Using Fluke DMMs for a Quick Check of Fuel Pressure on General Motors Vehicles

1. Place the test leads in the 10 amp position, and the function rotary switch in the DC amp position.
2. With the ignition switched "off," connect the red test lead to battery positive. Do
not let the black lead touch ground.
3. Connect the black lead to fuel pump test terminal. The test terminal is located on the end of about a 4" pigtail on the relay itself. This is typically located in the cowl area of the vehicle. *

Compare readings to chart below. Readings below are with the vehicle battery at 12.4 volts. A small spark is normal.

Fuel System Min-Max Fuel Pressure Normal Draw
TBI 9-13 psig 2-4 amps
PFI 36-41 4-6 amps
CPI 5 5-64 8-9 amps

Lower amperage than chart: usually a no start condition, or long cranking time.
· High resistance in fuel pump harness connectors
· Fuel pump ground, or fuel pump
· Out of fuel in tank
· Pump is cavitating from hot fuel
· Vehicle battery low.

Higher amperage than chart:
· Fuel filter restriction
· Fuel return line restriction

If amperage slowly rises after being connected, a fuel filter should be suspected. Allow pump to run for 30 seconds.

Common sense test: Before condemning any part, repeat the test above on a vehicle with the same fuel system and compare your readings