Bad fpr??

[Drg1486]

99 Ford Explorer 2wd 4dr 4.0 sohc 121k...

New fuel pump an filter

Cycle the key to even start to get fuel pressure

Once start idles fine no vacuum leaks but at wot intake backfire P0171 lean code

Either fpr or the PCM for the fuel

No other codes .. check /clean iac,Mas,tps,plugs,coils,timming,

Now if there is something i may have missed to check id sure like to know..an if any other info i need to give lmk..thanks

 

[J_C]

Seems like you need a gauge on the fuel rail to tell you the pressure, and after you cycle the key the first time I'd leave it sitting to see if it holds that pressure or drops fast like there's a leak. Otherwise with it happening at WOT I'd wonder if your injectors are partially clogged and a fuel system cleaner product might help.

What order did you do the pump and filter in? I'd be paranoid about residue in the tank after the pump swap and wait a while to put a new filter on, so hopefully any crud left behind gets trapped in the old filter before it's replaced.

 

[Drg1486]

Now would low fuel just about empty a tad off E effect it much on the lean because there isent much fuel in the tank...but ill get a gauge on it too

 

[J_C]

No the pump should still pick up fine so long as fuel isn't so low that it's drawing air, but since you're going to need fuel anyway, might as well put more in. Bad fuel and whatever settles to the bottom of a tank is another possibility that comes to mind.

It's also best in summer, particularly in a hot area like FL, to keep more fuel in the tank as that keeps the pump running cooler by being submerged in it.

What prompted the fuel pump replacement, was there a clear diagnosis it was bad? Was the problem completely fixed with the pump swap then later a new problem or is there possibly the same problem still persisting?

I'm wondering if it was the regulator bad all along, or if there is a problem with the new pump, defective from the factory. It doesn't seem likely but on rare occasions I've gotten some bad parts.

I'm probably speculating too much. I'd put a few gallons in the tank and see if that helps, along with some fuel injector cleaner, drive it a few dozen miles if it runs well enough to do so, then do a fuel rail pressure test if the problem persists.

 

[Drg1486]

Cant drive it yet no tag...an yes old pump was bad tested it...now the new one i had to switch the wires around for neg an pos bc it was makin it run in reverse from the stock plug

the guy i got it from had the same problem thats the reason for selling it spits and sputters when accelerating so as thought oh bad fuel pump had same issue with my F-150 a new fuel pump fix that but it also could be like you said a faulty new pump ..it's just giving enough fuel to let it idle but not enough to hold full PSI at wot..so ill get the gauge an test fuel pressure in the morning

 

[ranger7ltr]

If you actually have a 99 and later Explorer the fpr is in the tank and the ones I have seen will not bypass fuel back to the tank under 80 psi... Plenty of fuel to run your engine... Did the hose between the fpr and the fuel pump get replaced? An aged delivery hose will leak or even split and let fuel spray out before going into the fuel lines... You do need a fp gauge to see what you have... If your rail pressure is not 65-72 psi constantly either it is a defective pump, a rust clogged filter, a leaking or split fuel line from the pump or a combo of all of the above...

Was your tank rusty when you pulled the pump out? I fought a rusty tank for months and finally replaced it and didn't have a rust clogged filter any more...Oh and did you line up the arrow on the pump/sender with the dimple on the tank? If not the pump pickup will not be in the proper spot and it might not pick up fuel with the tank level under 1/4 tank...And the PCM has nothing to do with the pump operation except to supply system voltage to the pump through the relay and the inertia switch...After the initial key on to prime the pump, the PCM senses engine rotation and delivers system voltage... It doesn't vary the pump operation or pressure at all...

 

[Drg1486]

Ok i just want to give update to my problem i had.. I know it's been awhile but.it was the pressure regulator and now it cranks and drives like it should ..thanks to all who help me get it fixed