95, F150 4.9, 5 speed, 89K miles. ran fine one day next morning hard to start and very rich, fouled plugs.
No check engine light,
scanned no codes
replace plugs, wires, rotor and cap, were original
replace coil original
replaced air sensor in intake manifold, original
removed Catalytic converter, original
checked timing, Ok
Fuel pressure 55 and holds after key is off.
replaced fuel filter, twice.
oxygen sensor at .94 when running
mas air sensor Mhz goes down after start up KOEO 189 mhz
tried a different ecm with the exact same number
Temp sensor and mass air sensor are accutate on surrounding temp.
still running the same, so rich it can't move itself.
cyl, 1 and 4 so rich they miss from start up
wires are correct on cap.
distributer shaft no side play.
4 techs have given up trying to fix.
before this happened MPG was almost 20 that is combination city and interstate.
Does anyone have any suggestions

 

Fuel pressure should only be about 39PSI. Fuel pressure is typically regulated to 39PSI (270kPa) higher than manifold pressure. As idle vacuum lowers the manifold pressure, fuel pressure is lowered to match. The nominal fuel pressure is established by a spring preload applied to the diaphragm. Balancing one side of the diaphragm with manifold vacuum maintains a relative fuel pressure drop across the injectors. If you're running at 55PSI, then you're injecting more fuel than required when the injectors "OPEN" during their 'PULSE" duration.

 

Replace the fuel pressure regulator. Some can be a little difficult to change , but most are easy to get to in order to replace. If you need more assistance let me know.
Hank