Fuel Pressure 101 - Mini-Diary Fuel Pressure Regulator Test Fuel Pump Test

[MrShorty]

[MENTION=287446]whitemfox[/MENTION]: The coil side of the fuel pump relay should have power whenever the key is on. The main fuel pump side of the fuel pump relay should be hot at all times. So, with the key on, there should be two leads at the fuel pump relay that show 12 V. At this point, I would suggest getting a wiring diagram (even the one in Chiltons/Haynes or the free one from autozone's website), then identifying which leads at the fuel pump relay have power KOEO. Then, diagnose further based on the results of that testing.

 

[NPGuy]

1991 explorer 4.0 fuel pump bleed off speed

Fixed the problem! Fuel injection rubber fuel line and some good clamps.
Pressure comes up to 55 PSI KOEO. Sits at 60 PSI running.
Over the past few hours pressure has settled to 55 PSI.

Working on my 1991 4.0 L the fuel pressure would bleed to zero immediately when the pump stopped so I changed the fuel pressure regulator and fuel filter and the pressure would then come right up to 50 pounds when the key was on and once the pump shut off it would start to drop slowly and will eventually go to zero after a few minutes. Question is book said it should hold above 30 pounds I believe for several minutes.
So I would think it should hold pressure for a long time, any feed back? Was thinking maybe the fuel pump check valve was hanging and leaking by.
Injectors hold, I pulled and tested those and regulator is new and I did not see any leaks so new fuel pump next?

 

[newmab]

Just my two cents. I know its a pain but, check the small piece of rubber line on the pump in the tank. Mine was stock at the time with the oem clamps and they were very loose. Once I put a new piece of line on and new clamps pressure held.

 

[Kevinh71047]

I have a 1993 EXPLORER 4.0 liter mine will crank and run fine for a little bit but whats going on is when my sounds like it might die check engine light comes on. Like today i drove about 30 miles ran ok until i stopped cranked it again the engine light comes on and idles real rough. When i had it running i put it in reverse it died.. Any ideas. Please