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Old 12-13-2015
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I am: michael
Join Date: Feb 2015
Location: Beachwood
Vehicle: 1994 ranger
Drive Type: 4x2
Engine: 3.0
Posts: 34
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Fuel pressure test results

I did a pressure test on my 94 3.0 ranger...235,200 miles and most likely the original fuel pump. KOEO pressure went right up to 40 psi then rapidly went down to 10 psi. KOER a steady 30 psi. Suspect this is the reason I often need to crank the engine over twice to get it started. I'm expecting the fuel pump is on its way out???
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Old 12-13-2015
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I am: Ron Dean
Join Date: Jan 2014
Location: Vancouver, BC
Vehicle: 1994 Ford Ranger
Drive Type: 4x4
Engine: 4.0
Posts: 4,764
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1994 has 2 "check valves" that hold pressure in the system.
Fuel pump has a built in check valve, basically just a flap, when pump is on fuel is pushed out lifting flap, when pump is off flap closes so fuel can't flow back in.

Fuel Pressure Regulator(FPR) is on the fuel rail, it has the fuel return line and a vacuum line attached.
When engine is off a spring inside the FPR holds the valve closed so fuel can't flow out the return line and back to the fuel tank.
When engine starts the engine vacuum pulls open the valve against the spring pressure, allowing fuel to flow back to tank.
At idle vacuum is high and fuel use is low, so most of the fuel flows back to the tank, as RPMs increase(throttle plate opens) the vacuum starts to drop and spring pushes valve closed a bit as fuel demand goes up, nice simple system, if it is working.
FPR is set to maintain 30-40psi of pressure.
Above 50psi a small safety valve can be pushed open so system doesn't over pressurize.

Check FPR's vacuum hose, if it has fuel in it replace FPR.

FPR's usually out lasts fuel pumps so yes it probably is the check valve in the fuel pump, but could also be the FPR.

Cycle key on and off 3 times then try to start engine, that will be a temporary fix.
Ford fuel pump only runs for 2 seconds when key is turned on, then it doesn't start again until engine is running.
Cycling the key on and off 3 times builds up pressure for starting, if it is leaking out as you describe.

If fuel pump itself dies then that's where you stop, no warning usually, no hard to start issue, just driving along and engine dies and won't restart.

Last edited by RonD; 12-13-2015 at 08:54 PM.
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