i was wondering does any one know what fuel pressure is supposed to be for a 1996 F-150 with the six cyl. with key off and when engine running my wifes truck is having a bit of a drivability problem and i just whant to start there any help would be appreciated thanks

 

The specs for a 1993 4.9L are KOEO: 50-60PSI, Idle: 30-45. I don't think the system changed at all between '92 and '96 so those specs should be accurate.

If you have any questions about diagnosing the problem post them here. I have a book called "Ford Fuel Injection & Electronic Engine Control" And it shows all the different tests and specs.


-Jon

 

Actually, that's not quite right. The KOEO specs are 50-60, but the idle specs are 45-60.

What you really need to check is the difference in pressure with and without the vacuum hose disconnected and plugged from the regulator at idle. With it removed and plugged, the pressure should go up about 5 psi.

Also, once the engine is shut off, watch the gauge. It should not move for at least a minute.

Take care,
~Chris

 

well yea i have the book on my 1992 but didnt know if it was the same but it is the fuel pump put my pressure gauge on and taped it to my windshield and when it would act up my pressure would drop to about 27psi replaced the pump yesterday and havent had a problem since exept for those damn fuel lines on the top of the tank those are a bitch when you cant get your hand in there but always appreciate your guys quik replies thanks again ill be talking to ya

 

If you replaced the in tank pump, and it is like the '89 system, it has nothing to do with the fuel pressure at the fuel rail, directly at least. Fuel rail pressure for a 4.9L should be 45-60psi or 50-60 as previously stated when taken at the fuel rail. This pressure is developed by a pump mounted to the frame rail under the drivers side compartment on many applications. The fuel is delivered to a small reservoir just behind the midship pump via the low pressure in tank pumps (8-10 psi). Ford states that, "It has been obsereved that if the low pressure pump is running, it is almost certain that it is operating correctly." So basically, they almost always either work or dont, even though they make excess noise. The in tank pump would only affect the fuel rail pressure in this system if it were not supplying enough fuel to the midship reservoir. If fuel rail pressure is below 45 psi the culprit is likely your midship fuel pump or the pressure regulator on the fuel. If your pressure is low at the fuel rail, check filter, kinked or restricted lines, voltage to midship pump (should be within .5 volts of battery voltage at connector on pump). Also, disconnect return line and note if fuel is being returned through the regulator under low fuel rail pressure conditions. If so, your regulator is bad and not set to operating pressure.

IF FUEL PRESSURE DROPS AFTER KEY IS TURNED OFF
The pressure should remain within 2psi for 3 minutes after pump is turned off. To determine if it is the regulator, first establish your base KOEO pressure. If pressure drops, detatch the return line and plug it (you can do this under the vehicle or at the regulator). Develop about 50psi in system by activating pump. If the pressure holds, it is the regulator. If not, you have a leak either in the lines or the fuel pump is bleeding off pressure.

All of this information was taken from my '89 ford factory service manual. I have used this info on my own truck and found it to be very useful.
Coreyparker64133@yahoo.com