FIXED Really need help 2017 dodge caravan 3.6 with cylinder 2 misfire

It’s my wife’s van, 2017 Dodge Caravan with the 3.6 engine. Check engine light came on, I have a handheld scanner at home just to pull codes, it was a P0128. It’s at a 100k so I cleared the light and scheduled to bring the van in for service about 6 days later. During the 6 days the light came back on, I assumed for the p0128, so I didn’t check it. Got the van in changed the thermostat and when I went to clear the codes I noticed a p0302 misfire code. Again it’s at a 100k, I remember already doing the plugs and coils once a few years back, decided to do them again since we have a trip coming up. I used OE plugs, Champion Iridium, and Duralast coils, the intake takes 10 min to pull of that. Fired the vehicle up and felt like it was still missing slightly. Connected scan tool and sure enough it was still missing.. I did an induction service and that seemed to take care of the miss. Took it for a test drive and just before I pulled up I noticed it missed twice.. pulled it in and now I’m starting to notice it still feels like it’s missing but the snap on Zeus wasn’t picking it up. Hooked an vacuum gauge to the intake and notice it was low and steady 15-16 inhg.. I did an engine cranking sound test and it didn’t sound clean at all.. I have a feeling this is going to make me pull my hair out. I drove it home let it sit over night, got in it early in the am and did another cranking sound test and it sounded perfect. The miss isn’t easy to feel sitting in the vehicle but looking at the engine while it’s running you can def see the engine has some shutter to it.. I have a 20 min commute to work, pulled it in, checked misfire data and sure enough still missing. Did another cranking sound test and again it wasn’t good. So seems to run ok cold, cranking sound test is good cold, all of that changes once it’s hot… it’s only cylinder two that has the miss. I read on Mitchell under secondary ignition circuit that the pcm cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing, or open spark plug cables. The misfire will however increase the oxygen content in the exhaust, deceiving the pcm into thinking the fuel system is too lean. Fuel trims (LT) on both banks are a little negative, -4 to -5 percent, -7 to -8 percent under a load and ST trims stay at zero or go slightly positive 2-3 percent however my bank 1 rear o2 sensor stays below .450. .095-.113. I assumed that sensor was lying, after inducing propane all 4 o2 sensors went rich, over 800 ml volts for the rear and front were 3.4 v maybe even slightly higher.. Again my miss is on bank 2 cylinder 2 and that lean o2 is bank 1 so I doubt it’s related,Im just giving as much info as I can.. The miss is constant, again you can’t feel it but you can def see it in the engine, vacuum isn’t very good, not sure why our scanner isn’t picking it up consistently, but it’s not, it jumps up to 10 -20 misfires, then drops down to zero as if the misfires stopped hit my vacuum gauge and my eyes tell me the miss is def still there… I also don’t understand why cranking sound test is good cold but bad hot? Maybe it’s not maybe it’s bad on both just more noticeable when it’s warm.. Any help would be appreciated and sorry for the long write up..

I've seen more than a handful of those with valve train problems. Since you have a Zeus, I think you should start with a relative compression test.

Not sure I did it on the greatest settings but any thoughts?

Def looks like there’s a dip/gap in there.. maybe I’ll pull the intake again when it cools, pull all the plugs, get a spec and a pressure gauge and get readings on all cylinders..

I can def feel a miss but again it’s not that bad. Part of me says it’s def a mechanical issue but it’s running so well for it to be a mechanical issue… It’s not throwing any codes, it accelerates fine and the misfires according to scan data come and go, however, again my vacuum gauge is reading 16-17 inhg at idle, turn the a/c on and it drops about 14-15 when the compressor kicks on then jumps back up when it turns off.. (is that normal?) I’m still waiting on it to cool so I can check compression..

Indeed the RC capture shows a repeating pattern with one cylinder low.

When the ac-compressor engages the rpm are commanded slightly higher to compensate for the additional load on the engine. A wider opened throttle will affect intake manifold vacuum.

As you measured vacuum with a real gauge:
is the needle stable or does it flicker/bounce regularly while idling?

As you don't notice lack of power:
is the miss present at idle only?

If so it might be a valve(train) issue which is not uncommon on this engine as Noah already mentioned.

XsleepercellX wrote:

Not sure I did it on the greatest settings but any thoughts?

Definitely one low cylinder there. What probe were you using, and where was it connected?

I'd add a sync to your next capture so you can ID the low cylinder before pulling the intake again. Pick one of the rear bank coils and connect a backprobe to one of the coil control wires.

Valvetrain issues are indeed common on this engine, and usually shows up as a misfire at idle like you've described. Smoked cam followers and flat cam lobes are typical, but I've also seen leaking intake valves several times.

The amp clamp I use.. I attach it at the battery neg cable, 40 amp setting on a 5 sec screen. Not sure that my settings are great but I’ll def try tapping in to ca coil control wire on opposite bank and do the same test to see where I’m at..

Here’s some info about how Chrysler detects misfires, anyone have any ideas on how to use this info in a diagnostic situation would be helpful. My thoughts are to pull the intake and spark plugs, get an actual compression reading in all cylinders and I’m also thinking I should pull the valve cover off and visually inspect the valves, valve springs, lifters, rockers and cam lobes for cylinder number two. Before pulling the cover though, if I do have low compression I’d add oil and recheck, if ok I’d do a leak down test and then from there depending on what I find, pull the cover and just inspect what I can visually… it’s not making a ton of noise so I don’t have high hopes it would be something easy like a bad lifter or rocker arm.. I’ve seen people just loosen the cam enough to pull the rocker arms out without messing with timing..

