Mechanics

WOULD A BAD FUEL PRESSURE REGULATOR CAUSE A CAR NOT TO START ?

1995 Mazda 626 • 130,000 miles

Got a 1995 Mazda 626, 4 cyl.
Got off highway one day, car would not stay started at stop signs (at idle) "unless" I give it gas.
Changed air filter. Car ran normally for 2 days, then would not stay started at idle again.
After about every 3 days the idle symptom would go away, work fine for 3 days, then return. This went on for about
a total of one month. Then;
Adjusted the Throttle Position Sensor and car ran normally for about 1 week straight. Then;
Idle issue returned, but this time worse than ever. Looked under hood and noticed the Fuel Pressure Regulator had
malfunctioned and was sending fuel into it's adjoining vacuum line.
Replaced Fuel Pressure Regulator with one from salvage yard.
Now car will crank, but will not start at all?

This replacement (but used) regulator does not shoot fuel into the vacuum sys, but could it still be bad? How can I figure out if it is in fact bad?

I'm down to the Fuel Pressure Regulator or Throttle Position Sensor.

Any suggestions?

P.S. I opened the rail right above the fuel injectors; fuel DOES shoot out when I crank the engine. However, it does NOT come out when the key is in the "ON" position. Also, put spark plug and wire to ground and spark IS present.
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EngymassX
June 23, 2012.




The fuel pump will come on for 2 seconds when the key is initially put in the, "ON" position to prime the system. It will not pump any more unless you repeat the step.
From what you describe it sounds like the Idle air Control Valve was having issues. But, now that it won't start, it is possible that the fuel pump may be going. Try to see what the fuel pressure is when you cycle it. It should be around 45 PSI.
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Ok. I don't get "any" fuel flow when the key is in the ON position, only when the key is in START is when I get fuel flow.

The fuel pressure cycles between 39-44 psi as the engine is 'turning', but without the car actually starting. I unplugged the vacuum line on the fuel pressure regulator, tried to start car and got the exact same fuel pressure readings as when the FPR vac. Line is plugged in (if that bit of info helps).

This is a strange issue with this car.

Tiny
EngymassX
Jul 22, 2012.
The regulator or the vacuum line could be leaking. Pressure should go up with engine RPMs to feed motor. So, something is wrong there.


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