200k miles. 2010 ram Hemi. Well maintained. Been a flawless truck. New spark plugs 5k miles ago. Uses a little oil between oil changes but always has.

3 days ago, after driving 200 miles, back out of sonic drive-in, cranked the wheel, engine died. Barely would turn over. Drove to parts store, checked battery, said was bad, replaced, back to normal. 2 days later, I get about 100 miles out, and when climbing a hill, it starts to shake and misfire (first time ever). Check engine light blinks 10 times. Get back on flat ground, I put the throttle to the floor, everything fine. Climb the next hill, same problem. Noticed I’m carrying 37 lbs of oil pressure (not sure if relevant) when I usually carry 52. Will change oil/filter (Mobil-1 synthetic) and look for metal.

This morning, fire it up, decide I’m going to try to blow the engine up, and take it for a spirited drive. Carrying 52 lbs oil, and I cannot make it misfire. I can rev to 5k with zero issue, extremely smooth. Would a weak alternator cause an issue?

Zero mechanical noises. No ticks. Before I start tearing and diagnosing what is wrong, any advice on the main issues to start with? Thanks.

 

What spark plugs did you install? How old are your oxygen sensors?

 

Autolite iridium xp (xp5325). I believe I gapped them to .045 when I did them October 2022.

Factory oxygen sensors.

 

Hhhhmmm.... I believe Mopar calls for standard copper plugs in your engine, do they not? I know on the older engines, using rare earth spark plugs tended to lead to mystery misfires, and various other interesting problems. At 200K miles, I would also be real tempted to replace the upstream O2 sensors. They don't last forever. NTK or Denso sensors only though, those were OEM suppliers, and the 'other guys' don't always play nice with the dodge computers.

 

Plugged in and the code is a cylinder 3 misfire. Swapped the 3&5 coils, and swapped the 3&1 spark plugs. Same issue. Also swapped oil filter to a mopar, seems to be a little better oil pressure. Same problem. I fired it up and runs fine. Let it get to operating temp and still fine. Revved it multiple times and it’s fine. Take it on the road and several miles later it finally starts to misfire. Bring it home. Shut off. Turn on. Can rev and idle with no misfire. I’m going to pull the valve cover and if I don’t find anything I’ll probably go back with the oem style spark plugs. If still nothing, maybe pcm

 

Swap 3 and 5 injectors before you tear anything else apart. See what happens.

 

Swapped 1&3 injector. Same issue. I’m leaning towards the pcm being bad. It will not misfire/throw a code until I hold it at or above 3k rpm. Runs smooth at idle and if I do a quick rev. If the pcm fixes the problem, I will be back to update.

 

Have you monitored the short term fuel trim when the misfires are happening, or checked the freeze frame data for when then misfire codes have been set, to check for any consistencies? Since it's somewhat random, I'd be more inclined to think you might have a manifold gasket that leaks at certain temperatures or something similar. An unmetered air leak may show up in the short term fuel trim numbers.

 

I just have a cheaper code reader. Not sure it has the capability to read for that. Should have a new pcm delivered hopefully by Wednesday the 28th. I’ll know then. I’ll be putting a dial indicator on a few valve springs to check for lift If the pcm doesn’t fix it. Been a great truck, averages 20 at 60-65, and about 17 at 84.

 

New pcm did not fix the issue. Going to be tearing into it for a cam/lifter set. I can’t complain, 204k miles, this truck has never left me stranded, and it still looks brand new. Debating whether to upgrade the camshaft now..