Fuel System Pressure Test: MFI

Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Connect Fuel Pressure Gauge (J 34730-1) to fuel pressure test port on fuel rail. Turn A/C off. Turn off ignition for 10 seconds, then turn ignition back on. Fuel pump should operate for about 2 seconds. Cycle ignition on one more time to obtain maximum pressure.
Fuel pressure with fuel pump running should be 41-47 psi (2.9-3.3 kg/cm² ). Turn ignition off. Fuel pressure may drop slightly but should hold steady. If fuel pressure is within range, go to step 4). If fuel pressure is within normal range but drops off during acceleration, cruise or hard cornering, go to step 10). If fuel pressure is okay, but does not hold, go to step 5). If fuel pressure is not as specified, go to step 7). If fuel pressure is not present, go to next step.
Ensure fuel pump circuit is okay. See FUEL SYSTEM (MFI) under NO START - ENGINE CRANKS OKAY (3.8L WITH C(3)I) . If fuel pump circuit is okay, check for plugged fuel filter, restricted fuel line, plugged fuel pump strainer or leaking fuel pulse damper. If all checked okay, replace fuel pump.
Start and warm engine to normal operating temperature. At idle, recorded fuel pressure should drop to about 3-10 psi (.2-.7 kg/cm² ). If fuel pressure does not drop, disconnect vacuum hose from pressure regulator. Apply 12-14 in. Hg to pressure regulator with engine at idle. If fuel pressure drops to about 3-10 psi (.2-.7 kg/cm² ), check for vacuum leak to pressure regulator. If fuel pressure did not drop, replace fuel pressure regulator.
Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Install Fuel Pipe Shut-Off Adaptor (J 37287) between fuel line and fuel rail. Leave valves open in adaptors. Using a fused jumper wire connected to battery voltage, jumper fuel pump test connector and wait for fuel pressure to build up. Disconnect jumper wire. Close adaptor valve in fuel feed line. Fuel pressure should hold. If fuel pressure does not hold, go to next step.
Check for leaking fuel pulse damper. If damper is okay, replace fuel pump (check ball inside pump is leaking). If fuel pressure does not hold, open adaptor valve in fuel feed pipe. Reconnect jumper wire and wait for pressure to build up. Disconnect jumper wire and close adaptor valve in fuel return line. If pressure holds, replace fuel pressure regulator. If fuel pressure does not hold, check for leaky injector(s).
If fuel pressure is greater than 47 psi (3.3 kg/cm² ), go to step 9). If fuel pressure is less than 41 psi (2.9 kg/cm² ), turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Install Fuel Pipe Shut-Off Adaptor (J 37287) between fuel line and fuel rail. Leave adaptor valve open. Using a fused jumper wire, jumper fuel pump test connector to battery voltage. Slowly close adaptor valve. Watch fuel pressure. DO NOT exceed 60 psi (4.2 kg/cm² ).
If fuel pressure increases to greater than 47 psi (3.3 kg/cm² ), replace fuel pressure regulator. If fuel pressure did not increase, check for restricted fuel pump strainer, leaking pulse damper, or wrong or faulty fuel pump.
Turn ignition off. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF . Disconnect return line from fuel rail. Connect a flexible fuel hose to fuel rail return pipe and place hose end into a container. Turn ignition on. If fuel pressure is 41-47 psi (2.9-3.3 kg/cm² ), check for fuel restriction in return line to fuel tank. If fuel pressure is not as specified, check for restricted fuel rail return pipe. If there is no restriction, check for restricted filter screen inside pressure regulator or check for faulty pressure regulator.
Check for restricted fuel filter or fuel feed pipe. Repair as necessary. If restriction is not present, check for restricted fuel pump strainer, leaking fuel pulse damper or faulty fuel pump.