94 4.0 ranger issues need input

[built2drags10]

I have a 94 2wd 4.0 ranger. 188k miles

started losing power at lower rpm's and idling a little rough.
now it will barely stay running at idle. Its running extremely rich and throwing no codes.

I changed the plugs,fuel filter, has a new maf , new tps , new coil and a new fuel pressure regulator.
when I changed the plugs all 6 plugs were uniform which makes me believe the problem is on all 6 cylinders.

when I unplug the maf the idle improves a little, but not much. thats actually the only way it will idle by itself is with the maf unplugged. still runs really rough and is puffing black smoke.

any ideas ?

 

[CraigK]

Try unplugging your oxygen sensor.

CraigK

 

[built2drags10]

I already tried unplugging the o2's. no change.

would a coolant temp sensor or a cam sensor cause something like this ?

 

[tobyduck]

Check your IAC valve, if it is dirty on the inside, most of the time it doesn't move freely all the way.

 

[built2drags10]

Tried that too.. I poured some of the gas out of the filter I put on a few days ago and it looked nasty. Im going to put another fuel filter on in the morning and take a look at the gas. The truck had been sitting up for about 2 years with 1/4 tank in it. I filled it up and it had been running pretty decent before it messed up. I guess I've put around 300-400 miles on it since it was sitting up. Maybe there is a problem there.

 

[sidecarhammond]

i believe I have the answer to your problem ....

OK, automatic transmission, correct? I had a 1988 Ranger w/ the same problem. Tried everything .... you need to replace the vacuum modulator on the transmission. It has gone bad and is leaking vacuum, completely throws off the computer. Here's how you test: There is a vacuum line running to the transmission; should be at the top back of the engine. Find the line, disconnect and plug the vacuum to the motor. Start the truck. Take a drive around the block. The motor should smooth out and the black smoke will go away; the trans will NOT shift, though. But this is only a test.

If the motor suddenly runs fine, this is your problem. Hope this helps .....

 

[built2drags10]

Ended up being bad gas. I drained the tank and filled it back up with good gas and its now running 100 times better.