Yesterday my truck start bucking i plug in the obd2 code reader it says it was the cyl 5 in problems sometime it runs good sometime its really bad i changed my spark plugs my wires and now thincking about changing the coil pack but dont know if its the right thing to do im new to the ranger world and dont know if its a problem on the 3.0L thx for your help and advise!

Its a 03

What brand plugs, wires, coilpack ? How many miles ?

Mine just started doing the same thing and I just got it fixed. It was giving me P0306 and P0316 codes constantly. Idling really rough to near stalling. Ended up being a faulty fuel injector causing a lean condition, which in turn, burned the head and wrecked the intake valve and seat. Got the head resurfaced, got the valve and seat replaced, and got all of my injectors sent out for rebuilding. Engine was under warranty, so I paid $480 for diagnostics and the other 5 injectors.

However, this may not be your case. I've heard people spending thousands to get this exact thing go away and it being something as simple as changing the fuel filter or a spark plug. I'd start cheap and simple (spark plug, wires and coil pack) and then work my way to a compression test if it's not working. Unfortunately, the #5 fuel injector is under the intake manifold and basically impossible to check without taking all of that out. Luckily, it is isolated to 1 cylinder so you have specific items to look for. Good luck man!

There's a TSB for 04-06 rangers for this problem as well, not sure about it affecting 03's, but it's a start.

TSB 05-26-3

12/31/05
MIL ON WITH VARIOUS MISFIRE RELATED DTC'S
P0300-P0306 AND P0316 - 3.0L-2V VULCAN ENGINE
FORD:
2004-2006 Ranger
ISSUE
Some 2004-2006 Rangers 3.0L-2V "Vulcan" vehicles may exhibit:

^ Malfunction indicator lamp (MIL) on with diagnostic trouble codes (DTCs) P0300-P0306 and P0316

^ Rough running at various RPM

^ Rough idle

^ Misfire

ACTION
This may be due to an engine exhaust valve seat recession causing a loss of compression. Refer to the following Service Procedure to diagnose exhaust valve seat recession.

SERVICE PROCEDURE

1. Perform a power balance test to clarify if a cylinder is misfiring. Identify and keep record of any cylinder that has a concern.

2. Perform a manual compression test with the spark plugs removed to locate any cylinder that may have low compression. Refer to the appropriate Workshop Manual, Engine System, General Information, 303-00.

3. If no low compression is found per shop manual instructions, proceed with normal misfire diagnostics per the Powertrain Controls/Emissions Diagnosis (PC/ED) manual for the appropriate model year.

4. If low compression is found and it is a cylinder that had a misfire on power balance, perform a leakdown test to determine the source of leakage that may be causing the low compression. Refer to the appropriate Workshop Manual, Engine System, General Information, 303-00.

5. If low compression is found in a cylinder that did not have a misfire detected then proceed with normal base engine diagnostics per the Workshop Manual, Engine System, General Information, 303-00.

6. If the exhaust valve is identified as the source, replace both cylinder heads with the newly released service cylinder heads. Refer to the appropriate Workshop Manual, Section 301-01A.