Engine Controls - Basic Testing - Efi Isuzu Impulse II

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.

FUEL PRESSURE & FUEL PUMP RELAY TESTS

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

Fuel Pressure

1. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEM. Attach Fuel Pressure Gauge Set (J-34730-1) and Adapter (J-35957-1) to outlet side of fuel filter. Disconnect pressure regulator vacuum hose. Turn ignition on. Allow fuel pump to run for about 10 seconds.
2. Fuel system pressure should be about 35-38 psi (2.5-2.7 kg/cm 2 ). Start engine and check for leaks. Connect pressure regulator vacuum hose. If engine will not start, fuel pump relay can be by-passed. Also see DIAGNOSTIC CHARTS, CHART A-3/ENGINE CRANKS BUT WILL NOT RUN, in this article. With engine idling, fuel pressure should be 25-30 psi (1.8-2.1 kg/cm 2 ).

Note. To test fuel pump relay circuit, see DIAGNOSTIC CHARTS, CHART A-5/FUEL PUMP RELAY CIRCUIT, in this article.

Fuel Pump Relay (Non-Turbo)

1. ECM powers relay as long as ECM receives ignition reference signals or starter crank signal. For fuel pump relay location.
2. To run fuel pump without starting engine, remove relay and jumper terminals No. 2 and 4. (Scheme 1)
3. To test relay, use jumper wires to ground terminal No. 4 of relay and apply battery voltage to terminal No. 2 of relay. Using ohmmeter, check for continuity between relay terminals No. 1 and 3. If continuity is not present, replace relay.

Scheme 1

Fuel Pump Relay (Turbo)

ECM powers relay as long as ECM receives ignition reference signals or starter crank signal. Relay should be tested in same way as other relays are tested. (Scheme 2)

Scheme 2

FUEL PUMP PERFORMANCE

Ignition System Check

Refer to DIAGNOSTIC CHARTS, CHART C-4D-3.

Ignition Coil

Information is not available from manufacturer.

Cam Angle Sensor

Information is not available from manufacturer.

Refer to DIAGNOSTIC CHARTS, CHART C-4C NON-TURBO.

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

Pick-Up Coil

Ensure ignition is off. Remove distributor cap. Connect ohmmeter as shown in TEST 1 and TEST 2. (Scheme 4) Replace pick-up coil if faulty.

Scheme 3

Scheme 4

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 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 5)
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 5

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 START (IMPULSE NON-TURBO)

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

1. When ignition is turned on, the CHECK ENGINE light should come ON. This test 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 TESTS W/CODES article in the ENGINE PERFORMANCE Section to diagnose CHECK ENGINE light. If TPS voltage is more than 2.5 volts, engine may be in "clear flood mode", which causes starting problems. Engine will not start without ignition reference signals. Scan tester should indicate engine speed (RPM) during cranking.
2. If engine speed was indicated during cranking, ignition module is receiving a crank signal. No spark in this test indicates ignition module is not triggering coil or there is a secondary ignition problem.
3. Test light should flash, indicating ECM is controlling injectors. Test light brightness is not important.
4. This test determines if ignition module is not generating reference signal, or if wiring or ECM is at fault. By touching and removing test light to battery voltage on circuit No. 430, ignition reference signal should be generated. If engine speed is indicated, ECM and wiring are okay.
5. This checks for ignition voltage at injector harness connector. Disconnect H4 (Gray, 12-pin) connector before probing terminal No. 12. Reconnect connector after test.
6. Checks for open in circuit No. 467 or No. 468 from connector to ECM. Ensure injector harness is connected.
7. Disconnect ECM C-D connector and check injector jumper circuits with a DVOM.

Diagnostic Aids

1. Water or foreign material 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 low air/fuel ratio during cranking. Unless system enters "clear flood" at first indication of a flooding, 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 PRESSURE TEST.

