hello,
Im working on a 1990 f150 with a 4.9 i 6 for a friend and cant seem to figure it out...
the problem is that its running lean has a lack of power misses stumbles and generally runs bad... its really bad when cold (when it needs extra fuel) once it warms up it runs better but not good on the highway it runs good but still shows lean on the scanner most of the time and if it idles at a light or in traffic it sometimes starts running rough again but sometimes rins and idles fine (o2 still reads lean .00 to .06 volts most of the time but ocasionally jumps up to .88-.96v)... the mil isnt on but codes i get are lean and no egr flow detected im pretty sure the lack of egr is a bad solenoid...vacuum is 15-20 hg when it runs smooth and drops when it runs rough to 10 or less sometimes hitting 0...
He has installed new: bmap, tps, dist cap, rotor, wires, and plugs, fuel filter, egr valve, egr position sensor, iac head gasket vacuum lines and intake gaskets... fuel pressure is 55lbs at idle and drops slightly to 50 lbs when reved for a seccond or two then goes back to 55... the only things I think it could be are bad pcm a valve intermittenly not sealing or an injection problem... anyone know a good way to test the flow of the injectors or test the pcm? i did a compression and leak down test both came back good and there is no vacuum leaks i can find..
any and all help is appreciated sorry to be so long winded just want all the info i can give to help you folks help me...thanks

 

Replaced the injectors and bingo truck runs great!!!

 

The codes should give some indication as to what part(s) are malfunctioning.