Engine Controls - Tests W/o Codes - Carbureted Isuzu Amigo I

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in F - CARB BASIC TESTING and G - CARB TESTS W/ CODES articles in the ENGINE PERFORMANCE Section. Use this article to diagnose driveability problems existing when a hard fault code is not present.

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, a system test or an adjustment.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

Note. For specific testing procedures, see I - CARB SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. For specifications, see D - CARB ADJUSTMENTS or SPECIFICATIONS articles in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in F - CARB BASIC TESTING and G - CARB TESTS W/ CODES articles in the ENGINE PERFORMANCE Section were performed before diagnosing a symptom. Symptoms available for diagnosis include

1. Visual Check
2. No Start - Engine Cranks Okay
3. No Start - Engine Cranks & Spark Occurs
4. Hard Start - Cold
5. Hard Start - Hot
6. Stall After Start - Cold
7. Stall After Start - Hot
8. Hesitation, Sag, Stumble
9. Surges And/Or Chuggle
10. Lacks Power, Sluggish
11. Backfire
12. Misses
13. Cuts Out
14. Rough, Unstable Idle, Stalling
15. Won't Idle
16. Poor Fuel Economy
17. Dieseling, Run-On
18. Detonation/Spark Knock
19. Excessive Exhaust Emissions

VISUAL CHECK

1. Inspect vacuum hoses for splits, kinks and proper connection. For vacuum hose routing, see VACUUM DIAGRAMS article.
2. Ensure ignition wires do not show signs of cracking, hardness or carbon tracking. Ensure proper ignition wire routing and firing order.
3. Ensure wiring is connected properly, and not pinched or cut.

NO START - ENGINE CRANKS OKAY

1. Check distributor rotor.
2. Check high tension cable.
3. Check main relay or ECM relay.
4. Check ignition coil.
5. Ensure ignition timing is correct.
6. Check spark plugs.
7. Check valve timing.
8. Inspect distributor cap for moisture, cracks, dust, burns or carbon tracking. Ensure distributor drive pin is not broken by trying to move distributor shaft by hand.
9. Ensure fuel is in carburetor by operating accelerator pump. If gas is not present, check fuel tank, fuel filter and fuel pump.
10. Ensure crankcase oil is not fuel contaminated. If fuel is present, check fuel pump for a ruptured diaphragm. Ensure carburetor is not flooding.

NO START - ENGINE CRANKS & SPARK OCCURS

1. Check fuel quantity.
2. Check for contaminated fuel.
3. Check for clogged fuel filter and fuel lines.
4. Check fuel pump.
5. Check carburetor choke.
6. Check evaporative emission control system.
7. Ensure crankcase oil is not contaminated with fuel. If fuel is present, check fuel pump for a ruptured diaphragm. Ensure carburetor is not flooding.

HARD START - COLD

1. Check carburetor choke, vacuum break(s), linkage and unloader operation.
2. Check distributor for worn shaft. Check pick-up coil for bare or shorted wires. Ensure pickup coil resistance and connections are correct.
3. Check EGR system.
4. Ensure driver is using correct starting procedure.
5. Ensure carburetor is not flooding.
6. Ensure fuel filter is not clogged.
7. Ensure spark plugs are okay.
8. Ensure ignition timing is correct.
9. Verify distributor cap is free of moisture.

HARD START - HOT

1. Check distributor for worn shaft. Check pick-up coil for bare or shorted wires. Ensure pick-up coil resistance and connections are correct.
2. Check carburetor choke and ensure it is not closed.
3. Check for obvious overheating problems.
4. Check EGR system.
5. Ensure driver is using correct starting procedure.
6. Ensure carburetor is not flooding.
7. Ensure fuel filter is not clogged.
8. Ensure Early Fuel Evaporative (EFE) heater is off.
9. Ensure spark plugs are okay.
10. Ensure ignition timing is correct.
11. Verify distributor cap is free of moisture.

STALL AFTER START - COLD

1. Check thermostatic air cleaner operation. Ensure hot air tube is connected to air cleaner.
2. Check carburetor choke, vacuum break(s), linkage and unloader operation.
3. Check vacuum break linkage for movement, while removing and installing vacuum hoses. If linkage does not move, ensure linkage is not binding. If linkage is okay, use vacuum pump to check vacuum break.
4. Check accelerator pump operation.
5. Check EGR system.
6. Ensure fast idle speed and idle speed are set correctly.
7. Ensure Early Fuel Evaporative (EFE) heater is on.
8. Ensure ignition timing is correct.
9. Ensure gasoline quality (not poor or contaminated).

STALL AFTER START - HOT

1. Check thermostatic air cleaner operation.
2. Check carburetor choke, vacuum break(s), linkage and unloader operation.
3. Check accelerator pump operation.
4. Check for obvious overheating problems. Ensure cooling fan is operating.
5. Check EGR system.
6. Ensure ignition timing is correct.
7. Ensure gasoline quality (not poor or contaminated).
8. Ensure carburetor is not flooding.
9. Ensure fast idle speed and idle speed are correct.

HESITATION, SAG, STUMBLE

1. Check thermostatic air cleaner operation.
2. Check carburetor choke, vacuum break(s), linkage and unloader operation.
3. Check accelerator pump operation.
4. Check throttle position sensor adjustment.
5. Check EGR system.
6. Ensure ignition timing is correct.
7. Ensure gasoline quality (not poor or contaminated).
8. Ensure carburetor is not flooding.

SURGES AND/OR CHUGGLE

1. Check thermostatic air cleaner operation.
2. Check carburetor choke, vacuum break(s), linkage and unloader operation.
3. Check accelerator pump operation.
4. Check for arcing to coil attaching screws inside distributor cap.
5. Check fuel pump.
6. Check EGR system.
7. Ensure fuel filter is not clogged.
8. Ensure carburetor is not flooding.
9. Ensure spark plugs are okay.
10. Ensure ignition timing is correct.
11. Ensure gasoline quality (not poor or contaminated).

