Okay, so just bought this truck, so history is completely unknown. Was told by the p/o that they just replaced spark plugs and radiator when i bought it. After i had originally bought it, it had a very bad misfire from cylinder #7. Got around to looking at plugs and apparently they dropped the plug or something because there was no visible gap. Installed all new Mopar plugs from dodge misfire went away...from cylinder 7... Ran great fro about a week it seemed, but i felt the coolant temp gauge was sitting too low, so then i replaced the thermostat and added some fuel additive. Then on my way home the CEL came on, was misfiring at an idle, and after checking the codes, found a P0301 - Cylinder #1 misfire.

Checked the obvious, swapped the spark plugs from cylinder 1 to cylinder 3, no change, swapped injectors from 1 to 3.. no change. CEL comes on within 10 miles of driving every time on cylinder #1..

It feels like it only misses at an idle. Rough idle,, but smooths out great when the gas is applied or while you are driving. With no load, at an idle it misses like an SOB.

Finally got around to checking compression, and cylinder #1 was at 110 dry..
Checked #3 and was at 160 dry.. Didnt have a whole lot of time to look into it as it was getting late, but im assuming i have a burnt valve..

Valves a common issue with the 5.9's? Or am i completely chasing my tail? I know i need to do a leak down test, as well as test the other cylinders wet and dry, but for now im just trying to find as much information as possible and what first things i should look at.

Should also add, i get a whole whopping 9.6 MPG according to the display. About 11-12 on the freeway..

Thanks in advance for any and all help

 

Might be a lean-burn miss..... Need to verify fuel pressure. Also need to check your plenum, see if it's blown. (see the stickied thread at the top of this forum.) Have any oil consumption problems? Might also wanna check plug wire routing. There is a TSB on that, you can find it in the FAQ/DIY section.

Might try feeding the engine some seafoam via the brake booster line. See if you don't just have a dirty valve.

 

looks like a physical problem with #1. any weird noises? how many miles? swapping the injector and plug with a known good cylinder pretty much eliminated an easy fix... same with the compression test showing 50# less pressure. my next search would be the rockers for #1 or even stick a camera in the plug hole to look for damage. i'm thinking valvetrain, bad valve, rocker, spring. did you check for blowby?

 

Been fighting cyl1 misfire for 18 months. Been off/on diagnosing b/c it would go away on it's own. CEL came on at startup, idle, just as you said.

Long story short...b/c I ruled out alot of other contributers to the CEL as there is like 7 things.

Did comp and leak down test yesterday. Cracked head.

So do proper dry and wet compression test, Vacuum gauge test, and leak down test.

 

Did a seafoam treatment on it on Saturday. Seemed to help a lot but it is still there a bit. I'm 90% sure it's a valve issue. But even then, sometimes is runs great with no stumble at all, sometimes is shakes the whole truck. But, no CEL for 3 Days and even just passed an emission test this morning.