Question

1997 Buick Park Avenue Ultra 3.8L SC with code p0171

Hi Reynaldo

I replaced the fuel filter. At the start fuel pressure is at 50 psi.
Idle fuel pressure does not stay at 50 psi. Idle fuel pressure is down to 31 psi.
I replaced the fuel pressure regulator and the reading is the same.

Thanks in advance

Answer 1

This is normal, when you first start the vehicle 50 psi,For 2 second the high speed fuel pump is used to prime the system when you turn the key on, Then when the vehicle starts the fuel pump control module is reduced for low speed operation,The test we did was for leakage at the fuel regulator obviuosly it in good condition, The only test is to determine if the high speed fuel pump module is doing its job during boost. There is 2 ways to test the module ,the best way is voltage at the fuel pump, at idle it should be at 8 volts this is for low speed operation at high speed operation it goes to 12 volts there you should have the 50 psi. Dont replace anything lets just test. You can use the fuel pump guage, if somehow you are able to tape it to the window and do a test drive(make sure there is no leak) you should have about 30 psi (this is the low pump operation) The boost you should see 50 psi. Another way is to use voltage measurement at the fuel pump at idle or low speed operation you should have 8 volts and when you boost or high speed operation the voltage should go to 12 volts. If these are correct .There is nothing wrong with the high speed module, (eve though its a popular failure) P.S There are 2 different places for the fuel pump control module if its not mounted in the trunk behind right side trim panel,Then it has to be at the left hand center behind the rear seat.When you find the fuel module you sould see a grey wire this is the high speed , when you first turn the key on this should have 12 volts and also when you boost,The pink wire is the low speed, at idle you should have 8 volts.