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2003 5.3L Silverado Fuel Pump

2408 Views 5 Replies 3 Participants Last post by  DDTanner
I have had a problem with idle being low at 500 RPM's in drive. It drives fine at driving speeds then suddenly has started idling rough and the engine light started flashing. I then checked for any DTC's and kept kicking out P0300 DTC which is a random misfire. I changed spark plugs checked the plug wires and has great spark from all cylinders. I then started on the fuel system by changing fuel filter and nothing seemed to be working. I was about to change the Fuel Pressure Regulator and took a fuel pressure reading first. When turning the ignition on, it jumps to 60 psi. Then I started the enigine and it ran at 50psi and when reving the enigine it would go up to near 60 psi then drop to 48psi. What I did not notice at first is when turning the idnition to the on postition it would start out at 60 psi then drip to 9 psi within 1 minute.

I assume this would be the fuel pump nd not the FPR with it not holding pressure with the ignition on. anyone have any problems with the fuel pressure dropping to 9 psi with ingnition on?
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I would replace the regulator anyway as it is 10 years old, and with good eng off key on of 60 psi this would be a good thing to change. 48 psi is too low I would like to see 53-57 psi at idle.

remember idle low vac high more vac the lower the fuel pressure. at idle the reg drops pressures. with eng off no vac max pressure. so I would say the reg is n/g....
I was thinking that also, if the pressure goes up to 60 psi then drops so quick the regulator should be holding the pressure at about the 60 psi instead of the fuel pump itself. I will change the FPR tomorrow morning and recheck the pressure, I will let you know what it does.

Thank you j cat...
the regulator causes the engine off or WOT condition to create the higher pressures required. at idle the regulator drops the pressure about 5psi. some have had failures where the regulator would drop pressures more than 5 psi at idle then you get problems. the regulator some times will leak into the vac line also as another failure condition.
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