I apologize for the long winded post, I just want to give an accurate dipiction to allow for clarity of the situation.

I acquired a 95 F150 4.9L XL from a lady who kept her husbands truck after he passed. The truck has, "supposedly" been run occasionally over approximately a 10 yr period. I am an amateur mechanic and I'm only doing the work myself because I can't afford to have it looked at, and I also think the experience I'm gaining is invaluable.

I am currently experiencing a lot of difficulty starting the truck (3 - 5 tries), which only works if I finagle the gas pedal. Once it catches it has an extremely rough idle and usually dies once I am able to get out of the truck and walk to the engine bay, which has made it very hard to get any KOER readings (Unless the code reader is attached and running, in which case it runs "well enough"). At one point it ran well enough to drive around my neighborhood a few times, ran like **** and shifted hard into 2nd (no noise, but you could feel it). The codes I got are for an insufficient EVP (replaced the solenoid after the code), 172 Ox lean, and 538 Insufficient Throttle Response (I did mash the petal during testing).

I got a fuel pressure tester today and it only goes up to about 28 PSI (KOEO, KOER).

Pertaining to the fuel system I have replaced the rear fuel pump assembly and tank (Spectra)(midship tank is still original, not functioning), the FPR (GP Sorensen), the fuel filter (twice, now motorcraft), the fuel pump & ECM Relay (Standard).

Ignition Components Replaced - Spark Plugs, Spark Plug Wires, Distributor cap and Rotor (Duralast), ICM (Delphi), Ignition Coil (Arts/Wells)

Emissions - (Vac Reservoir intact), Vac Lines (Silicon, Amazon), EGR (Duralast), EVP (Duralast), EVR (Arts/Wells),PCV Valve (Duralast), O2 Sensor

Intake/Throttle - Air Filters, Map Sensor (Duralast), ACT (Duralast), TPS (Duralast), TBI Gasket, (Cleaned IAC)

Etc. - Coolant Temp. Sensor (Duralast), Battery (Duralast),

 

The 4.9, 300, needs minimum of 40psi of fuel pressure to run, and that's a maybe. Ideally it needs to be between 45-50 running.

I would start by rechecking the fuel pressure and be sure the gauge isn't screwed up.

Edit: I hope you kept ALL the original Motorcraft parts. I've got new over-the-counter parts that are JUNK. Hell, most of the ignition components I have are 22-25 years old and are better quality than so-called MSD quality components.
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Fuel pressure at the rail needs to be 50 - 60 running and if I remember correctly closer to the 60 mark is normal on the 4.9l, the v8 engines run 40 - 45.

 

50-60 would be static reading

Running would be 45-55.

V8 run 30-32 running
40-45 psi static.

 

Timbersteel,

I did that reading last night and I left the gauge attached to check for a slow leak. Will do another test today, the fuel pressure tester is new, but its innova which Im not too fond of. I plan to check and clean the injectors, but I'm thinking that the Fuel Pump I replaced might a possible culprit.

I have dual tanks and initially neither tank would function and when I removed the rear tank it was full of rust, had bad seals and the entire fuel pump assembly was falling apart. I haven't taken off the midship tank yet and I'm wondering if I need both tanks sealed and properly functioning to achieve the desired fuel pressure.

Unfortunately in a bit of a youthful learning curve, I have not kept all the motorcraft parts, and I'm starting to realize that I OTC parts are mostly crap. Although each piece replaced makes the truck seem stronger, it never addressed the core issue, which I now know revolves around the fuel pressure.

 

Small update, pulled the fuel injectors, used the truck battery to apply 12 v. 5 functional w/ good spray pattern, 1 unresponsive.

 

When the Machine Shop finished rebuilding my 89 the pump he put in the new (38gal) rear tank was from a Chevy. He handed me both pumps, the Chevy one was significantly heavier and he said it was far superior to the original in-tank F150 pump. I also got matched injectors for the fuel. He did a lot of things that I would not have thought of. This machine shop also builds engines for a place out west that we call the "Salt Flats", and he has a lot of photos on the wall of builds he made for out there.

He was pleased with the fuel system after doing all of his ideas for me. That was a long time ago (not really, but it seems so) and the truck starts like a champ even after being left in the snow for a month this winter. Oh, yes, he also told me to never tap-dance on the foot pedal while starting the engine.

Best of luck with your fuel problem.