Fuel Pressure Drop

Okay I have a 2003 Ranger EDGE 3.0 with a hard start and codes popping up for multiple cylinder misfires and #2 misfire. Truck still runs but seems to have a little stumble, mostly at idle, and a little at acceleration. Other than that is seems to run fine. I first checked the fuel pressure and got 65 lbs. (normal) pressure but when I turned off the motor, pressure drops to almost zero very quickly. From what I have read, fuel pressure should not drop that fast, or should it. Most websites I visited say it could be a bad check valve on the fuel pump, leaky injector(s), or a bad fuel pressure regulator. Since everything outside of the injectors are located inside the tank was wondering if anyone has had or seen this problem before. Since there is no return line and the main line is solid, I don't think I can pinch off this line to isolate the rail to see if the leak is there. Was hoping to avoid replacing parts (i.e fuel pump, regulator, etc.) and pulling the bed unless I know it's really inside the tank. Is there a way to check the injectors for leakage, seems like if I can eliminate them then must be the pump or regulator.

The fuel system should hold pressure for MONTHS, not minutes, hours or days, MONTHS

If 65psi running then it should hold above 40psi, key off, for many months

Yes, on the 1998 and up Rangers it is usually a bad check valve inside the fuel pump, it is part of the pump not a separate piece.
1997 and earlier have fuel pressure regulators and they could also leak, you do not.
Although......check your fuel filter(in frame under drivers seat area), if it has 3 hoses then try replacing it, it can also cause loss of pressure back to gas tank

Yes, you can check for leaking injector easily.
All fuel injection computers have a "Clear Flooded Engine" mode
It is:
Key on
Press gas pedal down to the floor and hold it down all the way
With 0 RPMs(engine off) and throttle sensor at Wide Open(WOT) Computer will shut off fuel injectors

Holding gas pedal down all the way, crank engine

Engine should NOT start, it should not fire at all, fuel injectors are OFF
If it fires or starts then a fuel injector is leaking
As soon as RPMs get above 200 fuel injectors will start up, default
As soon as you release gas pedal fuel injectors will restart, ends Clear Flooded Engine mode

I use this daily so I can pump oil thru the engine for a few seconds before startup.


If your engine fires during test then you can find leaking injector using the same test
Cold engine this time makes things easier
Unplug Coil packs connector, you want a No Spark, No Start
Repeat above test, but crank it a few times, gas pedal held down all the way
Now start pulling out spark plugs
The WET one has the leaking injector


For temporary quicker starts, cycle key on, count to 3, then key off, repeat 3 times, that should give you about 45psi fuel pressure, then try to start engine.
Each time key is turned on, computer primes fuel system for 2 seconds, that restores about 15psi of pressure.
So 3 times on/off/on gives about 45psi

Repair Update

Okay finally can post the repair update. I first just installed the Bosch replacement pump that comes with an adapter for the wiring and fuel hose. Car started up and ran, but I still noticed the same fuel pressure drop when I turned off the car (tested with fuel pressure gauge), and after a couple days the truck died out on the freeway. Possibly a bad pump, because the pump would not energize when I checked it. So I decided to just replace the whole sending unit. After this install the fuel pressure held fairly well, after an hour, pressure has only dropped to 50lbs. Maybe a slight leak in another part of the system, but definitely the pressure is holding better than before so the drop must have been with something else on the sending unit (regulator? check valve?). Lesson learned: if the cost is not significantly more, just replace the whole thing instead of trying to save a few bucks, especially when you have to move the whole bed out of the way.

For years mine has not held fuel pressure after the shut off. I put a new pump in in December 2016, still does it. But, it's never affected anything far as I can tell. It starts first turn of the key. It runs great and no codes. So, I just ignore it. I had a fuel pressure gauge tie-wrapped to the radiator hose under the hood after the new pump install. Kept a constant watch on it. Drops to zero almost immediately after shutting off. Starts up the next day first turn of the key. Non-issue.

Heck, fuel pressure doesn't even read when I turn the key on. Nothing. Start it and VROOM, it's running. Holds 62 psi running. Don't know what's wrong, but it doesn't seem to affect it one iota.

I know this is old, but I am having a very similar problem with my 1998 4.0L OHV 4x4 ranger. When you said "decided to just replace the whole sending unit", do you mean you replaced the whole fuel pump?

Very old but at least you searched. It sounds to me like the meant the entire assembly. Pump, sending unit, sock filter, ETC. That would be everything that comes out of the tank when you take the locking ring off the top.