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Home >> GMC >> 1990 >> Forward Control 4.3 Z, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Fuel System Pressure Test >> Fuel Pressure Check
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Fuel Pressure Check

  1. Relieve fuel pressure (if necessary). Remove air cleaner and plug thermal vacuum port on throttle body. When removing fuel line, always use 2 wrenches. Install Fuel Pressure Gauge (J-29658B or BT-8205) and Adapter (29658-85) in fuel line between steel line and flexible hose.
  2. Turn ignition off. Apply battery voltage to fuel pump test connector using a 10 amp. fused jumper wire. Observe fuel pressure reading. Fuel pressure should read between 9-13 psi (.6-.9 kg/cm2 ). If no fuel pressure exist, go to step 3). If fuel pressure is less than 9 psi (.63 kg/cm2 ), go to step 6). If fuel pressure is greater than 13 psi (.91 kg/cm2 ), go to step 7).
  3. Listen for pump operation at fuel tank. If fuel pump is running, check for plugged in-line fuel filer, plugged pump inlet filter, restricted fuel line or leaking pump rubber coupling. If these are okay, replace in-tank fuel pump.
  4. If pump was not operating, disconnect fuel pump relay. Using a 10 amp. fuse jumper wire, connect 12 volts to circuit 120 (Gray wire). If pump now operates, check for faulty connection at relay or faulty fuel pump relay. If pump will not operate, check for faulty in-tank pump or faulty pump ground.
  5. If fuel pressure was less than 9 psi (.63 kg/cm2 ), check for restricted fuel filter or restricted line between in-tank fuel pump and pressure gauge. If fuel filter and lines are okay, go to next step.
  6. Disconnect injector connector. Apply battery voltage to fuel pump test connector. Gradually pinch fuel pressure gauge and note pressure. If pressure is greater than 13 psi (.91 kg/cm2 ), replace fuel pressure regulator. If pressure is less than 9 psi (.63 kg/cm2 ), check for faulty fuel pump or incorrect part. Check coupling hose and pump inlet filter.
  7. Disconnect fused jumper wire from test connector. Disconnect fuel return line quick-connect fitting. Attach 5/16" hose to throttle body side of return line and insert other end of hose in a gasoline container.
  8. Using a fused jumper wire, apply battery voltage to fuel pump test connector. If fuel pressure is greater than 13 psi (.91 kg/cm2 ), check for restricted return line from throttle body. If line is okay, replace fuel pressure regulator. If pressure is between 9-13 psi (.63-.91 kg/cm2 ), correct or replace fuel return line to fuel tank.
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