5.7 has the sniffles

[Darthomas]

Posted a thread on B bodies but I guess
I'll ask here since there are new hemi owners. 103,000 mi 2013 ex Michigan State Police Charger 7000 hours on engine and 5000 idling.
Great price. #2 cylinder "funny".
Changed:
Plugs ( had very hard black deposits)
Coil Pack (by Mich St Pol previously)
Fuel injector
Engine control module (as I had noted weak signal to injector during misfire).

No better.
Many applications of Sea Foam and Marvel Mystery Oil and there was a change. Instead of a big miss under load at 1500 rpm, THAT went away and became a light roughness at lower speeds.
I think the exhaust valve got stuck in one spot, and now it's rotating, but landing on a seat of hard carbon that only fits well and seals efficiently in one spot.
So I have driven a thousand miles since the change and while I want to believe a rotating valve will eventually clean off the carbon on the seat and itself, I've never had this situation before. I know that anything that "partly heals" is good because something real like a burned valve or seat never gets better.
It definitely is smoother now at idle and while it does still throw P203s, especially right around 1500 rpm, it is doing it less.
So the question:
Let's say this valve didn't rotate for 6000 miles. If it built up deposits on the seating faces, and didn't burn the valve or seat,
how long do you think it might take for normal rotating operation to beat the deposits off to where that valve seals better?

j

 

[Map63Vette]

Have you ever tried really wringing the engine out with high rpm high load stuff like a drag race? Getting the combustion chamber good and hot might help to loosen up carbon if that really is the problem, though I'll admit it's a gamble. Running a rough running engine hard is more likely to break something if there is a bigger issue going on.

 

[Johnny Mac]

The Good thing about these engines it they are all O-ring, and fairly easy to work on.
The bad thing is all the factory stuff is TTY.

If it were me, i'd pull that head, and see where i was before wailing on it, or putting more mystery goop in it. Sometimes things like the lucas oil additive can do some "cool" things like re-pop lifters and such...but sometimes you just gotta see what's going on. The engine bay is pretty open on the LX. for the price of a head gasket and a set of tty head bolts, i'd probably pull the head while it's a "head" problem. Before it becomes a " dropped a valve and busted a piston,which then sent pencil shavings through the entire bottom end" problem.

If you go this route, and a local dealer wants an arm and leg for the parts let me know, I can get you an OE head gasket and head bolts pretty reasonable.

 

[mechanicmark]

I would do a compression test first, both sides.

 

[Darthomas]

No can do at present.
Life went kablam after divorce,
working off the debt living in a friend's apartment.
I've done all kinds of work but can't in an apartment lot.
Plus I'm working 6 and 7 day weeks.
I have thrashed it fairly well, the valve did not rotate until major chemical treatment and thrashing.
Now I gotta baby it until I get into a house.

 

[sam65]

No can do at present.
Life went kablam after divorce,
working off the debt living in a friend's apartment.
I've done all kinds of work but can't in an apartment lot.
Plus I'm working 6 and 7 day weeks.
I have thrashed it fairly well, the valve did not rotate until major chemical treatment and thrashing.
Now I gotta baby it until I get into a house.

 

[sam65]

pull the valve cover and have someone crank the engine while you watch the rocker arms after unplugging coils.I chased a problem like this it would idle fairly well and as soon as you started accelerating misfire code and cel light flashing.turned out it had the lifter wheel locked up on intake lifter wiping the cam out,it had compression and all the other stuff it needed to run cranking.the almost flat cam would open the valve enough cranking to show good compression,but running it wouldn't open the valve enough to get fuel for load above idle.I found this after I had already pulled the head and put it back together only to pull the head again to change the cam and lifter!!

 

[Darthomas]

In the first two weeks, the miss would show up, and turning off the engine and restarting made the idle damn near perfect.
This was 100% of the time, so it was sitting in one spot, I think and if didn't fall exactly in line with the built up carbon it didn't seal well. It could be a wiped lobe, but I wouldn't expect that to be a variable condition.
I've read about bringing the piston up on the compression stroke, pulling a plug, filling the chamber with Sea Foam and letting it stand overnight.