Engine Controls - Basic Testing - Efi: Diagnosis Isuzu Rodeo I

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. See VACUUM DIAGRAMS article to verify routing and connections (if necessary). Inspect air induction system for possible vacuum leaks.

FUEL PRESSURE & FUEL PUMP RELAY TEST

Note. Begin basic fuel system diagnosis with testing fuel pressure.

Scheme 1

1. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE. Install a fuel pressure gauge between fuel pressure regulator and fuel distributor pipe. (Scheme 1) Bleed air from fuel line going to pressure gauge.
2. 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. ECM controls VSV to cut vacuum to fuel pressure regulator during hot engine starts.
3. 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/cm 2 ).
4. 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.
5. Reconnect pressure regulator vacuum hose and check fuel pressure (with vacuum). Fuel pressure should be 35 psi (2.5 kg/cm 2 ). Apply battery voltage to VSV connector Blue wire terminal, and ground Black wire terminal (with vacuum). (Scheme 2) Fuel pressure gauge should read approximately 42 psi (3.0 kg/cm 2 ). If fuel pressure is not within specification, check for defective VSV.
6. Disconnect and plug vacuum hose from fuel pressure regulator. Stop engine. Ensure fuel pressure remains greater than 35 psi (2.5 kg/cm 2 ) for 4 minutes after engine stops.
7. 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.
8. Remove fuel pump relay from underhood fuse/relay box. Connect a jumper wire between terminals No. 1 and 3 of fuel pump relay connector in fuse block. (Scheme 3)and (Scheme 4).
9. 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.

Scheme 2

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TROUBLE SHOOTING CHARTS

Note. Trouble shooting charts for 2.6L Amigo, Pickup and Rodeo are not available from manufacturer.

TROUBLE SHOOTING CHART DIRECTORY

Diagnostic Aids

Water or foreign material in fuel can cause a no-start condition during freezing weather. Engine may start after 5 or 6 minutes in a heated shop. Problem may reoccur after being parked overnight in freezing temperatures.

A stuck-open EGR valve can cause lean air/fuel ratio during cranking. Unless system enters "clear flood" mode at first indication of flooding condition, it can result in no-start condition.

Low fuel pressure can result in a very lean air/fuel ratio. See CHART A-7, FUEL SYSTEM PRESSURE TEST (PICKUP 3.1L).

1. A grounded circuit No. 423 (EST) may cause no-start condition or start-and-stall condition.

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If an intermittent problem exists, visually inspect wiring and connectors.

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CHART A-7 - FUEL SYSTEM PRESSURE TEST (PICKUP 3.1L)

If there are no RPM reference pulses, ECM will shut off fuel pump within 2 seconds after ignition is turned on. The fuel pump test terminal (Black/Red wire) is located on left side of engine compartment. When engine is stopped, pump can be turned on by applying battery voltage to test terminal.

Note. Test numbers refer to numbers on diagnostic chart.

1. Fuel pressure should be noted while fuel pump is running. Fuel pressure drops immediately after fuel pump stops running is due to a controlled bleed in fuel system.
2. Low fuel pressure falls into 2 categories: Regulated Pressure Less Than 9 psi (.63 kg/cm 2 ) Amount of fuel to injectors is okay, but pressure is too low. Fuel system will be running lean and may set Code 44. Also exhibits hard starting cold and poor overall performance. Restricted Flow Causing Pressure Drop Normally, a vehicle with a fuel pressure of less than 9 psi (.63 kg/cm 2 ) at idle will not be driveable. However, if pressure drop occurs only while driving, engine will normally surge, then stop, as pressure begins to drop rapidly.
3. Restricting fuel return line allows fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to fuel pump test terminal, pressure should be 13-18 psi (90-124 kg/cm 2 ).
4. This test determines if high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.

Improper fuel system pressure can result in following conditions: engine cranks but will not run, Code 44 (low pressure), Code 45 (high pressure), engine misfire (may feel like ignition problem), poor fuel economy, loss of power or hesitation.

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CHART A-7 - FUEL SYSTEM PRESSURE TEST (RODEO 3.2L & TROOPER)

Fuel pressure control valve controls fuel pressure at 41-46 psi (2.8-3.2 kg/cm 2 ). Excess fuel is returned to fuel tank. When engine is stopped, fuel pump can be energized by jumping fuel pump relay connector with fused jumper.

Note. Test numbers refer to numbers on diagnostic chart.

1. Connect Fuel Pressure Gauge (J-34730-1) or equivalent. Wrap shop towel around fuel pressure tap to absorb spilled fuel when installing gauge. On a correctly functioning fuel system, pressure will not leak down after fuel pump is stopped.
2. While engine is idling, manifold pressure is low (high vacuum). When vacuum is applied to fuel regulator diaphragm, vacuum will result in lower fuel pressure, at approximately 25-30 psi (1.7-2.1 kg/cm 2 ).
3. Application of high vacuum to fuel pressure control valve should result in fuel pressure drop.
4. Fuel pressure leak down may be caused by one of the following: Fuel Pump Check Valve Not Holding Pump Coupling Hose Leaking Fuel Pressure Control Valve Leaking Injector Stuck Open Or Leaking
5. Pressure less than 41 psi (1.7 kg/cm 2 ) may be caused by one of the following: Regulated fuel pressure is too low. System will be running lean and may set diagnostic Code 44. Also, hard cold starting and overall poor performance may occur. Restricted flow is causing a pressure drop. Normally a vehicle with a fuel pressure loss at idle will not be driveable. However, if pressure drop occurs only while driving, engine will surge and then stop as pressure begins to drop rapidly.
6. Restricting fuel return line allows fuel pump pressure to be greater than regulated pressure. When battery voltage is applied to fuel pump relay, pressure should be greater than 65 psi (4.5 kg/cm 2 ).
7. This test determines if high fuel pressure is due to a restricted fuel return line or a fuel pressure control valve problem.

Improper fuel system pressure may contribute to one or all of the following symptoms

1. Engine Cranks, But Will Not Run
2. Diagnostic Code 44 Or 45
3. Cutting Out "Feels" Like Ignition Problem
4. Hesitation, Loss Of Power Or Poor Fuel Economy

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See also:
• ADJUSTMENTS - EFI