In-depth look into p0300

[MP9C]

Hey everyone, First post here due to my newly acquired Ram.

Specimen on hand
2011 5.7 Bighorn
190k

Maiden voyage was 2.5 hours across the state pretty much without issue.
Ended up with a o2 sensor code for a bad sensor and a P0308 for a bad coil. The old sensors looked original so they were all replaced, and a new coil was needed on cyl8 all was good.

The next day I ended up with a P0300 and I have been chasing it ever since “roughly 2 months”

So the P0300 consist of misfires on cylinder 4 and 6

I have changed plugs, changed coils, cam sensor, crank sensor, Intake gaskets, I have pulled a valve cover to look for broken springs, damaged rocker arms to find nothing damaged.

I have also rotated the motor over by hand to measure the max lift of the cam through the rocker ratio from the rocker boss in the head to the peak of the rocker arm and they all measure the same So I am assuming the cam is fine.

I have also pulled the pushrods to make sure that nothing was damaged or tweaked to find nothing.

Also rotated injectors and the miss didn’t move.

Compression is 175 175 160 190 so yeah I know 6 is the weakest but it’s still within spec I also performed a wet compression test and all cylinders are over 300psi so that should rule out a bad seat or a burnt valve

I did notice while testing and running the engine, when it’s missing the worst it seems the coils on 4,6 have lost their - pulse trigger from the pcm

So just replaced the PCM had it updated with the most recent flash from Chrysler and had everything re-calibrated to the new PCM for it to not help at all.

I even added a heavy ground from the engine to the chassis wondering if that would help.

So when cold it runs great, once warm at an idle it sucks but if you stay driving at a normal pace or Highway it runs perfect but in stop and go it’s a mess.

I have done a lot of testing thus far but I am looking for any insight that anyone might have.

Thank you in advance.

 

[MP9C]

Ohh I also replaced the MDS solenoids in the block for 4,6 wondering if they were messing with it and replaced the VVT while I was there too.

 

[Dodge 1500 4X4]

Did you do a leak down test that will check your Rings and valve seats for each cylinder, did you replace all the sensors with OEM style also any metal in the oil, cut your filter open and check it out, you replaced your VVT solenoid was there any metal in it?

 

[MP9C]

All sensors were replaced with OE mopar, I do not have a leak down tester but the compression test is within spec if there were major damage they wouldn’t be as high as they are. An in theory the wet compression test will test for damaged valves or seats because the pressure rises if the chamber is sealed. If you had damaged parts the pressure wouldn’t go up.

 

[MP9C]

VVT screens were clean and no flake at all in the oil.

No real hemi tick either, tho I am wondering if the lifters are just starting to bleed off or developing an issue on those 2 cylinders. Or wiring is messed up somewhere.

I am running pretty thin on ideas.

 

[Burla]

Question.

How do you now this?

So the P0300 consist of misfires on cylinder 4 and 6


My guess is the cam is worn right to the point of fail regardless of everything pointing away from it. Most of the metal was likely flushed long ago, probably the very reason the dude sold the truck.

 

[MP9C]

I know it’s 4,6 because I can see the livestream data in the pcm and watch the misfire counters.

 

[Burla]

It's rare, but have to looked at combustion chamber and maybe see if you have a lot of carbon perhaps hinting at worn rings? The fact you have two sources of misfire, it could be some widespread wear through piston rings on an aging engine.

 

[MP9C]

I did run a bore scope down and the pistons and walls look good but I couldn’t really get a 180 view to see the actual chamber.

I would think rings that worn would show on the compression test, something crazy ya know sub 100 psi

 

[MP9C]

Another odd thing I noticed was if you are stopped at an idle and it starts to miss bad, most of the time you can turn the truck off and start it right back up and it runs a lot better for a bit again but will go back to missing the next time ya stop.

 

[Burla]

Oil PSI maybe? very rare but can cause a misfire. when cold you are good, usually psi is up then, but when warm psi usually lower, maybe? How low is psi getting at warm idle? lower then 35? you running 20 weight oil? you can try a 0w40 maybe srt oil, should boost psi.

 

[Mister Luck]

Injector clips ?
and or harness ?
Weak fuel will lean out the cylinder and create wear you said you traded the injectors you can’t trade the clips

Did you check Fuel pressure at the fuel lines up to the injectors or cylinder temps on 4/6 ? , lack of fuel would make 4/6 hotter than the rest. (what color are the plugs for those cylinders compared to 1-8

Ever perform a coolant system pressure test ?

 

[MP9C]

I have been thinking about how it runs to relative oil pressure but haven’t charted it yet.

I rotated injectors twice to see if I could get any variance, hence removing them from the rail and moving the actual injector location. All wiring is still in factory condition.

I have tested the injector circuits with noid lights to verify they are cycling and they always do regardless of it missing or running smooth.

I had to order a fuel pressure kit due to it not having a test port, I hope to have those numbers today.

Plugs have been in decent shape anytime I have pulled them. No color fouling no green no signs of burning coolant and I am not loosing coolant.

 

[Jwithing]

Good luck. Im subscribing to see what comes of this. I've been having the same issue with cylinder 1 and 7. Cylinder 7 acting up more with one starting intermittently a bit later. Also have P0219a air/fuel imbalance as well that is permanent. P0300, P0301, and P0307 are able to be cleared but don't always popup together. Typically get a cel after 1k miles or a warm engine restart followed by quickly getting on it. Been going on for about 15k miles with 102k miles on the truck, but I haven't really noticed any performance degradation or pinging.

I replaced mostly the same parts as you except for cam and crank sensors since the truck freaked out when I replaced the crank sensor because they need to be programmed, which I didn't realize. I did replace the map, iat, pcv, 02 sensors, and two new injectors as well. Pulled the vvt solenoid and confirmed no shavings when I did the 6.4 manifold swap. Also pulled the valve covers and didn't see any play in the valvetrain or unusual valve travel. Haven't done a compression test yet, but at this point I'm leaning towards running it till it pops, then putting an mmx 6.4 longblock in it.

 

[MP9C]

It seems odd to me that the problem cylinders with these trucks just happen to be the MDS cylinders
Bank 1 1&7
Bank 2 4&6

Odd or coincidence hummm ?

 

[Burla]

disengage mds with shift *** or tow haul and see if you still get misfire code.

 

[Dodge 1500 4X4]

I wonder if under a load#4,6 lifters are losing their prime causing a misfire, like you said you shut down the engine and restart it you have good pressure Like Burla said disable MDS or put it in tow haul, put a mechanical oil pressure gauge on it and you'll know what the oil pressure is.

 

[Mister Luck]

Valve springs tension on those cylinders weaken because they become thermal heat sinks from inactivity during ECO ?

intake manifold plenum needs servicing ?

 

[MP9C]

Well it’s single digits outside and snowing so I didn’t get to test anything yesterday.

But I went for a good 1.5 hr drive taking the dog to the vet. So I decided to 2 foot the whole way and holding the idle when stopping around 700rpm just above where it would idle on its own and it makes a huge difference no codes on that drive.

So I am thinking it’s pressure related!

Possibly those lifters on 4,6 are bleeding off.

I did try tow/haul or downshift to 5 but that don’t help the idle which seems to be where 95% of the problem is.

 

[MP9C]

So I think pulling the head and doing a set of lifters is probably in my future. My only other short term test option I could think of would be tossing on a programmer and bumping the pcm idle to 700-750 and see how it does. But that would be more of a bandaid on a repair that needs to be addressed.