1999 Chevrolet Silverado fuel pump pressure

1999 CHEVROLET SILVERADO
140,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC
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SCOTTDARR
  • MEMBER
  • 6 POSTS
im getting codes p0174 and p0171, when temperature is below 30 degrees outside idle is very rough surges up and down,
i have replaced maf sensor, iac, fuel pressure regulator,
when i hook up a fuel pressure test gauge to the fuel line the gauge pressure moves with the surge in idling,
should the pressure be constant from the pump?
Feb 21, 2015 at 11:50 PM
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HMAC300
  • ✓Experienced Mechanic
  • 48,601 POSTS
fuel pressure should be 60-66 psi anything lower gives your problems
Feb 22, 2015 at 12:15 AM
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SCOTTDARR
  • MEMBER
  • 6 POSTS
with ignition on the pressure is at 58, when idling its at 48, my haynes manual says thats ok,
i wodered if the pressure moving up and down with the rough idle meant a pump going bad,
thanks
Feb 22, 2015 at 4:28 AM
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HMAC300
  • ✓Experienced Mechanic
  • 48,601 POSTS
sorry gave you the wrong pressure should be 55-62 psi. if you accelerate and it goes below spec then check for partially plugged fuel filter and or restricted fuel line. it should remain above 55 all the time. code 171 and 174 mean it's running lean so it may be a fuel pressure problem. make sure to check for a vacuum leak like cracked hoses/broken hose off etc.
Feb 22, 2015 at 5:47 AM
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