K 1500 Suburban 4WD V8-393 6.5L DSL Turbo (1994)
Fuel Pump Relay Circuit Diagnosis
CIRCUIT DESCRIPTION
When the ignition switch is in the CRANK position, the lift pump circuit is completed through the relay contacts. During this time, oil pressure is
building to the point of closing the contacts of the oil pressure switch. A minimum of 28 kPa (4 psi) is required to close the switch contacts.
When the ignition is returned to the RUN position, the oil pressure of the running engine maintains electrical power to the lift pump.
CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This procedure applies direct voltage to run the fuel pump. If the pump runs, it may be a fuel pump relay circuit problem which the following step
will locate.
2. This step checks voltage from the battery and the ground circuit to the relay.
3. This test determines if there is voltage from the PCM, terminal "A" to terminal "D" on the relay connector.
4. This completes the fuel pump relay circuit, but the oil pressure switch should also be diagnosed.
DIAGNOSTIC AIDS
If engine oil pressure drops below 28 kPa (4 psi), the engine will run poorly or stall when the lift pump circuit opens.
