I have a 2012 2500 4x4 with a 5.7 Hemi. With 130,000 miles. Under hard acceleration it misfires. It's throwing codes 300,305,307. I replaced all 16 plugs and coil packs on # 5&7 with dealer parts. Any help would be appreciated.

 

Bad fuel was my issue. Just for fun start filling up with chevron or some other name brand super. After a couple tanks see if the condition goes away. But for sure use a different gas station and brand.

I was having only one cyl misfire, you are having two which is more of a concern, but still a few tanks of quality gas might help.

 

I doubt its a fuel issue if the same exact cylinders are mis-firing every time.
Sounds like a faulty electrical connection, or a bad sensor. (crank angle sensor...?)
Should check the fuel pressure as well... plugged fuel filter...? pump going away...?

 

if not a mechanical issue, then most likely the injectors are not spraying a good pattern. Sometimes running better quality gas like Chevron with Techron will improve the pattern and the misfires go away. You can try the Techron concentrate for a couple of tanks and see if it helps, or, have an injector cleaning service done.

 

Valid point pedro... the cheapest way out is the best way out, if it fix`s it.

 

What Pedro said. Obviously gas won't fix an electrical issue, but in my case the same cylinder kept misfiring. I ran a tank of Chevron super, and then a couple tanks of 89 from a different station closer to home. Problem disappeared.

Coincidence? Possibly. The dealership was at a loss as to what was causing the issue so gasoline was the last resort before tearing big things apart. No misfires since.

 

This is what I would try 1st. Do a seafoam clean. Get a couple cans. About $8.00 per can. Put one can in gas tank(read directions on mixing ratio). Take the other can and do this.Run engine till hot and leave running while doing this. Pull the vacuum hose off you brake booster and slowly let the suction from the brake booster hose pull the seafoam in from the can. Let it sip it,do not chug it and use about 1/3 of the can. The turn engine off and let sit about 10-15 minutes. Then start engine and watch all the smoke come out of your tailpipe from the carbon that has built up in the engine. After smoke has let up somewhat take it out for a spin. It will still smoke somewhat depending on how much gunk your engine had in it. But take it out and drive it at hwy speeds for a while. 10-15 minutes. Then drive for a day and do it again if needed.

I have been doing this seafoam treatment for over 25 years. I had a chev pu back in the 80s that always had a miss. Never could find the cause. Replaced everything. Took it to shops and they could never get the miss out. The seafoam did the trick. Been using it ever sense and it's one of the things that actually works.

 

Nice way to plug up the cat converters. Couple tanks of techron or gumout "all in one" will do a far better job over time without filling the cats with carbon.

 

In doing this over the years I have never had a prob. with catalytic converters going bad. It's a myth. I know many peoople that have done this and I have never heard of a problem.

And No,techron or gumout will not do the same thing. You sound very uninformed.

 

Seafoam has a much higher concentration of unicorn tears, thus no cat converter damage. Sheesh, I thought everybody knew that.