Check Valve for the Fuel Pump System

[chicagodude]

Greetings,
I have a 94 Ranger 3.0. I am losing fuel pressure intermittently. I am fairly sure that it losing pressure from the fuel pump/tank. Can you tell me where the check valve is for the fuel pump? Is it possible to replace the check valve?

I put a prsesure gauge on the shrader valve and turned the key on but not start the engine. The pressure goes to 40 and holds after the pump stops. About one time every 7 or 8 tries, the pressure drops fast to zero when the pump stops. I believe it has a bad check valve.

Many thanks for any advice you can give me!

 

[Uncle Gump]

The check valve would be the fuel pressure regulator.

 

[chicagodude]

Thanks Uncle Gump,
I pulled off the vacuum hose to the regulator and did't see any gas in the hose. From what I gather if that's bad, there will be gas in the hose or regulator. Should there be gas in it if it's bad?

 

[alwaysFlOoReD]

I was under the impression the check valve is integral with the fuel pump.

 

[Dirtman]

Before you go nuts... don't know if you tried this or not, just throwing it out there. Have you checked that an injector isn't sticking? Easy test. Let the truck sit a few hours, hold the accelerator to the floor and try to start the engine. If it fires a bit then stops fuel is leaking into the cylinder from an injector.

 

[chicagodude]

I never tried that Dirtman. I'll give it a shot tomorrow. Too late for me right now.

It stalled on me four times when I was out running errands. It would just stop running while driving. I pulled over and after a 10 or 15 minutes it would start again and then go a couple miles and quit again. I finally made it home after all that.

 

[snoranger]

I never tried that Dirtman. I'll give it a shot tomorrow. Too late for me right now.

It stalled on me four times when I was out running errands. It would just stop running while driving. I pulled over and after a 10 or 15 minutes it would start again and then go a couple miles and quit again. I finally made it home after all that.

A bad check valve is at the beginning of the pressure system. It stops fuel from returning to the tank through the pump when it's not making pressure. Anytime the pump is running, the check valve is pretty much useless. A bad check valve wouldn't cause an engine to stall.
A regulator is the end of the pressure system and the start of the return. It can leak into the vacuum line or through the return to tank. (It can also leak externally, but you'd probably see/smell that.)

 

[RonD]

Yes, as AlwaysFloored said the check valve is part of the fuel pump not a separate changeable part, its basically just a flap that's pushed open when pump is on and then closes when pump is off, so fuel can't flow back into the pump, nothing fancy

1997 and older also had a fuel pressure regulator(FPR) on the engine end of the fuel system, its a valve with a spring that holds it closed, spring is set for about 42psi
So under 42 psi spring is strong enough to hold valve closed, at 43psi spring is pushed open until pressure is under 42psi again, this is not an EXACT pressure system, lol, about 42psi.

A vacuum hose is added to the FPR to stabilize pressure at a lower level; when engine is idling vacuum is high and fuel demand is low, under acceleration vacuum is low and fuel demand is high
So by adding the vacuum line "we" get a stable pressure of about 35psi engine running at ANY RPM or fuel demand
30-38psi is normal, engine running, pressure

Yes, FPR can leak fuel into the vacuum line, causing Rich running, and would need to be replaced, but its spring can also fail causing lower pressure or 0 pressure key off
Pull off the fuel return line from the FPR and put a towel down under that port, cycle key on and see if FPR is leaking pressure under 42psi

If not then pressure is being lost at the check valve(fuel pump)

Leaking injector would cause running issues, Rich running and misfire from the cylinder closest to that injector

Your symptoms read like a dirty fuel filter or..................more likely a failing fuel pump

 

[chicagodude]

Thanks guys for all of your valuable knowledge! I appreciate it very much!

RonD, could a leaky injector causing it to stall?

Dirtman, I gave it a cold start with pedal to the floor. It started but didn't sputter. Whatever has been happening is intermittent so one test may not determine anything. I'll try it again next cold start.

I replaced the fuel pump today but the jury is still out on whether it's fixed. I ran it while parked two separate times for about 15 minutes with no stalling which is a good sign. I'm going to do more pressure testing and I'll report back with the results.

I never had an electric fuel pump fail before. I had two of the old mechanical fuel pumps fail and both of those caused stalls and then would run OK again for a while before the next stall. About the same thing that happened with this one. Hopefully the new fuel pump did the trick.

 

[chicagodude]

Dirtman, sorry I wrote that wrong, with pedal to the floor it doesn't start.

I took the old fuel pump and connected it to a 14V power supply with a hose connected to the pump output. I then put the pump in a bucket with water. I let the pump run for a while and recirculate the water. After about 10 minutes the pressure dropped to very low and you could hear the sound of the pump sporadically fluctuating. It would occasionally stop and then start again. see the attached pictures.

In the second picture you can see the water coming out pretty slow. When the pump is cold, it pumps out a lot more water. It looks like the problem is heat-related. When the pump heats up, it starts messing up. I rigged up this test to confirm the old pump is bad before I take the Ranger out again. It sucks being stuck on the side of the road.

When I checked the pressure with the new pump installed, it shows about 40 PSI after turning the key on but not starting the engine. With the engine running the pressure is about 33 to 34 PSI.

 

[chicagodude]

RonD,
I see that you also have a 94 Ranger. Can you do me a favor and look at the pipe in my picture below. When I was working on the fuel testing, I found a hole in the pipe. It's a pretty clean hole about the size of a #10 screw size. I put a self-tapping #10 screw in it to plug it up. You can see the screw, I put a red circle around it.

I'm not sure what that pipe is called. It's on the driver's side just under the brake booster check valve hose. See attached pic.

Please look at the pipe on your Ranger and tell me what belongs in that hole. Thanks in advance!

 

[RonD]

Thats the EGR pipe, my 1994 4.0l doesn't have an EGR system

I think just Calif models did, but not sure of all other states

 

[chicagodude]

Thanks RonD!