Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSISUZU1996TROOPER S, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 21 (ENGINE CONTROLS - BASIC TESTING - 2.6L 4-CYL)FUEL SYSTEMFUEL PUMP PRESSURE TEST
1996 Isuzu Trooper S, Automatic
Fuel Pump Pressure Test
1996 Isuzu Trooper S, AutomaticSECTION Fuel Pump Pressure Test
WARNING: This page is about a different car, the 1996 Honda Passport. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Begin basic fuel system diagnosis with testing fuel pressure.
- Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Install a fuel pressure gauge between fuel pressure regulator and fuel distributor pipe. See Fig 1 . Bleed air from fuel line going to pressure gauge.
- Unplug fuel pressure regulator Vacuum Switching Valve (VSV) connector on right side fender skirt. This is a 4-wire connector with Black and Blue wires in harness. PCM controls VSV to cut vacuum to fuel pressure regulator during hot engine starts.
- Start engine and measure fuel pressure at idle. Disconnect fuel pressure regulator vacuum hose. Note fuel pressure at idle with vacuum hose disconnected (no vacuum). Fuel pressure should be 42 psi (3.0 kg/cm2 ). See FUEL PUMP PERFORMANCE .
- If fuel pump pressure is low, check for fuel leaks, restrictions in intake side of fuel pump, leaking injectors, faulty pressure regulator or faulty fuel pump. If fuel pressure is high, check for restrictions in return line to tank or faulty pressure regulator. If pressure does not change when pressure regulator is disconnected, replace pressure regulator.
- Reconnect pressure regulator vacuum hose and check fuel pressure (with vacuum). Fuel pressure should be 35 psi (2.4 kg/cm2 ). Apply battery voltage to VSV connector Blue wire terminal, and ground Black wire terminal (with vacuum). See Fig 2 . Fuel pressure gauge should read about 42 psi (3.0 kg/cm2 ). If fuel pressure is not within specification, check for defective VSV.
- Disconnect and plug vacuum hose from fuel pressure regulator. Stop engine and ensure fuel pressure remains greater than 35 psi (2.4 kg/cm2 ) for 4 minutes after engine stops.
- If pressure drops, check for leaking injectors, faulty pressure regulator or bad check valve in fuel pump. If engine does not start, by-pass fuel pump relay to check for fuel pressure. Remove fuel pump relay from underhood fuse/relay box. Connect a fused jumper wire between terminals No. 1 and 3 of fuel pump relay connector in fuse block. See Fig 3 and Fig 4 .
- If fuel pump does not operate, check for battery voltage to terminal No. 3. If battery voltage is present, check for open in fuel pump circuit. If fuel pump operates with jumper wire installed, check fuel pump relay and relay energizing circuit. Repair as necessary.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.