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2011 Dodge Grand Caravan, P0306 (Misfire)

1362 Views 6 Replies 3 Participants Last post by  FreundlichM
Hello! I've posted before about this issue, but I feel that I didn't provide a lot of information regarding it. So, I'm hoping this provides the right information (and isn't too long to read)

As a recap, I have a 2011 Dodge Grand Caravan Mainstreet, which I received from someone else with 174k miles, this was back in 2021. The issue? it came with an engine light on. So, I took it to my old mechanic for it to get diagnosed and it had three codes, a P0306 (cylinder 6 misfire), P0300 (random/multi cylinder misfire), and a small EVAP leak code. He replaced all of the spark plugs, and that lessened the issue, with P0306 and P0300 remaining (intermittently, now)

Awhile back, I took it to a new mechanic who did various tests, concluding that my compression was fine, and that my spark plugs, fuel injector, and coil pack was fine (I changed it myself towards the beginning of owning this vehicle.) However, they did notice that my lower intake manifold gaskets were blown, so they replaced them. This left me with an intermittent misfire on Cylinder 6, that has further lessened in its severity.

However, none of this completely fixed the misfire. So, this being my only vehicle, I hoped for the best and kept driving it (it's at 185k miles, with a bit of a less misfire, and yes, the Catalytic converters are still fine, nor has any other symptoms developed.). I noticed that my misfire was intermittent, and only happened occasionally (I can't figure out when it does happen, it's completely random to me). And I decided to look at my Obd-II scanner. I'm not sure if the fuel trim values are normal (I have attached some images below). Funnily enough, when I'm not misfiring, my idle is smooth, and I experience no vibrations. When I do misfire, my idle ranges between mildly and very rough, depending on the day.

Some important stuff to note. Firstly, I only feel this misfire at idle, and around 30-40 mph, it'll act up whenever the engine is at 800-1,300 rpm, and it'll immediately go away outside of that. And secondly, I don't hear any weird noises from the engine, especially not any ticking/knocking.

I'll list every part changed/diagnosed below:
Fuel injectors - After I took it to my new mechanic, he said the fuel injectors were fine. However, I did find a new fuel injector box in my engine bay, which makes me believe that he did change it.
Coil Packs - Confirmed to be fine, no issue with them (I did replace Cylinder 6's coil pack, to no avail)
Spark Plugs - Changed when I received the vehicle, helped a bit
MAP Sensor - Replaced because the first one was super clogged, so I felt it was better to just buy a new one, no changes.
Resonator/Throttle Body Rubber Seal - Replaced due to being excessively worn out, you could literally put your finger in between the resonator and that rubber fitting. It did help a bit.
The Engine itself - A compression test was done on my engine, and the mechanic stated that the compression was in the normal ranges for every cylinder on it. So, I'm guessing that means this isn't much of a valvetrain/engine issue itself?

I'm not sure to what's causing this issue, and I'm currently building a savings for the worst-case scenario when I do take it back in to get diagnosed.

As I said above, I have attached some pictures of the fuel trim, I believe they look a bit off but I'm not an expert on this. If there's any more information I can upload from my scanner that could possibly help with this, please let me know!

Any help would be appreciated! Sorry for the long post. I'm not even sure of how to tl;dr this.


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Always get those mixed up. :p That's why I prefer O2 delta numbers.

So rich could be a valve not opening enough because of a rocker issue. I know his mechanic said there isn't one, but we don't know if he really knows. Lots of mechanics think the rocker tick is just loud injectors.

Could also be a clog in an injector causing dribble instead of spray.

Partially clogged cat will hold the exhaust gases near the O2s for longer. Loose exhaust can be making the other bank seem rich.
I did recently develop an exhaust leak a bit past the first resonator, so I'm sure that can contribute to the issue a bit. However, would a rocker still cause an intermittent misfire? I'd imagine it'd be constant. Or, could VVT have a play in a rocker issue being intermittent?

Also, I did have both the upper and lower intake manifold gaskets replaced, I forgot to mention that. My bad!
It would be fairly consistent, but not necessarily constant. VVT shouldn't really affect it.

An exhaust leak past the resonator shouldn't be affecting sensors. I'm talking about head to cat, cat to crossover, and crossover to flex.
So, I looked at my OBD-II Scanner again, and while my pre-cat O2 sensors seem normal (ranging between 0 and 1, what appears to be a constant change), my post-cat O2 sensors stay in the higher value, more towards 1. Is that normal? Or, could this very well be a sign of an exhaust leak near the crossover/flex?
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