LACKS POWER, SLUGGISH

1. Check thermostatic air cleaner operation.
2. Check accelerator pump operation.
3. Ensure ignition timing is correct.
4. Ensure fuel filter is not clogged.
5. Ensure air filter is clean.
6. Ensure transmission kickdown works properly.
7. Ensure spark plugs are okay.
8. Ensure exhaust system is not restricted.
9. Ensure carburetor is not flooding.
10. Ensure valve timing and compression are correct. Ensure camshaft is not worn.
11. Ensure gasoline quality (not poor or contaminated).
12. Verify throttle valve opens completely.

BACKFIRE

1. Check thermostatic air cleaner operation.
2. Check accelerator pump operation.
3. Check carburetor choke, vacuum break(s), linkage and unloader operation.
4. Check air injection system control valves.
5. Check for crossed plug wires. Check for cross-firing inside distributor cap due to carbon tracking.
6. Check for intermittent failure of pick-up coil or ignition primary connections.
7. Check EGR system.
8. Ensure compression is correct. Check for sticking or leaky valves.
9. Ensure exhaust system is not restricted.
10. Ensure valve timing is correct.

MISSES

1. Check for camshaft lobe or rocker arm wear, or broken valve springs.
2. Check EGR system.
3. Ensure ignition wires are routed properly.
4. Ensure secondary ignition system is working properly.
5. Ensure distributor cap is free of moisture, dust, cracks and carbon tracking.
6. Ensure ignition coil is grounded properly.
7. Ensure spark plugs are okay.

CUTS OUT

1. Check for camshaft lobe or rocker arm wear, or broken valve springs.
2. Ensure secondary ignition system is working properly.
3. Ensure spark plugs are okay.
4. Ensure pick-up coil is working properly. Check pick-up coil resistance and connections at module.
5. Ensure exhaust system is not restricted.

ROUGH, UNSTABLE IDLE, STALLING

1. Check carburetor for flooding and correct idle speed.
2. Check EGR system.
3. Ensure gasoline quality (not poor or contaminated).
4. Ensure throttle linkage is not sticking or binding.

If rough idle occurs when engine is hot, perform the following checks

1. Check PCV system operation.
2. Check fuel evaporative system.
3. Ensure spark plug gap is correct.
4. Ensure compression is correct.
5. Ensure ignition timing is correct.
6. Ensure exhaust system is not restricted.

WON'T IDLE

1. Check carburetor for flooding and correct idle speed.
2. Check EGR system.
3. Ensure gasoline quality (not poor or contaminated).
4. Ensure spark plug gap is correct.
5. Ensure exhaust system is not restricted.

POOR FUEL ECONOMY

1. Check for brake drag or clutch slip.
2. Check thermostatic air cleaner operation.
3. Check speedometer for proper calibration.
4. Ensure primary and secondary ignition systems are working correctly.
5. Ensure ignition timing is correct.
6. Ensure compression is within specification.
7. Ensure exhaust system is not restricted.
8. Poor fuel quality.
9. Test drive vehicle with customer and observe his driving habits.

DIESELING, RUN-ON

1. Check carburetor choke, vacuum break(s), linkage and unloader operation.
2. Check for carbon build-up inside combustion chamber.
3. Check for overheating.
4. Check fuel-cut (slow-cut) solenoids.
5. Ensure idle speed and ignition timing are correct.

DETONATION/SPARK KNOCK

1. Check for overheating.
2. Check for vacuum leaks at carburetor mounting and intake manifold.
3. Ensure gasoline quality (not poor or contaminated).
4. Check throttle position sensor operation.
5. Check for carbon build-up inside combustion chamber.
6. Check spark plug heat range.
7. Check EGR system.
8. Ensure ignition timing is correct.
9. Ensure distributor advance weights and springs are not sticking.
10. Carbon deposits in combustion chambers.
11. Improper transmission gear selection.

EXCESSIVE EXHAUST EMISSIONS

1. Check carburetor choke, vacuum break(s), linkage and unloader operation.
2. Check fast idle adjustment.
3. Check PCV system operation.
4. Check catalytic converter for lead contamination. Check for fillpipe restrictor tampering.
5. Check air injection system.
6. Check carburetor for flooding.
7. Check fuel evaporative canister for loading. Check canister purge system operation.
8. Ensure air cleaner is clean.
9. Ensure idle speed and air/fuel mixture are correct.
10. Ensure ignition timing is correct.
11. Check for vacuum leaks.
12. Check thermostatic air cleaner operation.
13. Check cooling system and cooling fan operation.
14. Check for carbon build-up in combustion chamber.
15. Check ignition timing for excessive base advance.
16. Check fuel-cut system.
17. Check EGR system.

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the computer setting a fault code which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM, while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.

Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.

Intermittent Simulation

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component.
2. Heat component.
3. Wiggle or bend wiring harness.
4. Spray component with water.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

INTERMITTENT CHECK ENGINE LIGHT

1. Inspect CHECK ENGINE light wire to ECM.
2. Check ALDL connector wire to ECM for short to ground.
3. Check for electrical system interference caused by defective relay, ECM-driven solenoid or switch. These can cause voltage spikes. Normally, spikes occur when faulty component is activated.
4. Check for improper installation of electrical options, such as stereos, car phones and fog lights.
5. Ensure CHECK ENGINE light comes on, but does not stay on.
6. Connect a voltmeter to a suspected circuit and ground. If voltage reading changes as CHECK ENGINE light comes on, the problem is located in that circuit.