On a 1999 4.0 I have a pressure gauge hooked to the fuel rail.
When the switch is turned on (fuel pump runs a couple of seconds) the pressure goes up to 65lbs and quickly drops to 8lbs.
Is this normal or are the injectors bad ??????

 

No, most likely cause is the Check Valve in the fuel pump OR fuel filter

1999 should have a 3 Hose fuel filter
One comes from the pump, the other goes to the engine
The 3rd is the Return line that has a pressure valve that sends fuel pressure over 65 psi back to the gas tank.

You can pull out all the spark plugs and crank the COLD engine, you will get a big cloud of gasoline from a cylinder with leaky injector

 

OK could this leaky injector cause it to miss fire?
Presuming not enough fuel????
Should the fuel pump or filter be change before changing the injectors????

 

Yes, a faulty injector will cause a misfire specific to that one cylinder.
But so will faulty spark or low compression.

Might be easier if you describe the running problem with your 1999 4.0l Ranger.


But there are some general tests you can do.
All fuel injection computers have a built in routine called "Clear Flooded Engine"
If shuts off fuel injectors but leaves Spark working.
You turn the key on
Press gas pedal down to the floor and hold it down all the way

With TPS(throttle position sensor) at WOT(wide open throttle, gas pedal to the floor), and engine RPMs at 0 the computer will start "Clear Flooded Engine" routine.
So it will not open fuel injectors until gas pedal comes off WOT

In your case since fuel pressure is dropping with key off, I would Prime the system 3 times and then do the test.
So turn the key on and off 3 times, fuel pump will prime the system 3 times.
Then press gas pedal down to the floor and hold it down
Now crank engine to start it, it should NOT start, it should NOT fire at all, spark only/no gasoline.
If it starts or fires then you DO have a leaking injector.

OR..............you need to do Throttle Cable mod, because throttle cable has stretched so no WOT
Google: Ranger Throttle cable mod
Takes about 4 minutes to do

And you can use this test to find the leaking injector.
Disable spark, unplug the 4 wire connector on Coil Pack
Repeat the test, do the Priming 3 times as well.
Now pull out the spark plugs, they all should be DRY, except the one with the leaking injector, it will have a wet tip.


You change a fuel filter every 5 years or so, so if you don't know when it was last changed then spend the $10-$15 for a new one, it should come with a tool to release the fuel line fittings.

 

Ok, I just did the clear flooded engine routine, didn't help......
When this thing is started, cold or hot, it idles rough, and when put into gear (automatic) it appears to be worse, maybe because a load on the engine. If taking off slow it chugs along but if the pedal is pushed down pretty hard it seems to run somewhat better. When on the highway it misses and chugs at cruising but there again, when pedal is applied hard it seems to run up good, or maybe just can't feel the miss when accelerating. If the pedal is applied ever so slightly, it really gets bad, feels like the thing is fixing to come apart.There seems to be pretty good power (considering the miss) because it hauled a good sized load of wood for 40 miles, but it chuged at all the mentioned pedal applications.

 

On another note, yesterday when the AC was turned on for the first time this year, the cold air only came out on the defrost part (windshield), everything was tried and the only place air would come out was the windshield. This stuff is vacuum controlled,,RIGHT??? Maybe the is a leak some where !!!!!!!I'm going to check that out now...

 

Found a broken vacuum line that controls the air damper. Fixed that, but that didn't change the way it runs...8-(

 

"Ok, I just did the clear flooded engine routine, didn't help......"

Its a TEST, not meant to fix anything, so did the engine start or fire with gas pedal to the floor?

Is the CEL(check engine light) on?

And does CEL work, i.e. does it light up when key is turned on, or is bulb burned out?

If no CEL with key on then you will need to read the codes, most auto parts stores will do that for free, have pen and paper to WRITE THEM DOWN, "I think it was.........." is worse than no codes at all

A misfire, which it reads like, will set a code and turn on CEL, i.e. P0304, misfire cylinder #4.
A leaky injector will cause Rich mix on that bank of the engine will also set a code.

Yes, you will feel a misfire more in gear, any load will feel worse.

Some common issues are dirty MAF sensor, easy to clean.
Worn spark plugs, need to be cleaned and regapped, or replaced
Spark plug wires, usually last 15 years or so.

 

No it did not start WOT
The CEL was burnt out, now replaced, that was a job!!!!
Number 1-2-3 injectors were ohm checked, all the same, the same three plugs were checked and all deliver 12 volts with key on not running.
Going to Auto Zone to get codes checked.
Will let you know.

 

P0303
P1131
P0304

 

If it didn't fire or start doing Clear Flooded engine test then injectors are not leaking, for sure.

For OBD codes
P0xxx means generic not model specific
P1xxx means model specific, so Ford and maybe Ranger

P0303 - misfire #3 cylinder
P0304 - misfire #4 cylinder

P1131 - means Passenger side of engine O2 sensor is showing Lean and not switching when computer adds more fuel to that bank, Bank 1

Lets do misfires first since they can cause Lean codes.

There are only 3 coils in the Coil Pack
#3 and #4 spark plugs share one coil in the coil pack, so both spark/fire at the same time.
2 and 6 share another and 1 and 5 share the 3rd

You have a OHM meter so I would test the coil pack.
Short Video here on testing it: www.youtube.com/watch?v=c1zhgsnyZWw
Not hard to do.

3 and 4 don't have a whole lot in common, they are on opposite sides of the engine, so coil pack would be my bet, maybe spark plug wires, because they do share wires as well.
The spark plugs sharing the same coil are wired in series, so if one wire is bad it can effect other cylinder firing.

O2 sensors "see" Oxygen in the exhaust, not gasoline/fuel, so when a cylinder misfires no Oxygen is burned, used up, so it gets dumped into the exhaust and O2 sees that as Lean exhaust, too little Oxygen is Rich.

So if you can cure your Misfires the P1131 code may not come back, but............
I would have expected P0171-bank 1 lean, instead of P1131, that almost makes me suspect O2 sensor has over 120k miles on it and is due for a change.
But cross that bridge after fixing the Misfires

 

OK-------I put new injectors in, which was what a local mechanic said it probably was the reason for the miss, giving I've done all the electrical checks, coil pack included, compression checked good on all 6 cylinders, there are no vacuum leaks, no broken wires no NOTHING----I'm REALLY GETTING UPSET WITH THIS THING !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Misfire is one of three things on a gasoline engine
spark
fuel
compression

So testing was incomplete on one of them