I have a 94 Explorer with 248K miles and at the end of my rope.
After warm up only, it misses and backfires around and above 4000 rpm. I have replaced the following (in this order) in an attempt to correct it and am now broke. I lost the "let's replace this sensor game".
plugs (3 different sets, autolite / bosch / motorcraft) wires (2 sets, just to make sure) fuel filter crankshaft position sensor throttle position sensor fuel pressure regulator both oxygen sensors fuel injectors (fuel pressure reads 33lbs at idle and 39 under load) EGR valve & tube (it broke) MAF (Ford dealer = lying sack o' crap) coil pack Ignition control computer (up by the battery)
It idles fine and runs fine up to around 4000 rpm. If you start it up cold and just run the crap out of it, it doesn't pop or backfire at all until it has warmed up. It you just drive with a steady throttle at above 4000 it just bucks and pops and sputters. Same while sitting in park.
There are NO error codes in the computer, it thinks everything is dandy. The Ford dealer put it on their computer and it also said that everything was dandy (while popping and backfiring at the same time).
I have the fuel pressure gauge and vacuum gauge duct taped to the windshield and no hood on the thing. I am out of ideas.