'91 2.3L EFI won't accelerate.
 

My son got a '91 Ranger with a 2.3L EFI and a five speed. When he got it it wasn't roadworthy, it needed rear springs, grille, steering shaft, brakes, brake lines, front shocks, one day at pick n pull, a truck load of parts and a few days and it's roadworthy...
We have a problem...when we try to accelerate the truck will sputter and sometimes backfire. The engine runs fine to half throttle position then it acts like it's starving for fuel. If it's parked and you push the throttle about half way it will run to the rev limiter but if you push it all the way it'll sputter back down to around three thousand. It's also hard starting when cold, when it's warm it starts fine.
Checked the plugs (it has two sets ) they are fine, it runs like a dream at idle and if you rev it slowly.
Added fuel, replaced the fuel filter, checked timing, alternator isn't working (taking it in to get checked tomorrow) but the voltage is above 12v.
The fuel pump runs for five seconds and cuts out when you turn on the key, sounds OK, runs all the time when the engine's running. I haven't been able to check the fuel pressure yet (don't have gauge) but I opened the valve with a small screw driver while it was running, it doesn't seem to have allot of pressure and the engine sputters when I open the valve.

This is a fascinating engine! Like I said it has two sets of plugs and the ignition cuts out till the engine comes back to idle, seems to be ahead of it's time. I would think it should have more than a hundred hp . This truck has tall gears, it'll do a hundred km/hr in second gear easy and does about 1600rpm at 100km/hr in high gear, it's gonna need everthing that engine can produce to maintain the speed limit .

If anybody has any ideas I would really appreciate your feedback. Thanks.