Engine Controls - Basic Testing - Efi Isuzu Amigo I

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm Input Impedance, unless stated otherwise in test procedure.

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 in the ENGINE PERFORMANCE Section to verify routing and connections (if necessary). Inspect air induction system for vacuum leaks.

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer instruction manual for specific instructions.

DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.

Exhaust System Backpressure

Check exhaust system with vacuum gauge or pressure gauge. Remove O2 sensor or air injection check valve, (if equipped). Connect a 1-10 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.

FUEL SYSTEM PRESSURE RELEASE

Note. On all models, fuel pump relay is located in engine compartment fuse/relay box.

Pickup, Rodeo & Trooper (TBI)

1. Disconnect negative battery cable. Loosen fuel tank filler cap to relieve air pressure.
2. Cover fuel inlet line fitting at throttle body with shop towel. Loosen fitting slowly to catch excess fuel.
3. The internal constant bleed feature of throttle body relieves fuel system pressure when engine is turned off. When fuel stops leaking, tighten fitting. Reconnect negative battery cable.

Except Pickup, Rodeo & Trooper (TBI)

1. Loosen fuel tank filler cap to relieve tank pressure. Remove fuel pump relay from underhood fuse/relay box. Start engine and run until it stalls. Loosen hose clamp of fuel line on side of pressure regulator, coming from fuel line inlet distributor pipe.
2. Cover fuel hose with a shop towel, and slowly pull hose from pressure regulator to relieve fuel pressure. When fuel stops leaking, reinstall hose and clamp.

FUEL PRESSURE & FUEL PUMP RELAY TEST

Note. Basic fuel system diagnosis should begin with testing fuel pressure.

Scheme 65

1. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEM.
2. Install a fuel pressure gauge between fuel pressure regulator and fuel distributor pipe. Bleed air from fuel line going to pressure gauge. (Scheme 65)
3. 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.
4. Start engine. 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 ).
5. 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 too high, check for restrictions in return line to tank or faulty pressure regulator. If fuel pressure did not change when pressure regulator was disconnected, replace pressure regulator.
6. 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 to Black wire terminal (with vacuum). Fuel pressure gauge should read approximately 42 psi (3.0 kg/cm 2 ). If fuel pressure is not within specification, check for defective VSV. (Scheme 66)
7. Disconnect and plug vacuum hose from fuel pressure regulator. Stop engine. Ensure fuel pressure remains more than 35 psi (2.5 kg/cm 2 ) for 4 minutes after engine stops. This is rest fuel pressure.
8. 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.
9. 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 67)and (Scheme 68).
10. 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 required.

Scheme 66

Scheme 67

Fuel Pump Relay (2.6L Amigo, Pickup & Rodeo)

1. Power from charging circuit relay runs through fuse/relay box fuse No. 5 and diode box "A" to energize fuel pump relay. Relay is also energized from diode box "A" through oil pressure switch circuit in case of charging system failure.
2. When energized, fuel pump relay closes power circuit from main fuse No. 1, through fuse No. 2, through fuel pump relay to fuel pump. See WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.
3. To test relay, remove fuel pump relay from fuse/relay box on right fender panel. Using jumper wires ground terminal No. 4 (Black wire) and apply battery voltage to terminal No. 5 (White wire). There should be continuity between terminals No. 1 and 3 with relay energized. If continuity is not present, replace relay. (Scheme 68)

Scheme 68

Fuel Pump Relay (2.6L Trooper)

1. Relay is powered by ignition switch starter circuit. When engine starts, charging circuit powers engine relay, which sends power through fuse No. 12 and to fuel pump relay diodes to energize fuel pump relay. Fuel pump relay then passes power from fuse No. 24 to fuel pump.
2. To test relay, remove front Black relay (relay nearest headlight) from fuse/relay box on left fender. Using jumper wires, ground terminal No. 5 and apply battery voltage to terminal No. 4. Using ohmmeter, check for continuity between terminals No. 1 and 3 with relay energized. If continuity is not present, replace relay. (Scheme 68)

FUEL PUMP PERFORMANCE

Fuel Pressure (2.8L & 3.1L V6)

1. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEM.
2. Install fuel pressure gauge between steel line and flexible hose at throttle body. Start engine, check for leaks and allow engine to idle. Fuel pressure should be 9-13 psi (.62-.91 kg/cm 2 ).
3. If engine will not start, apply battery voltage to fuel pump test terminal connector (Black/Red wire). Test terminal connector is a single wire with a clear-colored connector, located in wiring harness on left fender, under fuse/relay box.
4. If engine still will not start, see DIAGNOSTIC CHARTS, CHART A-3/ENGINE CRANKS BUT WILL NOT RUN, in this article. NOTE: Ensure Code 54 is not set by ECM before going to next step. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.
5. If Code 54 is not set and fuel pump does not read within specification, see DIAGNOSTIC CHARTS, CHART A-7/FUEL SYSTEM DIAGNOSIS, in this article.

Fuel Pump Relay (2.8L & 3.1L V6)

1. Fuel pump relay is powered through the ECM. During cranking, ECM will power fuel pump for 2 seconds or until ECM receives ignition reference signals. If engine does not start within 2 seconds after key is turned on, ECM turns off power to fuel pump.
2. If fuel pump relay fails (setting trouble Code 54), oil pressure switch provides back-up circuit to run fuel pump. Oil pressure switch circuit closes when oil pressure is greater than 4 psi (.28 kg/cm 2 ) and operates fuel pump back-up relay.
3. Fuel pump relay and back-up relay are located in fuse/relay box, in engine compartment. (Scheme 69)and (Scheme 70). Also see Code 54 in appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.

Note. To test fuel pump relay circuit, see DIAGNOSTIC CHARTS, CHART A-7/FUEL SYSTEM DIAGNOSIS, in this article.

Scheme 69

Scheme 70

Ignition System Check

See DIAGNOSTIC CHARTS, C-4B/V6 TROOPER, PICKUP & RODEO.

Ignition Coil

Ensure ignition is off. Remove ignition coil connectors. Connect ohmmeter as shown in TEST 1, TEST 2 and TEST 3. (Scheme 71) Replace coil if faulty.

Scheme 71

Pick-Up Coil

Ensure ignition is off. Remove distributor cap. Connect ohmmeter as shown in TEST 1 and TEST 2. (Scheme 72) Replace pick-up coil if faulty.

Scheme 72

Information is not available from manufacturer.

1. Ensure ignition switch is off. Disconnect ignition coil wiring.
2. Measure primary resistance between terminals "C" and "E". (Scheme 73) Measure secondary resistance between terminals "C" and "D". Measure insulation resistance between terminals "C" and body ground.
3. On all models, resistance should be within specification. See IGNITION COIL RESISTANCE (NON-HEI SYSTEMS) table. Replace coil if resistance is not within specification.

IGNITION COIL RESISTANCE (NON-HEI SYSTEMS) Ohms@68°F (20°C)

Scheme 73

Crank Angle Sensor

Testing information is not available from manufacturer. However, faults in crank angle sensor will set Code 41. See TESTS W/CODES article in the ENGINE PERFORMANCE Section.

Note. A faulty power transistor or circuit will set Code 23, 35 or 54. See TESTS W/CODES article in the ENGINE PERFORMANCE Section.

Power Transistor

1. Ensure ignition is off. Remove coil wire from distributor cap. Attach Spark Tester (J-26792), or, using insulated pliers, hold distributor terminal end of coil wire about 1/4" (5 mm) from metal surface.
2. Disconnect and remove power transistor from under intake manifold. This involves removing right front wheel and rubber inner fender panel cover for access to power transistor.
3. Connect jumper wire between harness connector and power transistor connector on Blue wire terminal. Connect negative end of 1.5-volt "D" battery to other power transistor terminal (Green wire on Amigo, Pickup and Rodeo; Yellow wire on Trooper). (Scheme 74)
4. Connect positive end of 1.5-volt "D" battery to other harness terminal (Yellow wire on Amigo, Pickup and Rodeo; Blue wire on Trooper) Ground power transistor.
5. Turn ignition on with engine off. Disconnect and connect jumper lead at power transistor connector several times. Verify spark is jumping across air gap at spark tester. If spark does not occur, check wiring for continuity or shorts. If wiring is okay, replace power transistor.

