manifolds for this engine aren't really manifolds - the three exhaust ports all merge into one before leaving the cylinder head. The exhaust manifold is really just one big pipe headed to the catalytic converter. So, an exhaust restriction on one cylinder is unlikely.

No variable displacement on this engine. I agree that you're likely looking at an exhaust valve(s) that has insufficient lift/duration. A VVT sprocket that was stuck retarded might have the same result? But that'd impact the whole bank.

Firing Order: 1 2 3 4 5 6

I suspect compression on Cylinder #3 is bleeding over to cylinder #1.

Now there's an idea, Chad.

That should show up with a leak down tester, no? OR, hakuchi could repeat the in-cylinder for #1 with the #3 plug removed. That'd should result in a normal-er waveform, and doesn't require access to compressed air.

Man, I wish I would've thought to do that test!

Unfortunately, we have to send it somewhere since I don't have the time or expertise to do engine work like that.
I should find out tomorrow. I'll update the thread when I do.

Thanks everyone!

Go into cylinder #3. An in-cylinder, running compression waveform will show compression loss. Due to the leak/loss of air, the vacuum pocket after the expansion stroke will be deeper than the vacuum of the intake stroke.

Tyler wrote: That should show up with a leak down tester, no?

That's what I would do...roll #3 up to TDC compression, pressurize the cylinder with shop air, and listen through cylinder #1 spark plug hole.

I just wanted to update the thread. The vehicle was taken to a reputable local shop, and they continued with the diagnosis.
They removed the cam cover and found the intake cam was worn.
The vehicle just finished up today, and I am told that it drives much better.

I am kicking myself for not getting a better waveform capture, and I'm shocked that the problem was found to be with the intake and not the exhaust cam.

Either way, thanks again for the insights.

Thanks for the update. I'm glad the problem was resolved.

I'm having a hard time understanding how a worn intake cam lobe would would make that waveform. A worn intake cam lobe would make the valve open late, not open all the way, and close early. That would cause low compression, for sure. But, how is it seen in the expansion stroke, when all valves are closed? Any thoughts?

Thanks for the update!

I think that you are going to find that if it was indeed a worn intake cam that it was not the whole story.

A worn intake cam can't explain this in any convievable way that I can think of.

The only way that could even possibly happen would be if the intake valves were normally still open during part of the compression stroke. I don't know why this would be the case ( because it would waste power and lower compression ).

But IF that were the case... a worn intake cam would cause the intake valve to shut early, increasing compression at low RPM's only.
At high RPM's the late opening of the intake ( due to the worn cam ) would restrict airflow too much. But at low (especially cranking RPM) sufficient air can still get around the intake valves (even when they open late ).

This is just a thought though. It is the only possible way that I can think of that a worn intake cam could increase compression.
I doubt very seriously that this is the case.

You'll probably continue to have issues with it.