The average fuel pressure for this systems is between 12 psi, and no more than 15 psi.
If once you test the fuel pressure as we are going to show you below, your reading is below 12 psi, the way to know if the problem is in the fuel pump or the fuel pressure regulator is to block the return line, by pinching the rubber hose in the return line with needle nose locking pliers, by doing this you will stop gasoline from flowing back to the fuel tank, this should cause the fuel pressure to increase a minimum of 10 psi, if the pressure doesn't increase, the problem is in the fuel pump and needs to be replaced.
If once you block the return line the pressure increases 10 psi or more the low fuel pressure is likely to be caused by a defective fuel pressure regulator.
Follow the steps below to learn how to test the fuel pressure in a GM TBI fuel injected system.
- Remove the filter as described in our page:
removing the fuel filter.
- We purchased this adapter from MAC Tools, this tool needs to be installed in place of the fuel filter.
Once you have the fuel filter removed, lubricate the o-ring seals in the fuel lines with petroleum jelly, next proceed to install the fuel line adapter and tighten it by hand.
- Using two wrenches , hold the adapter with one wrench, and tighten the line with the other wrench.
- Proceed to install the fuel pressure gauge.
- Next start the car, allow it to idle and check the fuel pressure, as you can see in this picture, the fuel pressure in the vehicle being tested is 14 psi. that is perfect!!.
- If your fuel pressure is below 12 psi, block the return line as we described in the beginning of this page, if the pressure goes up with the line blocked, the problem is a bad fuel pressure regulator, if the pressure doesn't go up, the problem is a bad fuel pump.