Scheme 6

Scheme 7

Scheme 8

CHART A-3, ENGINE CRANKS BUT WON'T RUN (IMPULSE TURBO)

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

1. When ignition is turned on, the CHECK ENGINE light should come ON. This test 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 TESTS W/CODES article in the ENGINE PERFORMANCE Section to diagnose CHECK ENGINE light. If TPS voltage is more than 2.5 volts, engine may be in "clear flood" mode, which causes starting problems. Engine will not start without ignition reference signals. Scan tester should indicate engine speed (RPM) during cranking.
2. If engine speed was indicated during cranking, ignition module is receiving a crank signal. No spark in this test indicates ignition module is not triggering coil or there is a secondary ignition problem.
3. Test light should flash, indicating ECM is controlling injectors. Test light brightness is not important.
4. This test determines if ignition module is not generating reference signal, or if wiring or ECM is at fault. By touching and removing test light to battery voltage on Yellow/Red wire, ignition reference signal should be generated. If engine speed is indicated, ECM and wiring are okay.
5. This checks for ignition voltage at injector harness connector. Disconnect injector harness connector before probing terminal "B". Reconnect connector after test.
6. Checks for open in Blue/White wire or Blue/Yellow wire from connector to ECM. Ensure injector harness is connected.
7. Disconnect ECM C-D connector and check injector jumper circuits with a DVOM.

1. Water or foreign material 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 low air/fuel ratio during cranking. Unless system enters "clear flood" at first indication of a flooding, 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 PRESSURE TEST.

Scheme 9

Scheme 10

Scheme 11

CHART A-5, FUEL PUMP RELAY CIRCUIT (NON TURBO)

When ignition switch is turned to ON position, ECM activates fuel pump relay to run fuel pump. ECM activates relay as long as it receives ignition reference signals or starter crank signal. If no reference signals are received by ECM within 2 seconds after ignition key is turned on, ECM turns off power to relay.

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

1. If fuse is blown, this test checks for short to ground on circuit No. 120. To prevent misdiagnosis, ensure fuel pump is disconnected and ignition is off before testing.
2. Determines if ECM and fuel pump relay circuit are operating correctly. ECM should turn on fuel pump relay. Since engine is not cranking or running, ECM will turn off relay within 2 seconds after ignition is turned on.

Scheme 12

CHART A-5, FUEL PUMP RELAY CIRCUIT (TURBO)

When ignition switch is turned to ON position, ECM activates fuel pump relay to run fuel pump. ECM activates relay as long as it receives ignition reference signals or starter crank signal. If no reference signals are received by ECM within 2 seconds after ignition key is turned on, ECM turns off power to relay.

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

1. This test checks for battery voltage at switching portion of fuel pump relay.
2. This determines if circuit between fuel pump relay (including fuel pump) and ground are okay.
3. This test will check relay circuit for availability of voltage to relay coil.

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

Scheme 13

CHART A-7, FUEL SYSTEM PRESSURE TEST (NON TURBO)

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

1. Use Pressure Gauge (J-34730-1) and Adapter (J-35957-10) . Wrap shop towel around fuel pressure fitting to absorb any fuel leakage when installing gauge. On correctly functioning system, fuel pressure will not leak down when ignition is off.
2. Manifold vacuum pressure is low when engine is idling. When vacuum is applied to fuel pressure regulator diaphragm, fuel pressure will drop to approximately 25-30 psi (1.8-2.1 kg/cm 2 ).
3. Applying vacuum to pressure regulator should cause fuel pressure to drop slightly.
4. Pressure leak-down may be caused by one of following: In-tank fuel pump check valve not holding Pump coupling hose leaking Fuel pressure regulator valve leaking Injector sticking open
5. Pressure less than 35 psi (2.5 kg/cm 2 ) may be caused by one of following: Regulated fuel pressure is too low. System will be running lean and may set Code 44. Hard cold starting and overall poor performance is possible. Restricted flow is causing a pressure drop. Vehicle with fuel pressure drop at idle usually not driveable. Fuel pressure drop while driving will cause engine surge and then stop as pressure rapidly drops.
6. Restricting fuel return line when battery voltage is applied to fuel pump, allows fuel pump to build over regulated pressure. Pressure should be 65 psi (4.5 kg/cm 2 ) or greater.
7. This determines if high fuel pressure is due to restricted fuel line or a pressure regulator problem.