Scheme 74

IDLE SPEED & IGNITION TIMING

For adjustment procedures, see D - EFI ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

IDLE SPEED SPECIFICATIONS

IGNITION TIMING (Degrees BTDC@RPM)

CHART A-3, ENGINE CRANKS BUT WON'T RUN (2.8L V6)

Note. Before performing this test, check battery condition, engine cranking speed and tank for adequate fuel. Test numbers refer to test numbers on diagnostic chart.

1. When ignition is turned on, the CHECK ENGINE light should come on. This proves battery voltage and ignition voltage are being supplied to ECM. If NO ALDL data (trouble codes) are displayed on Scan tester, this may be due to ECM problem. See appropriate chart in SELF-DIAGNOSTICS article to diagnose CHECK ENGINE light. If TPS voltage is more than 2.5 volts, engine may be in "clear flood" mode, which will cause starting problems. Engine will not start without ignition reference signals. Scan tester should indicate engine speed (RPM) during cranking.
2. No spark may be caused by one of several components related to ignition system. See IGNITION CHECKS in this article for diagnosing ignition problems related to a no-spark condition.
3. Fuel spray from injectors indicates fuel is available. However, the engine could be severely flooded because of too much fuel.
4. While cranking engine, there should be no fuel spray with injector disconnected. Replace injector if it sprays or drips fuel while disconnected.
5. The fuel pressure will drop after the fuel pump stops due to a controlled bleed in the fuel system. Use of the fuel pressure gauge determines if fuel system pressure is enough for engine to start and run.
6. No fuel spray from injector indicates a faulty fuel system, or no ECM control of injector.
7. This test determines if ignition module is not generating the reference pulse, or if fault is wiring or ECM. Using a test light connected to 12 volts, momentarily touch circuit No. 430 (Yellow/Red wire). A reference pulse should be generated. If injector test light blinks, ECM and wiring are okay.
8. No fuel spray from one injector indicates a faulty fuel injector or no ECM control of injector. If the test light blinks while cranking, ECM control should be considered okay. Ensure test light makes good contact between connector terminals during test. The light may be a little dim when it is blinking because of test light current draw. Brightness of blink is not important.
9. Circuit No. 125 (Black/White) supply ignition voltage to injectors. Probe each connector terminal with test light to ground. There should be a light on at one terminal. If the test light confirms ignition voltage at the connector, ECM injector control circuits No. 467 or 468 may be open. Reconnect injector. Using a test light connected to ground, check at ECM connector terminal D14 or D16. A light at this point indicates injector is shorted. Replace injector and ECM.

Diagnostic Aids

1. 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.
2. An EGR valve sticking open can cause a lean air/fuel ratio during cranking. Unless system enters "clear flood" at first indication of a flooding condition, it can result in a no-start condition.
3. Fuel pressure: Low fuel pressure can result in a very lean air/fuel ratio. See CHART A-7, FUEL SYSTEM DIAGNOSIS.
4. A grounded circuit No. 423 (EST) may cause a no-start condition, or a start-and-stall condition.

Scheme 75

Scheme 76

Scheme 77

CHART A-3, ENGINE CRANKS BUT WON'T RUN (3.1L V6)

Note. Before performing this test, check battery condition, engine cranking speed and tank for adequate fuel. Test numbers refer to test numbers on diagnostic chart.

