Hello to all, I'm new to this forum.
I've been having an intermittent issue with my 2004 V6 3.0 ranger 122K miles. Started with cylinder 5 misfire, changed sparkplugs (NGK), cables (NGK), ignition coil pack (OEM). Issue went away for a month. Returned with a cylinder 4 misfire P304 and Misfire at startup. P0316. I changed sparkplug and issue went away for a few days and has intermittenly returned. Changed Coil pack once again, cable and sparkplug for the third time on cylinder 4. No resolution. Truck started shaking at idle and when i come to a stop. Any advise? Thinking of changing the fuel injectors, not sure how big of a job it is. Any help is appreciated.I've also tried a few fuel injector cleaners with no luck. The last fuel injector cleaner i used seemed to make the issue worse.

 

Update,
I was hesitant to do fuel injectors myself but i went ahead and changed them out with **** from RockAuto. Misfire did not go away. I finally looked into doing a compression test and bought the tools to do it. I should have done this before spending $300 on injectors. Cylinder 4 was reading 85 PSI while others were at 150. I proceeded to do a wet compression test by pouring a small amount of engine oil directly into the cylinder via the spark plug hole and pressure jumped up to 130 psi. I found my problem. Worn piston rings. quoted $8.5K to change the engine with a Jasper 3yr warranty from a local shop who said they do not overhaul engines. I do not know what route I’m going to take but currently looking at a used engine swap.
Would it be worthwhile doing an overhaul on my 121K engine? Not sure why it failed so soon, since i owned it, I’ve changed oil every 6months with full synthetic (****). My father-in-law owned it before me and never had issues.

 

121k miles is a bit low, but sounds like a recessed head / exhaust valve seat issue. What did you end up doing? 2004, 2005, 2006 3.0 Vulcan motors had this issue. I hear motors go for 300k miles.

Low Pressure in Cylinders 1 + 2, error reads lean bank 2 - Ranger-Forums - The Ultimate Ford Ranger Resource

Engine - MIL ON/Misfire DTC's/Runs Rough/Misfires — 2005 Ford Ranger 2WD V6-3.0L VIN U Service Manual | Operation CHARM