1994 Ranger intermitte short


RJC

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Vehicle Year
1994
Make / Model
ford
Transmission
Automatic
New to the board, I have a 1994 ranger 3.0 that was having fuel pressure issue. Hard starting at times. Changed relay worked for couple days and same problem. Put a pressure gauge and had to cycle the ignition 3 times before it got up to 35 psi. changed fuel filter and pump worked another couple days the back to square on. After further research, I found someone with the same problem and ended up to be a bad ground on the relay pin #85. He ran an external jumper ground wire to that pin # and solved his problem. I guess this is a comon problem. I also read that this ground turns relay on and off when ignition is on but when engine is running it stays grounded all the time. My concern is by grounding external constant ground. Would this do any damage to any other components? Any help be greatly appreciated
 


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RonD

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canada
Vehicle Year
1994
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Ford
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Manual
Welcome to TRS :)

Pins 86 and 85 on automotive Relays power the relay coil, when power is FLOWING thru the coil it becomes a magnet and pull down the Relay's metal bar, closing relay contacts 30 and 87, sending another power source thru, turning on something.


The Computer Grounds the Fuel Pump relay, and while it is not common the connection under the relay can get corroded.
Check that first.
Computer grounds the FP relay for only 2 seconds when key is turned on.

It won't ground the FP relay full time until engine RPMs are above 400, engine started, this is a safety feature, if fuel line should break or engine should otherwise stop, accident, the fuel pump won't continue to pump fuel out causing a fire.

Check the FP relays socket wiring.

To answer the question, yes you can manually ground pin 85.
FP relay doesn't have power until key is turned on, so it won't drain battery or hurt anything, unless you leave the key on for long periods without engine running.

Fuel pressure should hold for a few months with engine off.
Running fuel pump for those 2 seconds should get +10psi, and fuel pressure after shutting off the engine should drop to 20-25psi and stay there.
So the 2 seconds would put pressure at 30-35psi for starting.

There are 3 places for fuel pressure to bleed off, assuming you do not smell gas from leaking fuel line.

Check valve in fuel pump
Fuel Pressure regulator(FPR) on the fuel rail
Fuel injector leaking

FPR is a valve that is connected to fuel return line, if it is leaking then pressure is lost by fuel leaking back into the fuel tank, so no smell
 


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