So my 2006 with a 4.7L magnum which I bought back in Nov 2019 with 122k recently developed an issue where it throws an engine light for a misfire on cyl 8 when it's cold/first started and I immediately put it on drive and attempt to go. It even bucks a little. But if I let it idle and warm up a bit, or raise the rpms to say 1200 and hold it there for about 10 seconds, or give it a few rev's to 1200 or so a few times, the roughness goes away and the engine light doesn't come on.

I swapped the coilpack from cyl8 to cyl7. That made no difference. I then swapped fuel injector 8 with 7. Still no difference.

In Dec, I changed oil and used full synthetic 5w-30 at 125k
In Jan, I changed spark plugs and used OEM champions gapped to .040" at 126k
Yesterday, I changed the PCV since the original one was caked in dirt and probably had never been changed. I wasn't expecting it to fix my misfire problem on cyl 8, and it did not.

On a side note, I also hear a ticking sound when cold coming from the left bank area but it goes away once the engine warms up, and it's been that way since I bought it back in October. I cant tell if it's an exhaust manifold leak or a lifter.

I know a misfire can be caused by lack of spark (bad coil or plug)
I know a misfire can be caused by lack of fuel (clogged/faulty injector)

But I've swapped the coil and injector and yet I still get the misfire on cyl 8. And I would think that if either the coil or plug or injector were bad, I would have the misfire even when the engine is at normal temps. But I only get the misfire/rough running when the engine is cold and I start it up.

Can a sticky/faulty lifter cause a misfire?
Would a sticky/faulty lifter function normally again when the engine warms up?
Is seafoam worth a try?
Should I take the valve cover off from the left bank and plan on replacing all 8 lifters?
Is there anything else to check for that can cause the misfire on cyl 8 only when the engine is cold and I start it up?

Once the engine is warmed up, there's no misfires or ticking and it runs great.

Any help would be appreciated.

 

Not to be a downer but the 4.7 engines are known for top end issues. Especially lifter issues .I’m a mechanic and love my dodges, but I’d never buy a 4.7 because of what I’ve seen in the shop....best bet is to remove valve cover and inspect

 

Ok. I was going to save doing that for last, but it doesn't look like too much work to do. Just time.

Based on the symptoms I've described, what do you think I'll find?

Can a sticky lifter be cause for misfire on cold startup?

 

may be fuel pressure regulator in the fuel pump assembly. May be fuel pressure bleeding off when you shut the vehicle down. I had an 03 4.7, no starting or driving issues. Couldn't get the CEL to go away. The new fuel pump fixed it. Might be worth a shot testing the fuel pump.