So been trying to figure out what’s causing this misfire. Figure before I go as far as taking the head off I could use a little advice on what to check next.

My truck is a 2003 Ram 2500 with the 5.7 and auto transmission. The misfire code is from cylinder 6. I only run premium gas in it which is 91 octane up here. Never been over heated. You can hear the misfire at idle bit not noticeable on hwy. In fact some of the work I did on it I would reset light and see if it comes on again and on two different occasions I had different results. If I drive it about 25-30 miles in town it will turn light on. If I hope on highway it takes about 200 miles before it turns on. Very odd to me and I’ve stopped driving truck for moment until I can figure out this misfire out of fear that it will damage itself further and leave me stranded.

What ive done so far are:
-replaced all 16 spark plugs
-replaced all wires
-swap some of the coils around
-ran several different injector cleaners through it(including a full bottle of lucus that’s for 100gallons)
-did a compression test on the passenger side and results were cylinder 2 (135psi) cylinder 4 (130psi) cylinder 6 (122psi) cylinder 8(118psi).
-replaced air filter
- replaced throttle body (randomly had the throttle stop working with that lightning bolt light flashing was hoping the misfire would go away with that but no luck)
- Battery and alternator(my alternator had sparks shooting out back of it and battery was only at 40% life so replaced it with new one at same time)

Any help on where to go next. Any sensors stand out that could cause it? This weekend I’m thinking of taking valve cover off and running air through cylinder to see for leaks but not sure if it’s worth it since the compression isn’t too far off. It’s always been my faithful truck and have never let me down until now. It fired up like nothing this last winter at -35 without wind and no block heater.

 

What spark plugs are you using?

 

I believe they are a/c delco platinums.

 

I'm pretty sure the general consensus here is that the hemi runs best with original champion coppers. Maybe do some searching. Also believe I have read other guys have had issues using different plugs...you could maybe buy 2 coppers to try in the cylinder that's not happy???😮

 

Look at box from a friend’s tune up and thought it was mine. The 16 plugs I have in it are autolites number 5263. I’ll try swapping the two with champion coppers this afternoon. My friend with his 4.0 jeep says same thing about the plugs. Now that I think about it I should have treated the 5.7 like the 5.2 in my last Ram and that one only ran right on the cheap coppers. But anyway I’ll try the two plugs this afternoon and report the result to see if more digging is needed.

 

These trucks tend to HATE Platinum plugs. Go with Copper Plugs.

 

Sounds like it’s idling a bit better but still hear a bit of a missfire in engine bay and the engine still shakes still to where you can feel it in cab. Once warmed up you can hear the popping in that cylinder a few feet away.



Right one is the one attached to coil. Plugs only had 2k on them.

 

Maybe think about pulling valve cover on that side? ? Check for broken valve spring ?? Just an idea...

 

That’s what thinking at this point tomorrow is take valve cover off and take a look. Then if I can’t see anything hook up compressor to that cylinder and see if maybe a valve seal is leaking. Kinda hoping I’m over looking something simple but deep down I think there is an issue with the head. Yes I’m in denial. Lol

 

Not just a river in Egypt any more.

You may be able to rent a bore scope from your local parts store. Or even buy one off Amazon for cheap. Poke it in the spark plug hole, and see if anything interesting presents itself.