1. When ignition is turned on, the CHECK ENGINE light should come on. This proves battery voltage and ignition voltage are being supplied to ECM. If NO ALDL data (trouble codes) are displayed on Scan tester, this may be due to ECM problem. Appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section will diagnose CHECK ENGINE light. If TPS voltage is more than 2.5 volts, engine may be in "clear flood" mode, which will cause starting problems. Engine will not start without ignition reference signals. Scan tester should indicate engine speed (RPM) during cranking.
2. No spark may be caused by one of several components related to ignition system. See IGNITION CHECKS in this article for diagnosing ignition problems related to a no-spark condition.
3. Fuel spray from injectors indicates fuel is available. However, the engine could be severely flooded because of too much fuel.
4. While cranking engine, there should be no fuel spray with injector disconnected. Replace injector if it sprays or drips fuel while disconnected.
5. The fuel pressure will drop after the fuel pump stops due to a controlled bleed in the fuel system. Use of the fuel pressure gauge determines if fuel system pressure is enough for engine to start and run.
6. No fuel spray from injector indicates a faulty fuel system, or no ECM control of injector.
7. This test determines if ignition module is not generating the reference pulse, or if fault is wiring or ECM. Using a test light connected to 12 volts, momentarily touch circuit No. B5 (Pink/Black wire). A reference pulse should be generated. If injector test light blinks, ECM and wiring are okay.
8. No fuel spray from one injector indicates a faulty fuel injector or no ECM control of injector. If the test light blinks while cranking, ECM control should be considered okay. Ensure test light makes good contact between connector terminals during test. The light may be a little dim when it is blinking because of test light current draw. Brightness of blink is not important.
9. Circuit No. A6 (Light Green/Red) supply ignition voltage to injectors. Probe each connector terminal with test light to ground. There should be a light on at one terminal. If the test light confirms ignition voltage at the connector, ECM injector control circuits No. D16 or D14 may be open. Reconnect injector. Using a test light connected to ground, check at ECM connector terminal D16 or D14. A light at this point indicates injector is shorted. Replace injector and ECM.

1. 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.
2. An EGR valve sticking open can cause a lean air/fuel ratio during cranking. Unless system enters "clear flood" at first indication of a flooding condition it can result in a no-start condition.
3. Fuel pressure: Low fuel pressure can result in a very lean air/fuel ratio. See CHART A-7, FUEL SYSTEM DIAGNOSIS.
4. A grounded circuit No. 423 (EST) may cause a no-start condition, or a start-and-stall condition.

Scheme 78

Scheme 79

CHART A-7, FUEL SYSTEM DIAGNOSIS (V6)

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

Note. Test numbers refer to test numbers on diagnostic chart.

1. Fuel pressure should be noted while fuel pump is running. Fuel pressure drops immediately after fuel pump stops running due to a controlled bleed in the 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 the pressure drop occurs only while driving, the engine will normally surge, then stop, as pressure begins to drop rapidly.
3. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the fuel pump test terminal, pressure should be 13-18 psi (90-124 kg/cm 2 ).
4. This test determines if the 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 cranks but will not run condition, Code 44 (low pressure), Code 45 (high pressure), engine misfire (may feel like ignition problem), poor fuel economy, loss of power or hesitation.

Scheme 80

Scheme 81

Scheme 82

CHART C-4B, IGN. SYSTEM CHECK (V6 TROOPER, P/U & RODEO)

Note. Test numbers refer to test numbers on diagnostic chart.

1. Two wires are checked to ensure an open is not present in a spark plug wire. If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
2. A spark indicates distributor cap or rotor problem.
3. With ignition on and engine off, there should be battery voltage at module terminals "C" and "+". Low voltage indicates an open or a high resistance circuit from distributor to coil or ignition switch. If terminal "C" voltage was low, but terminal "+" voltage is 10 volts or more, circuit from terminal "C" to ignition coil or ignition coil primary winding is open.
4. Checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off, so voltage will be low, but greater than one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage leaks through module (from the battery to the tachometer terminal).
5. Applying 1.5-8 volts to module terminal "P" should turn on the module. The tachometer terminal voltage should drop to approximately 7-9 volts. This test determines whether the module or coil is faulty, or if the pick-up coil is not generating the proper signal to turn on the module. This test can be performed by using a DC battery with a rating of 1.5-8 volts. The use of the test light is mainly to allow the terminal "P" to be probed more easily. Some digital multimeters can also be used to trigger the module. The voltage in the ohm position can be checked by using a second meter or by checking the manufacturer's specification of the Scan tester being used.
6. This should turn off the module and cause a spark. If no spark occurs, fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. A module tester could determine which is at fault.

Scheme 83

Scheme 84

SUMMARY

If no faults were found while performing BASIC TESTING , proceed to appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no hard codes are present, proceed to H - EFI TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.), or intermittent diagnosis procedures.