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My OBD shows that I have low fuel pressure in a 1997 Ford Mercury (tracer). Do I have to replace the fuel pump? If so, do I have to replace the whole thing or is it enough to replace just the motor unit? What else might cause low fuel pressure reading?

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I am not familiar with a code or a data output that measures fuel pressure on the OBD system. If it's a code what's the code, if not is it a data point that simply says low fuel pressure, or does it give a valve? Also please include the engine size in your question. – Move More Comments Link To Top Jul 31 '11 at 19:29

Generally speaking (not familiar with that model), it could be due to:

  • Bad fuel pump (fairly rare, fuel pumps are one thing that usually last forever)
  • Clogged fuel filter (has it been changed recently/ever?)
  • Bad fuel pressure regulator (although, they usually fail the opposite way)
  • Leaking fuel injectors (unlikely, would require a pump that's marginal to begin with)
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I'd change the fuel filter first, that one is often overlooked... – Timo Geusch Aug 2 '11 at 19:29

The 97 Mercury Tracer doesn't use a Fuel Rail Pressure sensor and any reading you're getting from your OBD2 application is false.

If you believe that the fuel pressure is low, hook up a fuel pressure gauge and verify before replacing anything.

Refer to Brian Knoblauch's answer for potential causes.

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