Fuel pressure low & leak down
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Senior Member
Joined: Jun 2005
Posts: 134
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Fuel pressure low & leak down
Just got a fuel pressure gauge to help determine my ongoing PO171/PO174 issue. Quick recap: cleaned MAF, new fuel filter, recent tuneup.
Symptoms: hard warm restart, lean codes (both set at same time). No driveability issues.
Pressure test results:
Key on, 34 psi. Pressure drops to zero over 30 seconds.
Start, pressure goes to 34, rev motor and increases to upper 30's, but goes back to 34-35 psi (acts like it's regulated). Never over 40 psi.
Shut off, and pressure drops fast, about 30 seconds to zero.
So, my conclusion is leaking fuel pump check valve.
Not sure how to cut return line to check regulator, but since the pressure does not go over 40 psi when I bring the rpm's up, I'm not suspecting the regulator. No leaks, either. No vac leak, no fuel in vac line.
Make sense?
Thanks!
Symptoms: hard warm restart, lean codes (both set at same time). No driveability issues.
Pressure test results:
Key on, 34 psi. Pressure drops to zero over 30 seconds.
Start, pressure goes to 34, rev motor and increases to upper 30's, but goes back to 34-35 psi (acts like it's regulated). Never over 40 psi.
Shut off, and pressure drops fast, about 30 seconds to zero.
So, my conclusion is leaking fuel pump check valve.
Not sure how to cut return line to check regulator, but since the pressure does not go over 40 psi when I bring the rpm's up, I'm not suspecting the regulator. No leaks, either. No vac leak, no fuel in vac line.
Make sense?
Thanks!
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
While the fuel pump check valve may not be holding pressure very long after shut down, you need to look at the fuel trim tables for verification that there may be an air leak causing the lean codes.
Don't be focused on just one cause for the codes.
As for the fuel pump, if the pressure comes up right away on cranking, you need not address the pump or regulator just yet.
The pressure won't go over what the regulator allows.
Revving the motor won't cause a large rise because you still have intake tract vacuum holding the pressure down.
The better way is to remove vacuum hose off the regulator and see what level the pressure goes to. If it move upward then comes back when vacuum is re-supplied, the regulator is working ok.
Look for intake air leaks from rubber fitting and hoses and correct for the codes first, then decide if you want to replace the fuel pump inside the tank..
Good luck.
.
Don't be focused on just one cause for the codes.
As for the fuel pump, if the pressure comes up right away on cranking, you need not address the pump or regulator just yet.
The pressure won't go over what the regulator allows.
Revving the motor won't cause a large rise because you still have intake tract vacuum holding the pressure down.
The better way is to remove vacuum hose off the regulator and see what level the pressure goes to. If it move upward then comes back when vacuum is re-supplied, the regulator is working ok.
Look for intake air leaks from rubber fitting and hoses and correct for the codes first, then decide if you want to replace the fuel pump inside the tank..
Good luck.
.
