'94 misfire with MAF, no misfire w/o MAF

[Slysdexia]

I've been fighting a misfire in my '94 Ranger that is as maddening as anything. It's a Std cab, styleside with a 4.0 Cologne and a 5 speed. No check engine light when everything is hooked up.

The truck runs fine, idles a little less than smooth (can hear an inconsistent misfire if you listen to the exhaust at idle), and has good power, as long as you're very, very smooth on the throttle below 2k RPM. If you load it up below 2,000 RPM, it bucks like it's running on 3 cylinders, and not always the same 3, a rather unsettling and frustrating behavior. It also stutters of you jab the throttle, just falls on it's face like there's a momentary rev limit at idle under WOT. Backing out of the driveways, it'll misfire consistently, or sounds like it (though doesn't feel like it).

The plugs are clean looking, though I think they're Bosch, The wires look newish (I've had the truck since last august, so I'm going to be vague ion it's history), coil pack looks to be OE. I first cleaned the MAF, having been told on another forum that apparently the only thing on earth that could possibly be wrong is the MAF being dirty (some frustration there...), when it did squat, I bought a reman MAF and with it plugged in nothing had changed, so I returned it. Unhooking the Fuel Pressure Regulator's vacuum line did absolutely nothing.

I'm at a loss, and want this misfire dealt with before it causes me trouble.

 

[Roadrunner777]

My first thought was fuel pressure/volume. If I were feeling lucky, I might just throw on a new fuel filter. If I felt methodical, I might put a pressure gauge on the rail and if that was good, measure volume. I'm away from my books right now, but I know the pressure spec is on the forum here somewhere, volume should be about 1 quart in 30 seconds.

Edit: Plugged up cat converter might do this too, or anything that would impede airflow through engine. Saw one like this ended up finding a rag sucked up the intake to the air filter.

 

[Slysdexia]

My first thought was fuel pressure/volume. If I were feeling lucky, I might just throw on a new fuel filter. If I felt methodical, I might put a pressure gauge on the rail and if that was good, measure volume. I'm away from my books right now, but I know the pressure spec is on the forum here somewhere, volume should be about 1 quart in 30 seconds.

Edit: Plugged up cat converter might do this too, or anything that would impede airflow through engine. Saw one like this ended up finding a rag sucked up the intake to the air filter.

Well, it's got a new cat (dealer had to to make it pass) and a new fuel filter (I looked and it was the factory piece, so immediately bought a new one). I'm startinhg to suspect the FPR, or possibly the pump.

 

[skderen]

Just did my FPR. Funny thing with mine was when I tested the old one, it was within spec as far as fuel pressure went, although on the low end (30 psi). But when I removed it and shook it, it made this terrible rattling noise - I figure the spring inside must have been going out. Needless to say, got a new one.

It's like driving a new X now - have power again, engine runs super smooth, all that jazz.
Good luck.