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I posted some info on my 92 f150, 5.0 a month or so ago.When checking the fuel pressure with the key on,the pressure goes to 40 psi,but when the pump disengages it immediately falls to zero(in 2 seconds or so).I also have some drivability issues and rough idle at times,along with a strong gas smell at idle..Exhaust pipe tips are black as coal..It has been said that the injectors leaking could cause, or is the problem..Does anyone else know of any other condition that could cause this problem???One last note,the engine usually has to be cranked over several times before it will start,and if you get on it ,for example passing a car,it will backfire....I appreciate any help i can get.....
Have you checked the fuel pressure regulator for a ruptured diaphragm? Pull the vacuum hose and if there is fuel in the vacuum line, it is time for a new pressure regulator, even though it still maintains the correct static fuel pressure.
Yes the fp regulator was changed by myself,and then under recall by my local ford dealer,they also placed a check valve in line somewhere,to keep fuel from bleeding from one tank to the other....
Well the front tank is a new ballgame,the pump runs but no pressure to the rail,therefore it will not start, I have always just run on the rear tank.....
It could be the fuel pump, or it could be a stuck-open injector, or it could be the fuel pressure regulator (which you have already replaced). Have you taken any of the plugs out to see what they look like? If one is more carboned up than the rest, there may be a problem with that one cylinder, either injector or something else. The fuel pump has a check valve inside it to both prevent fuel from going from the running pump backwards into the inactive tank and also to maintain fuel pressure after shut down.
I think I would track down the fuel pressure problem first, then the rich running condition may solve itself. That could save you from spending money to replace various sensors that may still be working properly.
^ I agree. You need to find out where your loosing your residule fuel pressure. I would start at the pump in the front tank. It sounds like the check valve in that pump may be bad.
Do you have any codes coming up in the computer? If all the plugs look the same, I would think that it's not the injectors. And you've double checked that there's no fuel in the fuel pressure regulator vacuum line?