Improper fuel system pressure will contribute to following problems

1. Cranks, but will not run
2. Code 44 or 45
3. Cutting out or "feels" like ignition problem
4. Hesitation, loss of power or fuel economy

Scheme 14

Scheme 15

Scheme 16

CHART A-7, FUEL SYSTEM PRESSURE TEST (TURBO)

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

1. Use Pressure Gauge (J-34730-1) and Adapter (J-35957-10) . Wrap shop towel around fuel pressure fitting to absorb any fuel leakage when installing gauge. On correctly functioning system, fuel pressure will not leak down when ignition is off.
2. Manifold vacuum pressure is low when engine is idling. When vacuum is applied to fuel pressure regulator diaphragm, fuel pressure will drop to approximately 25-30 psi (1.8-2.1 kg/cm 2 ).
3. Applying vacuum to pressure regulator should cause fuel pressure to drop slightly.
4. Pressure leak-down may be caused by one of following: In-tank fuel pump check valve not holding Pump coupling hose leaking Fuel pressure regulator valve leaking Injector sticking open
5. Pressure less than 39 psi (2.7 kg/cm 2 ) may be caused by one of following: Regulated fuel pressure is too low. System will be running lean and may set Code 44. Hard cold starting and overall poor performance is possible. Restricted flow is causing a pressure drop. Vehicle with fuel pressure drop at idle usually not driveable. Fuel pressure drop while driving will cause engine surge and then stop as pressure rapidly drops.
6. Restricting fuel return line when battery voltage is applied to fuel pump, allows fuel pump to build over regulated pressure. Pressure should be 65 psi (4.5 kg/cm 2 ) or greater.
7. This determines if high fuel pressure is due to restricted fuel line or a pressure regulator problem.

Improper fuel system pressure will contribute to following problems

1. Cranks, but will not run
2. Code 44 or 45
3. Cutting out or "feels" like ignition problem
4. Hesitation, loss of power or fuel economy

Scheme 17

Scheme 18

Scheme 19

CHART C-4C, IGNITION SYSTEM CHECK (1.6L NON-TURBO)

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

1. Two spark plug wires are checked to ensure that an open is not present in a wire.
2. A spark indicates problem must be distributor cap or rotor.
3. There should be battery voltage at terminals "A" and "B". Low voltage on both terminals would indicate an open or high resistance circuit from distributor to coil or ignition switch. If terminal "B" voltage was low, but terminal "A" voltage is 10 volts or more, circuit from terminal "B" to ignition coil or ignition coil primary winding is open.
4. Checks for shorted module or grounded circuit from ignition coil to module. Distributor module should be turned off, normal voltage should be about 12 volts. If module is turned on, voltage would be low, but more than 1 volt. This could cause ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through module from battery to TACH terminal.
5. Applying voltage (1.5-8 volts) to module terminal "P" should turn module ON. This will cause TACH terminal (Brown/Red wire) voltage to drop to approximately 7-9 volts. This test determines if module or coil is faulty or if pick-up coil is not generating proper signal to turn module on. This test can be performed by using a DC battery with a rating of 1.5-8 volts. Use of test light is mainly to allow terminal "P" to be probed more easily. Some DVOM's can also be used to trigger module by selecting ohms, usually diode position. In this position the DVOM may have a voltage which can be used to trigger module. Amount of voltage produced by DVOM in ohms position can be checked by another DVOM.
6. This should turn off 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. Module Tester (J-24642) could determine which is at fault.

Scheme 20

Scheme 21

CHART C-4D-3, IGNITION SYSTEM CHECK (IMPULSE 1.6L TURBO)

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

1. Checks to see if spark is present at one or more spark plug wires.
2. Tests for continuity of cam angle sensor.
3. Tests for continuity of cam angle sensor.
4. Voltage will vary in this test depending on cranking speed. Voltage should vary between 500mv at slow cranking speed to 100mv at high cranking speed.

An intermittent may be caused by a poor connection, chaffed wire insulation or broken wire. Inspect cam sensor and DIS module harness connectors for backed out terminals, improper mating, broken locks or broken wire.

Scheme 22

Scheme 23

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.