I have a 1994 Ranger 4.0
My truck just developed a bad skip driving slow or fast, hot or cold. I recently changed the plugs and wires and coil pack. In the last couple months I have changed the MAS air flow sensor, IAC, TPS, O2 sensors, and vacuum hoses.
I'm hearing it could be injectors, cam position sensor, or it may need a head job.
I don't know how to check if an injector or bad and may have to take it a shop to get the compression checked.
Advice would be greatly appreciated!

 

Welcome to the forum

You most like likely have a bad spark plug, yes new ones do break, and the 4.0l OHV engine "eats" spark plugs, Motorcraft or Autolite seem to last the longest
Best thing is to remove each one and inspect it, crack in the ceramic is most common failure
Spark plug tips should have a light brown color if they are working OK, clean and white means it probably isn't working

And as part of above:
Yes, you can test if each fuel injector is working
Cold engine
Unplug the 4 wire connector on the Coil Pack, you want No Spark
Now crank the engine a few times
Pull out each spark plug, all should have WET tips, Dry tip means that cylinder injector is not working
Look for cracks in ceramics and light brown color

Check the spark plug wiring on the Coil Pack
3 4
2 6
1 5
Front
the 5 6 4 side can get mixed up, trace each wire from cylinder to coil pack

If you have insulated gloves or pliers you can pull spark plug wires while engine is idling, and misfiring, if pulling spark plug wire doesn't effect RPMs then that spark plug is not working
Ford Waste Spark System doesn't make this 100% reliable but it can narrow it down to 2 cylinders, i.e. if you pull off #6 wire and RPMs do not drop then problem could be #6 OR #2, see coil pack wiring above
3/4, 2/6, and 1/5, pairs, share the same coil

1994 4.0l shouldn't have a Cam Sensor unless it is from Calif.

You can check injector wiring, push down on connector to make sure it is tight, but fuel injectors rarely fail enough to cause a steady misfire, when an injector gets dirty or starts to fail you get a Lean Code and intermittent misfires at lower RPMs
It is possible just way way down on the list

Steady misfire will be spark related 99% of the time

Yes, exhaust valves can get burned so that cylinder loses compression, and a compression test would tell you if that happened, and normally that would be MY first stop on a STEADY misfire, but wouldn't pay for it to be done until I checked out spark plugs, lol.

Just FYI, never use Single Platinum spark plugs on Ford's Waste Spark Systems, its a waste of money, use regular copper or Double Platinum, "single" anything will wear out the same as regular copper, so waste of money

 

Thanks Ron D! You were right. I changed all of the plugs and it's back running great! They all looked brown/tan color except one of them. The number 5 cylinder was kind of oily black. I guess that means oil getting in there from maybe the rings?
The truck does seem to run very rich. If I have the back sliding glass open and I come to a stop, I can smell heavy gas fumes through the back window. I would have thought the O2 sensors but I changed them and no help. Any suggestions?
Thank you again for you help. I have lots more questions

 

Good work

Oily spark plug is usually failing valve guide seal on the intake valve in that cylinder, if it gets too bad you can change these without pulling the head
Working PCV Valve system helps prevent some of that oil getting into the cylinder.

On the 4.0l behind the alternator on the lower intake you will find the Fuel Pressure Regulator(FPR)
FPR has the Return fuel line attached AND a vacuum hose
If FPR starts to leak a bit then gasoline is sucked into the intake via that vacuum line, causing Rich running
Check that vacuum hose for fuel or fuel smell, replace FPR if found

Exhaust manifold leaks cause Rich running
O2 sensors read Oxygen levels, not fuel, too little oxygen is Rich, too much oxygen is Lean
If there is an exhaust leak between head and O2 sensor it will SUCK IN air because of the scavenging exhaust system used
This fresh air causes O2 sensor to see too much oxygen in the exhaust, a FALSE Lean, so computer adds more fuel and engine runs Richer than it should