I recently purchased a 15 1500 Ram SLT 4x4.
check engine light came on and discovered cylinder No 3 was misfiring. Changed the plugs as they were original ones. Was fine for 400 miles then check engine light came back on. Again computer showed misfire in No 3. Put new coil pack on..no change. Compression test was good as were fuel injectors.....weird thing is computer only shows misfire over 3000 rpms.
My mechanic said he doesn't know what else to check and said take it to a dealer but I know they're high as hell!
Any ideas?? Any ideas??
Thanks.

 

What plugs did you install?

How did you determine the injectors/coils were ok?

 

Bosch iridium.
Switched coil packs to no avail and then put brand new coil pack, no change.
Removed injectors, cleaned and swapped to different cylinders. Again no change.
Computer only shows misfire over 3000 rpms.
I guess lifters would be next to check or valve springs? 🤷🏼‍♂️

 

Bosch iridium. Replaced all 16 plugs.
switched coil packs to see if misfire followed the coil pack, it did not. Put a brand new coil pack on cylinder 3 anyway, no change.
Did compression test and it was good.
Switched fuel injectors, again to see if misfire followed it. It did not. Removed injectors and cleaned. Same outcome.
Cylinder 3 misfires over 3000 rpm.
Maybe check lifters and or valve springs next? 🤷🏼‍♂️

 

The iridium plugs may be at least a part of your problem...... I believe the factory preference for at least 8 of them, is coppers...... On the older trucks, the rare-earth plugs tend to create mysterious performance issues, like misfires.....

 

Thought I read somewhere that iridium was oem recommended plugs.
Guess I'll have to research it some.

 

That's possible, I just don't know..... Though, I have heard rumors that its half and half... the plugs that are fun to get to, are iridium/platinum, the others are copper.... But, I think that was for the 4.7... on yours, aren't the plugs right next to each other??

 

Yes, plugs are side by side 2 per cylinder.
And I just read 14 and up came with iridium plugs.
On a side note, check engine light was off yesterday and this morning.... Then coming home this evening I got on it a little to see if it was truly sorted out and surprise.....cel popped back on...

 

Might wanna do a compression test on that side, and see what the numbers look like.

 

We did one on cylinder 3 and it was 180 and held.