Ive done just about every test I can find to do chasing this issue and I'm about to start shotgunning parts out of frustration.
I've had intermittent p0306 codes for a while and recently I had a massive overheating issue that turned out to be a blown head gasket on bank 2 as well as a failed MDS solenoid on cylinder 6 and VVT solenoid. I replaced both head gaskets and the MDS, VVT solenoids, found oil in the intake so I cleaned the manifold and replaced the PCV and intake gaskets. I cleaned the heads before reinstalling them. It all went well but on initial start it ran like crap and it dawned on me that I didn't clean the spark plug holes and the plugs were grounding out to the heads because of the fluid covering the plugs. Pulled the plugs, wiped out all the contamination in the sleeves, put in new plugs and boots. Changed oil and air filter as well since they were due. Ran good for a few days then started running really rough at idle throwing p0306 code and smoking out the tail pipe. It smooths out after a bit but the miss doesn't completely go away even at freeway speeds.

Compression test is good, leak down test is good, plugs still look good, MDS is functioning, VVT is functioning according to what live data shows for timing advance at different speeds. I swapped coils with another cylinder and the code didn't change. Noid light shows injector signal is good, resistance test shows injector is good. I will be doing another spark test tomorrow to make sure spark is getting to the plugs since my tester was bad the first time. Unplugging the injector and coils on cylinder 6 doesn't change anything, but unplugging other cylinders does. At this point I'm stumped.

The miss gets worse after sitting for a bit and a nice smoke cloud blows out on start up that goes away but the truck still smells like it's running really rich. Start up reminds me of a partially flooded carburetor engine but it doesn't clear up completely. I'm tempted to unplug both the injector and coil to see if that does anything. I did have a catalyst efficiency bank 2 code but that went away and hasn't come back. I'm not sure what to do other than start replacing parts. One thread mentioned a stuck open injector but that should show in a resistance change when testing the injector I would think. I doubt I would have good compression and leak down tests if metal from the screens on the old MDS solenoid was clogging the oil passage but not too sure about that part and can't really find any info on it.

 

What color smoke?

Have you tried swapping the number 6 injector with number 4? The injector can 'test' good, but, still be problematic.

 

Smoke is white/grey mostly. Just for the hell of it I put in some Lucas oil injector cleaner yesterday. After about 50 miles driving the truck smoothed out and the CEL went off but the miss didn't go completely away. Frustrating

 

Will your scanner show you misfire counters? If so, (or, the code comes back) I would still swap injectors, and see if the miss moves with the injector.

 

Code has come back this morning along with p1416 which prompted the MDS solenoid replacement.

All wiring checks out fine so I’m down to replacing the injector and now I’m thinking a sticky lifter or partially blocked oil passage since the old solenoid screens were toast. Really don’t want to tear off the manifold and head again without some kind of confirmation. I do have a good inspection camera in my tool kit so I can pull the plugs and look into the cylinder.
I did another compression test/leak down test on cylinder 6 and it was good. There is also a squeaky chirp sound when the miss is at its worst but I don’t think that has anything to do with it.

only other possibility I can think of is a breech between the pcv part of the intake and cylinder 6 intake port since they are right next to each other. Spraying starting fluid around the intake didn’t cause a change so it would have to be an internal crack in the intake manifold.

I’d take it to a mechanic but several I have gone to don’t want to touch it due to having 290k miles on it. They all want to push a new engine swap at a cost of around $9000. I did pull the oil pan to replace the rear main seal a few months back, checked all rod and main bearings while I had it off and they showed very minor wear. The truck is fine other that this dam cylinder 6 issue.

 

If you end up going in there again, might be tempted to do the MDS delete.....

 

All moot now. Engine is toast. Something went haywire and knocks everywhere so time for a new truck since I need it for my business and can’t afford the down time to swap engines right now being the busy season. I might put a new engine in it at some point or sell it as is but for now the 8k plus it will cost will go to another truck.

with 291k miles on it I figure the transmission will need a rebuild soon too.

thanks for all the advice

 

Given the mileage, a new truck probably isn't a bad idea. The engine had a good run, the trans probably isn't far behind, not to mention every other part on the truck that you haven't replaced yet......

 

heh just did front struts and tires a week before this happened. Axel and hub bearings 5 months ago. Been a good truck. In fact all my dodges 91 Dakota, 95and 97 rams hav all lasted 300k miles give or take.