Cylinder 5 Misfire (Help Please)

[asphaltforeman]

2021 Ram 1500 Laramie
115,000 miles. Oil change at every interval, done at dealer.
One owner, I put these 115,000 miles on it for work. It's been taken care of.

P0305 Cylinder 5 Misfire that won't go away. I replaced the spark plugs in all 8 cylinders, as I was due.
Replaced the coil pack for Cylinder 5. Still a low idle misfire. Truck runs great when above idle rpms.
Any suggestions before I put it in the shop? Injector? ECM or PCM?
This only happens after the truck warms up.

 

[KMach]

To confirm, did you replace all 16 spark plugs? Oil done at every interval meaning? Every 10,000 miles? Does the engine sound like a sewing machine with ticking? Assuming it is a all highway truck, but engine hours would be helpful. Injectors are prone to failure and excessive carbon build up. First I would perform the “pull push pull” test on the connectors. Then, swap 5 and 3 to see if problem follows. Providing wiring checks out for coil and injectors and problem doesn’t move, I’m leaning toward a bad lifter and worn cam. Pull the oil control valve under the intake and inspect for metal.

 

[asphaltforeman]

To confirm, did you replace all 16 spark plugs? Oil done at every interval meaning? Every 10,000 miles? Does the engine sound like a sewing machine with ticking? Assuming it is a all highway truck, but engine hours would be helpful. Injectors are prone to failure, I would swap 5 and 3 to see if problem follows. Providing wiring checks out for coil and injectors and problem doesn’t move, I’m leaning toward a bad lifter and worn cam. Pull the oil control valve under the intake and inspect for metal.

Yes, replaced all 16 spark plugs. Oil is changed at dealer at every 8,500 give or take. Gets close to 10,000 some times depending on how busy I am. No mechanical tick, but I have replaced the exhaust manifolds 4 times. In between cracked manifolds, when it doesn't sound like a pulp wood truck I can't hear a mechanical tick. Like I said, I've taken real good care of it. I'd be shocked if it were lifters or a worn cam, but I've been wrong before in my life.

 

[KMach]

Perform the pull push pull test then swap injectors. You may get lucky and see that they are very dirty and the problem follows. If not, I have seen a few broken valve springs and sometimes you can see on a visual inspection. If all that checks out, I’d suspect deeper. I have a huge fleet of these, typically the first time it loses a cam and lifter is in the 90-120k range.

 

[asphaltforeman]

Perform the pull push pull test then swap injectors. You may get lucky and see that they are very dirty and the problem follows. If not, I have seen a few broken valve springs and sometimes you can see on a visual inspection. If all that checks out, I’d suspect deeper. I have a huge fleet of these, typically the first time it loses a cam and lifter is in the 90-120k range.

I've never heard of this test. Do you mind explaining?

 

[KMach]

Just as it sounds. Be sure all coil and injector connectors are properly seated by pulling, pushing then pulling again. Likely not the cause but something to do.

 

[asphaltforeman]

Just as it sounds. Be sure all coil and injector connectors are properly seated by pulling, pushing then pulling again. Likely not the cause but something to do.

Ah, yes. Thanks for that. I went back and did all that after I changed spark plugs. All the connections seem to be good.

 

[asphaltforeman]

Sorry, for the delay. I’ve been swamped at work. I appreciate all the help from you guys. Just to recap, I ended up changing the plugs (16) and the coil pack for #5 cylinder. As a last resort I changed the injector for #5 and the misfire has been non-existent since. Like I said, it was due for plugs anyways since I am at 115,000 miles. That was being completed regardless of the misfire. I have a spare coil pack that is apparently good and a truck without a misfire. I plan on changing all the injectors at some point, but at $60 a pop I will take my time purchasing then change all at one time. Once again, appreciate all the tips for you guys.


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