Fuel pressure

2005 LINCOLN NAVIGATOR
139,000 MILES • 5.4L • V8 • 2WD • AUTOMATIC
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NOS RAMOS
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  • 1 POST
Hard start. i have changed fuel pump driver module already checked relays everything seems to be working fine. i can hear pump kicking in just not building enough fuel pressure. After i turn key over three times it builds enough pressure to start. any feedback is appreciated.
Jul 16, 2017 at 5:40 AM
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CARADIODOC
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  • 34,321 POSTS
  • ASE Certified Mechanic
The fact it does build sufficient pressure proves the fuel pump is okay. Where I would start is by connecting a fuel pressure gauge, then watching what happens to pressure after you stop the engine. That pressure should hold for days if not weeks. The common cause for a long crank time is a leaking injector. The fuel pump only runs for one second when you turn on the ignition switch. That is not enough time for it to build enough fuel pressure for the engine to run. Cycling the ignition switch three times lets the pump run for three seconds. That will get the pressure high enough. The pump resumes running during engine cranking, but since battery voltage is drawn down a lot by the starter, the fuel pump runs too slowly to build pressure quickly.
Jul 16, 2017 at 8:55 PM
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