Fuel delivery issues PLZ HELP

[jmanczuk2468]

I have a 2006 ford explorer limited 4wd with the 4.0 motor with 159,000 miles. A couple weeks ago I went to start my car and it cranked but did not fire up like it normally does, so I checked the fuel pump and could not hear it so i checked my fuses and relays, all tested fine so I swapped out my fuel pump and I thought I had fixed the problem at first however two days later I ran into the same issue so I swapped out the inertia switch and the car ran like a champ for the next week and a half up until today. I'm now back at square one with the fuel pump not turning on when I turn the key to the on position. I've checked the fuses relays and inertia switch and crank sensor again and all are good. I am now getting a P0191 code for a fuel rail pressure sensor circuit range / performance. any ideas for diag would be greatly appreciated.

 

[J_C]

Welcome to the forum!

I almost asked if you only replaced the pump or also the whole sending unit to get a new pressure regulator with it, but if you are certain it's not turning on at all, then it seems like it is time to bust out a multimeter and take measurements along the circuit to see where power is lost. Don't forget to check for good ground!

However since it is intermittent, I might first check the relay again, maybe permanently swap it with another relay in same box if there are others of same type, or IF all else fails, replace the relay since they are so inexpensive.

I don't have a wiring diagram for that at the moment but here is one for an older generation Explorer which may be pretty similar (except not same fuse #? IDK). Regardless it helps to visualize that momentarily when the key is turned to the run position, the relay should have for that moment, power getting to pin #1 or 2, and the other of pins #1 or 2, a good ground, and of course power in at pin 3 in the relay socket and then if the relay is plugged back in, power out at pin 5 (though it might be more convenient to check for power at the inertial switch first before trying to access the feed out of the battery junction box).

To clarify, momentarily only means that, keeping the key in the run position will not continue to run the fuel pump, until the engine is cranking, so if you don't want to be cranking away a lot and running down the battery, be ready to check for the momentary voltage when then key is turned.

This could be invalid info if the circuit had changed by '06.

Might not hurt to hook up a scan tool too, one that can read live data to see what the fuel pressure reading is, whether the error code is due to it reading correctly, no fuel pressure because the pump isn't running. Forscan app, a cheap ELM327 dongle, and a phone/tablet/laptop/etc host can do that.

 

[Dsc]

Fuel Pressure Driver Module (FPDM) is likely failing. I had the same symptoms and replaced the fuel pump, only to find the FPDM was failing.

 

[J_C]

Fuel Pressure Driver Module (FPDM) is likely failing. I had the same symptoms and replaced the fuel pump, only to find the FPDM was failing.

Do these use a variable speed pump? If so, then the diagram I posted previously is incomplete as it is only applicable to vehicles with an always-on pump with a pressure regulator at constant pressure. Then again I suppose a design could include an always on (full power) pump and the FPDM could vary the fuel pressure via a solenoid or whatever instead. Either way, the diagram I posted is incomplete, could be used as a general guide to see if power stops within the portion of the circuit shown but not if power /control fails elsewhere.

 

[Dsc]

Not sure of which other years but the 2006/7 system used the FPDM to vary pressure of the fuel pump. I believe from what I read it was because of emissions caused when excess fuel was sent to the engine and heated, then returned to the tank caused the increased emissions . The solution was to eliminate the return fuel line and have variable fuel pressure. Many diagrams seem to omit the FPDM when showing the fuel system, maybe due to it being part of emissions, not sure.