Okay y'all, so I'm trying to help my son diagnose a transient misfire. Unfortunately he's in Austin, and I'm in Houston.

Vehicle details:
2012 Ram 4X4, 5.7L, 165K miles

Misfire details:
Codes:
P0307 #7 Misfire Detected
P3450 Deactivation / Intake Valve Control Performance

Other than the misfire, the engine is smooth and powerful. Idle is steady and even. The misfire occurs when under significant load or heavy acceleration, generally above 4K rpm. Occasionally will occur below. Check engine light will flash, and engine will misfire. Misfire will clear out in 2-5 minutes if driven easy.

He changed the #7 coil and plugs, and ran some Techron through it, with no change.

Thinking (hoping) its the cylinder deactivation solenoid (or associated wiring) that's giving him his misfire, and NOT the dreaded chewed up camshaft/lifter issue.

I'm having him pull the valve cover and check for rocker arm movement. After that, I'll probably make a trip out and pull the intake for a look around and maybe to change out the solenoid.

Thoughts?

 

I highly doubt camshaft failure if there is no noticeable valve train noise. Possible broken valve spring only showing up under higher rpm ?? Im kinda doubtful of cylinder deactivation solenoids as well.
I think I would swap coil packs from another cylinder first. ( I know you said you already replaced) . If code for cylinder 7 still comes up swap injector from another cylinder. (or jump right to injector swapping first). If code rears its ugly head on 7 yet again at least you have cylinder 7 to focus on....coil or injector wiring or mechanical. Just my thoughts.

 

Son here,
Decided to switch out coil pack for cylinder 7 with cylinder 3 (mainly because it was the easiest to reach for me). Truck started up beautifully, made it about 5 miles with zero misfire. Then I got the truck up to about 3800rpm and boom the CEL flashes and stays on. I had the codes checked again and I'm now getting the same cylinder 7 misfire (P0307), the same P3450, and a new cylinder 1 misfire (P0301). I've now looked at the coil packs and cylinder placement about a thousand times and I'm positive it was cylinder 3 and not 1....I never even touched cylinder 1 coil pack. Anyone have any idea as to how this could make sense?

 

Not making any sense to me either. unless there is a wiring issue. I think I would pull a valve cover to inspect valve springs for cylinder 7....seems as its still throwing that code

 

Yep, gonna pull the valve cover, see if we see a popped spring. While we're in there, we can confirm cam lobe integrity. Keeping my fingers crossed.

From there, it will be additional testing of wiring, coils, plugs, and injectors. Then finally, under the intake for the MDS solenoid.

Still at a loss as to why we would have a misfire on cyl 1 after swapping coils between 3 and 7. LOL

 

Only guess I could make....if intake valve spring broken on 7, possible unwanted turbulence and exhaust gas made its way back into intake manifold causing misfire on 1. ?????😑

 

Been thinking about your issue a little more...as I just went thru diagnosing and replacing a camshaft in a 2011 5.7.
Again I highly doubt mds solenoid failure. When MDS solenoids activate, oil pressure is blocked to the appropriate lifters. The lifter bleeds down to the point where the valve will not open and the lifter basically just goes for a ride around the cam lobe. You could try driving the truck and manually shift gears without going to top gear. It is my understanding that MDS will not activate until high gear. If you still get a misfire at 3800 rpm in 3rd gear for eg. That would eliminate this cycle of the mds.
Now if you had a stuck MDS solenoid always blocking oil pressure to lifters I would think you would get a misfire well under the 3800 rpm.

 

TrueDogman,

Thanks for the effort in helping us out with this. One thing that I failed to mention, that may play a part in this, is the fact that the truck was way overdue on the latest oil change, and was low on top of that. So, let's assume some gunk/build up.

If that's the case, what if the solenoid is 'fouled' with sludge, and can't return to full open, allowing good oil pressure to the lifter? Or at best is inconsistent?

Thoughts?

Oh, and my son confirmed (again) that he swapped the 3 and 7 coil packs. Still getting an misfire on 1 though. That almost makes me think 'wiring harness'.

We're gonna tear into into it tonight, so one way or the other, we should have some answers.

Thanks again!

 

The PCM controls the coil firing. It is a direct connection from the coil to the PCM connector. Look around there.

 

Yep. After thinking about it some more thats quite possible as well. When I removed the MDS solenoids they were rather corroded into the block. After removing a lip of rust I drove a couple screws into the plastic solenoid and used a slide hammer equipped with vice grips to pull on both screws to pop them out. 3 of the 4 broke. (Did a MDS delete). If memory serves me correct there was a small screen in the bottom of the solenoid which I supposed could get plugged. The lifters for the 4 cylinders which run MDS also have small holes which I suppose could get plugged.
Im with others too thinking you may find a wiring issue.
Let us know what you find. Good luck !