Ok so I have a 94 ford ranger 4.0 4x4. When I bought it it had a rough idle and a miss. So I get it home and I change the spark plugs, spark plug wires, coil pack, maf sensor, fuel filter, and air filter. It smoothed it out some but now it will run till 3k rpm then it acts like it's missing. It straightens out a little around 4k rpm. Idk why it is doing this lol need help thank you

 

Welcome to the forum

Alot of stuff to change at one time

Double check coil pack firing order.
3 4
2 6
1 5
Front

The 5 6 4 side often gets mis-wired, also follow each wire to its cylinder, 4 and 5, 5 and 6 can get reversed

takes a few warm ups for computer to learn new MAF sensor.

I need to run a can of Seafoam in the gas tank once a year on my '94 4.0l, starts to idle rough after a year or so, the injector cleaner smooths it back out.

You pretty much have to use Motorcraft or Autolite spark plugs in the 4.0l, it "eats" other brands.
And use Regular copper or DOUBLE platinum, never single platinum in Fords with a coil pack, waste of money

What did the old spark plug tips tell you?
Blackish
white
brown


If its a vibration you feel at around 3,000rpm then could be failing fan clutch, had one do that to me, check it to make sure it doesn't wobble at all, after engine warms up.

Does CEL(check engine light) work?
It should come on when key is turned on, then go off once engine starts

 

Hey, thanks RonD. The ignition pattern is right I got it out of the Haynes manual, same one you suggested. I'm going to try the sea foam and hope it works, the spark plug tips were scorched black. Also at 3k rpm it's like it boggs into a miss. Definitely a misfire thank you

 

Black spark plugs is Rich running
And you will need to change the two O2 sensors, because they are ruined by Rich running, pull one and see if it is black as well

On the lower intake at the front passenger side by alternator is the Fuel Pressure Regulator(FPR)
It has the Return Fuel line attached AND a vacuum hose
That Vacuum hose runs under the coil pack around the back of the upper intake and to the vacuum manifold, drivers side upper intake.

If the FPR should leak, raw gasoline will be sucked into the engine via that vacuum hose.
Black spark plugs

If vacuum hose has no signs of gasoline inside it then FPR is OK, if gasoline is found replace FPR.

Next is the fuel injectors
Easy test
All fuel injection computers have a "Clear Flooded Engine" routine
This routine leaves spark on, but shuts off fuel injectors while engine is cranking

Turn key on
Press gas pedal down to the floor, and hold it down all the way
(at 0 RPMs, throttle position sensor at WOT-wide open, computer starts "Clear Flooded Engine")
Crank engine over

It should NOT start, it should not even fire, there should be no fuel only spark

If it starts or fires then you have a leaking injector, black spark plugs
You can tell which injector using this test as well

And just an FYI, I use the "Clear Flooded Engine" routine every time I cold start my 400k 4.0l engine now, lol, high miles and I want to circulate some oil before it starts
Crank engine while I count to 5 and then I release gas pedal and it starts, no lifter ticks or other noises.
"Clear Flooded Engine" is great to pre-lube high mile engines

Not that I am suggesting any thing nefarious, but "knowledge is power", so........
Buying a used vehicle, try the "Clear Flooded Engine" routine.
Seller will say "hey, it has ALWAYS started first time?!!??"

 

Hey RonD, I checked the FPR vacuum hose but it didn't smell like gas. I ran sea foam through the gas, oil, and throttle body, then changed the oil. Still nothing. I also sprayed brake fluid on all the vacuum hoses I could find and nothing. Can't find the bad one. Also, I can't get it to go in clear flooded engine mode. I tried holding the gas pedal to then tried turning it on and it started right up

 

Google: Ranger throttle cable mod

Your throttle cable has stretched so you can no longer get WOT(wide open throttle) at the engine, so you can't get TPS(throttle position sensor) to full voltage, above 4.5volts, so computer never sets Clear Flooded Engine mode

To see if thats the problem, have someone press down gas pedal all the way, or put a stick on it and against the seat to hold it down all the way
Then go to the engine end and see if you can open the throttle more manually, if so then do the throttle cable mod, it is simple and easy, couple of Zap straps on the cab end of the cable

If thats not the issue then TPS could be bad
You can check it with a volt meter
Set meter to DC Volts
Use a sewing pin/needle to pierce the Center wire on TPS
Turn on the key
Ground meter and put red probe on the Pin
Should read under 1volt, .69-.99 is spec
Manually open throttle while watching voltage
Should go up steadily, no jumping or dropping
At WOT is should read above 4.5volts