Ok guys working with a 2003 ford ranger 3.0L v6 auto 2wd with 119.xxx miles I am having a missfire in cylinder # 5 the engine idles hard, acceleration is **** sometimes i'll be driving and then it will start to run like crap and shake really bad then clear up and run fine then do it again. if i step on it while it does it, it seems to work fine until i get back to a normal running speed. loss of power when this happens as well. check engine light flashing at me under power and idle.

Truck is not smoking, or burning oil, or has any loss of coolant. Took it to someone that hooked it up to a machine they confirmed that my o2 sensors are working fine. Truck is a flexfuel (which has never had any of that in it) and the truck does NOT have an egr vavle.

i have read through the forums and have found some great info and based on what i have read here and another site in the past week this is what i have done.

Replaced:
Coil Pack
Plugs(104 autolites)
Plug Wires (duralast)
Alternator (NEW no refab)
Serpentine Belt
Air Filter
Fuel Filter
injector # 5 (new)

(All of this was done within the last 2 weeks) inc. Compression Test
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Compression Test:
cylinder # 1= 140psi
cylinder # 2= 139.5psi
cylinder # 3= 139.5psi
cylinder # 4= 121.5psi
cylinder # 5= 120-119.5psi
cylinder # 6= 140psi

I attached photo of plugs from cylinder # 1&5 they do not smell like gas or oil.

what do you guys think?

 

Average compression is 140, 10% of that is 14psi, so a cylinder under 126psi(140-14 = 126) would be suspect.

Since #4 is low as well I would do a Leak down test on #5 and listen if air is leaking into #4, so blown head gasket between cylinders, not common but does happen.

Overall your numbers are fairly low for a 3.0l with 9.3:1 ratio
I would expect 165psi average.
My 4.0l with 9.0:1 still has 155-160psi with 350k.
The problem will lower numbers, under 150psi, is that the 10% rule of thumb doesn't seem so bad, the 140 to 120 you got, with higher numbers the gap gets bigger so you see that there is an issue right off.

Compression test needs to be done will all spark plugs removed to get good crank speed.
Cold engine is fine
Compression gauge may just be off as well.