Code 556 came up on Memory codes - Fuel pump primary circuit malfunction. I need to retest the fuel presure. I think last time it was at 60 but bled off quickly. Fuel pump was replaced several years ago after leaving me on I 75 near Ocala Fl. Does this code sugest replacement of pump again? 186,000 with a strong 4.9. Also I have had poor gas milage. 160 mile to a tank (highway).
Recently ran Seafoam through 2 tanks and hace seen 13-15 mpg around town

 

Not always. The code says primary circuit, not pump.
You need to test and troubleshoot the circuit to see if it is a relay, the inertia switch or the pump or wiring.
The inertia switch and relay should be on the fuse panel.
The fuel pressure should be in the 40 psi range.
The pump normally runs a couple seconds when the ignition is in Run prestart position. Listen for it.

 

Many times, OBD-I codes related to the electrical system for the puel pump are set as a result of an engine stall. In this case, they can likely be ignored if there is no other indication of fuel pump problems.

Was the CEL on in the first place or are you trying to determine what your fuel economy is so poor? Faulty fuel pump action is unlikely to result in poor economy.

Fuel economy is very dependent on driver actions, the vehicle configuration, and the efficiency of the ignition system and airflow systems.

Steve

 

I will retest pump presure I did not think of the inertia switch . I beleive this was locater near feet of passenger side between door and firewall according to salesman in '93. My son wrecked the truck about a year ago. Pump does run during start up but very quiet , not like it used to be. It had been realy pronounced . I will look for the relay as well.

 

to projectSHO89: I do not know what CEL is. I understand what you mean with faulty pump being unlikely cause of poor mileage. I am goin on what the auto store had said. I did not think it should effect it too much. I would have thought it would be acting up like it did in Ocala Fl if pump were failing. Just trying to cover bases. I thought it strange after running Seafoam through the tank that the mileage was better. Leads me tho think that the injectors might have been clogged. I have put a new fuel filter on about 6 months ago wondering if this would help. It did need changing but did not help matters any.

 

Fuel pressure that is too high can cause poor fuel mileage. Ford has had problems with the fuel pressure regulator causing high fuel pressure. Test fuel pressure with the engine running, should be in the 45-50 psi range for the 4.9 engine. Anything higher than that can flood the injectors. BTW, CEL= "check engine light".

 

Thanks about CEL. No CEL . I will check presure again today if possible . Spent yesterday doing emergency Cluch replacement. I got every last mile from the old one.