If possible do a compression check.
Remove all 6 spark plugs before the test
Write down results
3.0l has 9.3:1 compression ratio, so between sea level and 2,000ft elevation you would expect 165+ psi in each cylinder
#5 probably has low compression so air/fuel mix can't ignite until compression gets higher which comes at higher RPMs.
Just to take faulty coil pack off the table swap #1 and #5 wires on the coil pack, move #1 spark plug wire to where #5 is now and #5 to where #1 was.
They are right next to each other, and use the same coil, Ford uses a Waste Spark system; because of engine balancing #1 and #5 are at Top Dead Center(TDC) at the same time, one on compression stroke the other on exhaust stroke, Ford's system sparks both cylinders when at TDC, so one spark is "wasted", hence the name waste spark system, but as far as spark timing #1 and #5 are exactly the same so swapping them won't effect spark timing. (or swapping 2 with 6 or 3 with 4)
In the coil pack #1 and #5 are hooked up in Series electrically, that means one spark plug will spark from center to tip, and the other from tip to center.
If one coil in the pack gets high secondary resistance one spark plug can fail to fire until resistance is overcome by current, higher RPM can do that.
After swapping the wires and clearing the codes, if you start getting P0301 then problem has moved to #1 and Coil is the problem.
In the early 2000's Rangers with 3.0ls did get a batch of sub-standard coil packs, that did cause P030x codes, there was a TSB about it.
Block test is good to test for head gasket issue but costs money, Glove Test is better and is free.
Why is a blown head gasket even an issue?
A cylinder has 150+ psi when cranking, and over 900 psi when firing, if some of that pressure escapes via a gap(breach) in the head gasket it generally encounters a coolant passage since each cylinder is surrounded by coolant passages, whole point of the cooling system is to carry cylinder heat away.
The pressure in the cylinder is in the form of air(exhaust but still air not a fluid), if this air is pushed into cooling system it displaces coolant in the head(air rises in fluid), this can cause head/engine to overheat since air doesn't absorb heat like coolant does to carry it away, air also tends to stay in higher areas which prevents coolant from circulating as well.
This extra pressure in the cooling system can get above the Rad Caps 14psi rating, so needed coolant is pushed out of rad and into overflow tank, causing more overheating.
On intake stroke of effected cylinder some coolant can be sucked in, since coolant doesn't "burn" this can foul the air/fuel mix and cause a misfire, at higher RPM the "air" pushed out of cylinder would be sucked back in instead of coolant, so no misfire.
In the above you would notice over full overflow tank, and in the beginning warmer engine temp on gauge and heater might blow cold now and then because "air" is being pumped into the heater hoses instead of warm coolant.
Block Test uses a chemical reaction to test the "air" in the radiator for traces of exhaust, there should be none unless a cylinder has a "blown" head gasket and is pumping that "air" into cooling system.
Remove rad cap
Remove overflow hose from rad and plug that port in rad, vacuum cap or short hose with bolt in it works
Put latex glove over rad cap opening and seal it with rubber band, a balloon or even a condom will also work.
Unplug the connector on the coil pack, you want a no start
Crank engine and watch the glove, it should just lay there
If glove starts to bounce you have a head gasket leak, the 150+ psi pressure on compression stroke is being pumped into cooling system making glove bounce
Remove 1 spark plug at a time and crank engine again
When glove stops bouncing, the last spark plug removed was from the leaking cylinder, reinstall it to be sure.
To test for leaking fuel injector you can use the "Clear Flooded Engine" routine found in all fuel injection computers.
Key on engine off
Press gas pedal to the floor and hold it down all the way
Crank engine to start, keep holding gas pedal to the floor
Engine should NOT start, engine should NOT even fire a little, fuel injectors are shut off
If it starts or fires then fuel is leaking in.
Clear flooded engine routine uses TPS(throttle position sensor) voltage to initiate.
Key on = computer on and TPS is getting 5 volts, with throttle closed TPS sends computer back 1 volt
When you press the gas pedal to the floor, wide open throttle(WOT), the TPS sends computer above 4.5 volts.
With 4.5 volts from TPS and engine at 0 RPMs the computer enters Clear Flooded Engine mode, and shuts off fuel injector pulses, but spark is still on.
As soon as you release the gas pedal injectors will start working, even while cranking engine.
If you had a leaky fuel injector engine would fire because fuel is leaking in even through injectors are off.
And just a heads up, bad TPS or short between TPS wires can cause a No Start because of this.
Last edited by RonD; 12-18-2015 at 12:41 PM.