I bought this 97 F 150 4x4 from I guy I work with. He gave me the truck pretty cheap. He never drove it and told me it was in need of a major tune up. He said he just kept the oil and filter changed, and replaced the air cleaner if needed. I bought the truck and checked everything. Went ahead and replaced the plugs and wires. A few of the wires were out of resistance range. Put motorcraft plugs in(.054) and checked the coilpacks. They were a little out of range to so I went ahead aand replaced them also. The truck had a bad miss to it when it was cold and stumbled a little while accelerating. Well the ignition tune up got rid of the miss when cold but it still idles a little rough and stumbles. Pcv system is working properly and EGR valve is holding vacuum. I checked the fuel pressure and it was pretty low. At idle it held around 35 lbs. and when I unhooked fuel pressure regulator it went to around 40 lbs. The truck never got above 40 lbs. even when reved up. The fuel was clean when purged at the fuel rail, but alittle dirty at the filter. I replaced filter and no change. My guess would be the fuel pump. Anyone familiar with this. This is my first Ford so I'm a newbie. The motor is a 4.6 With EI ignition. The truck has around 128,000 miles on the fuel pump. And I did try a little bottle of Lucas fuel treatment with a full tank of high octane fuel.

 

I know this is an old post but have you since changed your fuel pump? If so did it fix the problem? I'm having similar issues fuel pressure is about 30 psi and changed all the thing you did. I really don't wanna blow 100 bucks on a pump if it didnt fix it. Also my trucks not throwing any cel's