Jim Grant's Tech Tips
'83 Ford Crown Victoria, Low Fuel Pressure
Q: I own an ‘83 Ford Crown Victoria with a 5.0 liter engine and automatic transmission. At idle the fuel pressure is at 40 psi at the test port. As the throttle is opened and engine is accelerated pressure drops to around 10 psi, causing the engine to stumble and on the road of course drastically losing power. The problem seems to improve with a greater quantity of fuel in the tank. The fuel pump has been changed two times along with the fuel filters with no improvement of the problem. Hope you can help me out with this problem.
- Donald Holmes
A: Any fuel injected vehicle that has that kind of a fuel pressure drop is going to run poorly if at all. With 2 new fuel pumps and the same problem you should be checking the power supply and ground to the fuel pump. Your vehicle is old enough that the relay or wiring could have a resistance problem. To prove or disprove this have your technician perform a voltage drop test on the power supply and ground for the fuel pump. Ideally, he/she should not see more than 500 to 700 mV drop of voltage across the circuit. If the voltage drop test proves the electrical circuits to be okay then check for damaged or restricted fuel lines. A pinched or kinked fuel line will restrict fuel flow. At idle the engine needs very little fuel. But under load fuel demand jumps, if the fuel line has a restriction the fuel pressure will drop. Your type of problem requires some creative diagnosis. A tech that knows his/her way around a fuel system will know just what to do.