Fuel pressure relief valve

[gw33gp]

I had a post about a problem I was having when travelling long distances on Interstates. Nothing was resolved and I didn't do any diagnostics because it is running very well on shorter trips.

I decide today to check out a few things to see if I could find any issues. I decided to start with fuel pressure. I found a Shrader valve on the rear of the right fuel rail. Its part of what is called the fuel pressure relieve valve in my Ford Service Manual. I attach my fuel pressure tester to it and turned the ignition switch to 'on' without starting it. The pressure would go up to about 50 psi and immediately drop to 0. I checked for leaks and tightened the connection more to make sure it was not leaking. I still got the same results. I cycled it several times with the same results. Then I started the engine and it ran very bad with misfiring. I then removed the fuel pressure tester and fired it up again. It immediately fired up and ran perfectly.

I don't know what this fuel pressure relief valve is supposed to do. It looks like it is just there to relieve pressure by pressing in on the Shader valve when work is to be done on the fuel system. I see no way for it to release fuel pressure any other way. There is no return line like there would be on a fuel pressure regulator. I am baffled why it ran so bad when I had the fuel pressure tester on it. I forgot to look at the pressure when it was misfiring at idle. I was so startled that I forgot the important part of the diagnostic. If I have time later, I may try that again.

I am seeking any information as to why it would do that.

 

[gw33gp]

OK, I spent a little more time on my Ranger. This time I spent a little more time pumping up pressure by cycling the ignition switch more times. I got the pressure up to around 60 before it dropped back to 0. I have a fairly long hose for my pressure gauge, and I think it was not getting filled the first time I ran my test keeping the fuel pressure to low.

When I fired it up this time it ran a little rough briefly then smoothed out fairly quick with the gauge connected. The pressure went up to a steady 65 psi. When I just the engine off, the pressure immediately dropped to 0 again.

I can't think of anything else other than the one-way valve in the fuel pump that would cause the fuel pressure to drop that fast. If the Fuel Pulse Damper was broken, I would have a serious external leak (which I don't have) or fuel getting into the vacuum system causing a rich condition (which I don't have). If you know of anything else that would cause it, I would like to hear about it.

I don't see any Motorcraft fuel pumps and don't know if they ever made them. Does anyone know what brand the OEM pump is? If not any, recommendation of a good brand?

 

[mr_manny]

Motorcraft does make fuel pumps, and believe they are OEM.
I thought I read that Motorcraft pumps are now made in china...which may affect quality. Bosch makes fuel pumps, which are considered better quality.

I'm not familiar with 2002 rangers, but kinda surprised you don't have a fuel return line. When I googled 2002 ranger fuel pressure regulator, they do pop up.

Generally the causes for fuel pressure dropping to 0 are:
Fuel Pump internal check valve failure.
Fuel Pressure Regulator failure.
Leaky fuel injector(s), but doubt it because of how quickly it fuel pressure drops to zero.

You could try attaching your fuel pressure gauge to the fuel line that goes to your fuel filter (from the tank). This would require an adapter, as the connection is different from the schrader valve. This would eliminate the FPR and fuel injectors from the equation. If you don't have the appropriate adapter, you could try pinching the fuel return line.

If your pressure still drops to zero, it's probably the fuel pumps internal check valve.
Unless your also experiencing trouble starting, after your ranger has been sitting for an hour or so (common symptom to leaky injectors).

HTH