super20g

I have an 06 WK 4.7 w/ 60K miles that started misfiring under load and losing almost all power. I limped it home.

The ECU had 'P0300 - Multiple Cylinder Misfire' stored in memory.

I pulled the negative battery cable to clear the code and replaced all spark plugs.

The misfire under load was still there, not plugs. Idle sounded normal though. The CEL flashed while it was misfiring, key dance got 'P0307 - Cylinder 7 Misfire'.

I erased the code and swapped cylinder 5 and 7's coils. Got code P0307 again, not the coil. Cylinder 7 read 120 PSI compression.

Installed a new injector in cylinder 7 along with running a 1/2 can of Seafoam through the throttle body and another can in the gas tank.

It was still missing a bit but then smoothed out after a few seconds of WOT and appeared normal for 10 minutes, then it started missing again going up a low grade at low rpm in high gear and threw code 'P0300 - Multiple Cylinder Misfire' again.

I ran the other 1/2 can of Seafoam through the throttle body and it hasn't thrown a code again after a light drive around the block, but it seemed like there was still a slight underlying stutter at times.

Edit: Drove it to work this morning, 25 minute commute, and it didn't throw a code, but it did seem like there was still a little bit of a stutter at times.

This issue does follow a leaky driverside exhaust manifold that was replaced a month ago, but I am not sure if it is relational or coincidence.

fishbone

I have seen this before when there is an interruption in the fuel supply and also when there are cpu issues. The multiple misfire code would indicate such. Likely it is not a coil and you have replaced all the plugs and your compression is good, I would look at fuel pressure, pump voltage, blockage in the line at fuel filter. Certainly 1 bad plug, coil or cylinder would not cause you to "limp" home, it would be a rough ride especially up hills but I suspect there is an issue with fuel supply cpu as a last resort. Your mileage does not dictate an internal engine failure (although it is possible) and these are great engines. A voltage issue is also possible interrupting the flow of proper voltage from coil to coil or from injector to injector this would also cause the cpu to throw the multi misfire code. Voltage issues are often traced back to the cpu.

super20g

Update: I ran a can of Mopar combustion chamber cleaner through the throttle body and another can distributed through the cylinders, took it out for an aggressive drive, changed the oil, and now it seems to be much smoother and hasn't thrown another code after a few test drives.

fishbone

I am not a big fan of any additive...period! You likely have a real issue somewhere and it needs to be found and will probably not be cured by a can of anything. You mentioned that the exhaust manifold was replaced, I have not ever seen a misfire code thrown due to a leaky manifold gasket. Usually you will get a P0171 or a P1195 when there is a gross exhaust manifold leak. Do you have a code scanner? It is best to use a code scanner. If not go to Advance or Autozone and ask them to pull the codes and see if there are any pending or stored codes that maybe associated with this issue.

super20g

Yes, the rear two studs on the exhaust manifold sheared off causing an exhaust leak and subsequent warping of the manifold itself before the problem was noticed and remedied.

Since the exhaust leak occurred just prior to this multiple random misfire issue, I figure it 'may' be possible that it was running rich during that exhaust leak (noticed decreased gas mileage) and that may have added additional carbon deposits in the combustion chamber/head that caused the valves not to seat properly and could have been causing the misfires? Still odd that it seems to have just started all of a sudden according to my wife who is the daily driver.

It's a little bit of a stretch, but the Seafoam throttle body treatment and Seafoam/Techron fuel treatments did get the motor running smoother and then the Mopar Combustion Chamber Cleaner treatment to the throttle body and directly to the combustion chambers has so far fully resolved any hesitation/misfires and subsequent CEL's after 4 normal commutes/~30 miles...