Couple weeks ago had the CEL come on for oil pressure switch performance. Scrolled in the VHIC and pressure was down about 10psi from recalled normal - still over 20psi idle and over 40psi cruise. Had an oil change done ASAP and pressures went back to 30/55+.

A week and a half goes by, I'm towing the dakota on my car hauler up a hill and suddenly the truck starts shaking something fierce (like broken rod fierce), CEL starts flashing/dinging. I immediately shut the throttle, everything went back away. I ease back on the throttle and it's all fine and dandy until i put it under load again, all hell breaks loose.

Made it home with the trailer, issue went away for a couple days, could accelerate up on-ramps and pass cars no problem.

The Friday on the way to work, going up a mild grade, it started shaking and tripping the CEL. Did it a few more times, made it to work and home.

CEL is consistently cylinder 3.

Spent today changing the #3 coil, and put 16 new plugs in it. The ones from #3 had more fuel soot on the base than the other cylinders did.

Went for a test drive, and rolling at 2000+ rpm in manual mode was fine. As soon as I went to drive and tried to accelerate on the highway, it started shaking/misfiring, even at 1700-1800 RPM.

I know it's not an MDS-lifter failure. Those are on 1,4,6,7.

But apparently, I wasn't aware that the non-MDS lifters are prone to collapse or lose the roller completely. A collapsed lifter could be fine at low RPM/low cylinder pressure, but fail spectacularly under high RPM. That kind of describes my situation.

It's my daily, so time is kind of crunchy. We have the tools to do it here, but not the time or space. If it's coming apart, I might as well have MDS removed and have my tuner for the dakota tune it out of the computer, too.

Just hoping it doesn't ding the wallet too badly.

 

What year truck? How many miles on it?

 

2011 Ram 1500 (in my signature). About to turn 160,000 miles

 

I think if you lost a roller, the problem would be more consistent. Collapsed lifter seems reasonable, but, it could be an electrical problem as well.....

 

This is where I'm conflicted.

There's no spark plug lead, so I can't check for spark loss with a timing light

I can't unplug an injector and plug a noid light in, because it only happens under load or high RPM

I can't run a compression test because it only happens under load or high RPM

All I can really do is replace the coil, which I have done, or swap injectors, which is a PITA but doable. Because it's normal at low RPM, cruise, and light load, many of the normal/old school diagnostics wont work.

Right now I'm looking at the Mk82 or Scud+ from FRP for $2000 https://frptuning.com/collections/he...41274213695686
And a local trustworthy guy that's done a bunch of DFW hemis says it's $2200 for the labor
Then add a water pump, oil pump, timing set and tensioner, 8 quarts of oil (overfill plus one for cam splash oiling), coolant, and whatever small parts.

It's basically a $5000 job.

And it will suck to do all that and still have the root issue.

 

I might try the compression test, just for giggle. May just test two or three cylinders, and see what ya get.

Is the only code you are getting for misfires on 3? Could pull the valve cover, and check valve movement.....

 

Yes, 0303 is the only code it's setting.

It's perfectly fine at idle. Based on the freeze frame it's not setting the code until 50% throttle or 75% load.

 

Collapsed lifter, or clogged fuel injector?

 

I'm not sure how much of a PITA it is to change an injector under there (I know it was a PITA putting them in on the dakota 408 on the engine stand), but after a $42 coil, I might just throw a $50 injector and set of O-rings at it for grins and giggles.

Because those 2 options are exactly where I'm hung at. Either the lifter is collapsing under high cylinder pressure, or an injector is hanging open at high pulse width.

 

probably a flat lobe on cam, very common on the 5.7 hemi. Take the valve cover off and measure valve travel.