Sorry for the blurry pic. I can type what it says here.

P0302
Based on the signal from the from ckp the pcm has detected a misfire in cylinder 2.

DO NOT CLEAR THE CODES! It is very important to understand how Chrysler products detect misfires. They use a value called the Adaptive Numerator. This is a learned picture of the ckp pattern taken during a fuel shutoff deceleration event. With the fuel injectors off, the crank is just spinning on its own so the pattern is clean. After 3-4 of these the numerator is learned. The running pattern is then compared to this. When a miss occurs, the pattern is longer due to the crank slowing down when it should be speeding up. The cam sensor is used to determine which cylinder is missing. If more than one cylinder is missing, p0300 is set along with the individual cylinder codes. When a misfire code is set, the pcm turns off the injector. No injector plus is a result of the miss, rarely is it the cause. If it is the cause , you will have injector codes as well. If you clear the codes or reset all the adaptives, the pcm will lose the adaptive numbers for and will not be able to test for a miss. You will need to relearn the numerator be performing the freeway speed decals until the scanner shows that it is learned. The pid for this can be hard to find. Sometimes it is in the data list with all the other data, sometimes you will need to access the “which cylinder is misfiring” test to see it. Once your repair is complete, then clear codes and do the relearn procedure. Then you can verify your repair.

Definitely pull the intake, get a compression value for all the cylinders, then leak down test to confirm the nature of the fault.
I have pryed the rockers out and reinstalled without loosening the camshaft or timing, if that is the issue. At my shop, I have even seen them put a rocker in an engine that really should have gotten a camshaft. There was noticeable scoring of the lobe but misfire codes did not return and the customer is satisfied with the repair.

Ok, pulled the intake and did a compression test. All cylinders were @145-150 psi except cylinder number 2 which was right 100 psi and the spec is 100 psi.. I added some oil to the cylinder and the compression jumped up to 150 psi… Looks like it’s piston rings which sucks…. Not sure if the engine has to be pulled for this repair or if it’s doable from underneath just removing the oil pan, if anyone has experience with swapping out piston rings on this engine feel free to chime in and let me know. Thanks to everyone that pitched their ideas, it was all much appreciated..

XsleepercellX wrote:

Ok, pulled the intake and did a compression test. All cylinders were @145-150 psi except cylinder number 2 which was right 100 psi and the spec is 100 psi.. I added some oil to the cylinder and the compression jumped up to 150 psi… Looks like it’s piston rings which sucks…. Not sure if the engine has to be pulled for this repair or if it’s doable from underneath just removing the oil pan, if anyone has experience with swapping out piston rings on this engine feel free to chime in and let me know. Thanks to everyone that pitched their ideas, it was all much appreciated..

Do a leak down on cylinder #2 anyway. I can't say that I've ever seen (or even heard of) a bad piston ring on a Pentastar engine before. Not saying it's impossible, just rather not see you go down the lower end repair path needlessly.

Tyler beat me to it, I would still do a leak down test.

You talked me into it lol.. I’ll take the intake off again, it’s not a big job any way and I’ll perform the leak down test.. Now that you guys mention it, it’s making me rethink the test I did. I used transmission fluid instead of oil (hope that’s correct, if not let me know and lesson learned) aside from that I’m certain I put too much oil (trans fluid) in the cylinder. Normally I like to get 4-5 compression strokes and record my pressures. After adding the trans fluid, I got three compression strokes totaling 150 psi and the engine stopped cranking on its own. Red lighting volt on the dash was flashing on me, I turned the key off, tried to start it again, this time my compression gauge was disconnected and nothing, no starter engagement at all. I disconnected the battery for a few minutes, hooked it back up and it started cranking again. I was worried I may have done more damage like a blown head gasket or worse, bent valves if that’s even possible so I was eager to get it put back together and make sure I didn’t do more damage, on top of that I was upset with the reading. I ran it and made sure it’s not running any worse or blowing out white smoke. Once I was in the clear, I started questioning the amount of fluid I used asking my self if I could rely on that test or not. I know carbon can cause higher than normal pressure in a cylinder because of the amount of space it takes up, so I questioned if I put too much oil in the cylinder would it not have the same effect? Idk, just rambling my thoughts, but I’ll do the leak down test and get back with results as soon as I’m able to do so.

are you able to circle the wave capture and show me the misfires?
how would I determine the firing order based on this capture?
how do I dissect this waveform?

In the future, don't use ATF in cylinder for wet compression test. Apply engine oil instead.

Mechanic 350 wrote:

are you able to circle the wave capture and show me the misfires?
how would I determine the firing order based on this capture?
how do I dissect this waveform?

Without a sync from a coil firing event, you can't for sure. In hindsight, knowing that #2 is having lower compression, we can infer the low hump in the pattern is #2, then plug in the firing order from there.

Every time I have had a pentastar 3.6 with a Misfire on cyl#2 I pull the valve covers. Rocker arms /roller followers fail almost religiously on cyl two first. Just remember to remove the PCV valve from the rear of the right bank valve cover along with the actuators on the front over the cover and cam sensor on top.

Pulled the intake off against today and the valve cover so I could be sure my lobes weren’t opening the valves and it has a little bit of air leaking past the intake valve seats and a pretty decent amount of air leaking past the exhaust valves.. I put a rubber glove over my tail pipe and it filled the glove like a balloon…. I’m gonna guess an say I should just pull the head, slap a new one in and be done.. Def beats a new engine.