Symptoms or possible Causes

Actions (chapter)

Cylinder, piston worn

Inspect and replace (see chapter 5).

Piston ring bad (worn, weak, broken or sticking)

Inspect and replace (see chapter 5).

Piston ring/groove clearance excessive

Inspect and replace (see chapter 5).

Cylinder head gasket damaged

Replace (see chapter 5).

Cylinder head warped

Inspect and replace (see chapter 5).

No valve clearance

Adjust (see chapter 2).

Valve guide worn

Inspect and replace (see chapter 5).

Valve spring broken or weak

Inspect and replace (see chapter 5).

Valve not seating properly (valve bent, worn or

Inspect and repair or replace (see chapter 5).

carbon accumulating on seating surface)

Symptoms or Possible Causes

Actions (chapter)

Spark weak :

Battery voltage low

Inspect and charge (see chapter 16).

Spark plug dirty, broken or gap maladjusted

Clean spark plugs and adjust plug gap (see

chapter 2).

Spark plug cap trouble

Inspect the stick coil (see chapter 16).

Spark plug cap shorted or not in good contact

Reinstall or inspect stick coil (see chapter 16).

Spark plug incorrect

Replace it with the correct plug (see chapter 16).

IC igniter in ECU trouble

Inspect (see chapter 16).

Crankshaft sensor trouble

Inspect (see chapter 16).

Stick coil trouble

Inspect (see chapter 16).

Fuel/air mixture incorrect :

Little fuel in tank

Supply fuel (see Owner’s Manual).

Air cleaner clogged, poorly sealed, or missing

Clean element or inspect sealing (see chapter 3).

Air cleaner duct loose

Reinstall (see chapter 3).

Air cleaner O-ring damaged

Replace (see chapter 3).

Fuel tank air vent obstructed

Inspect and repair (see chapter 3).

Throttle body assy loose

Reinstall (see chapter 3).

Throttle body assy O-ring damage

Replace (see chapter 3).

Choke lever pulled

Push it (see chapter 3).

Fuel filer or pump screen clogged

Inspect and replace fuel pump (see chapter 3).

Fuel pressure regulator clogged

Inspect fuel pressure and replace fuel pump (see

chapter 3).

Fuel line clogged

Inspect and repair (see chapter 3).

Inlet air pressure sensor trouble

Inspect (see chapter 3).

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Thermostat trouble

Inspect and replace (see chapter 4).

Unstable (rough) idling :

Fuel injector trouble

Inspect (see chapter 3).

Main throttle sensor trouble

Inspect (see chapter 3).

Crankshaft sensor trouble

Inspect (see chapter 3).

Throttle valves not synchronizing

Inspect (see chapter 2).

FUEL SYSTEM (DFI) 3-27

DFI System Troubleshooting Guide

Symptoms or Possible Causes

Actions (chapter)

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Atmospheric pressure sensor trouble

Inspect (see chapter 3).

Fuel pressure too low or too high

Inspect (see chapter 3).

Battery voltage low

Inspect and charge (see chapter 16).

Incorrect idle speed :

Water temperature sensor trouble

Inspect (see chapter 3).

Main throttle sensor trouble

Inspect (see chapter 3).

Engine stalls easily :

Fuel pump trouble

Inspect (see chapter 3).

Fuel injector trouble

Inspect (see chapter 3).

Main throttle sensor trouble

Inspect (see chapter 3).

Camshaft position sensor trouble

Inspect (see chapter 3).

Fuel pressure too low or too high

Inspect (see chapter 3).

Inlet air pressure sensor trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Fuel line clogged

Inspect and repair (see chapter 3).

Fuel pressure too low or too high

Inspect (see chapter 3).

Fuel pressure regulator trouble

Inspect fuel pressure and replace fuel pump (see

chapter 3).

Crankshaft sensor trouble

Inspect (see chapter 16).

Stick coil trouble

Inspect (see chapter 16).

Compression Low :

Spark plug loose

Reinstall (see chapter 16).

Cylinder head not sufficiently tightened down

Tighten (see chapter 5).

No valve clearance

Adjust (see chapter 2).

Cylinder, piston worn

Inspect and replace (see chapter 5).

Piston ring bad (worn, weak, broken or sticking)

Inspect and replace (see chapter 5).

Piston ring/groove clearance excessive

Inspect and replace (see chapter 5).

Cylinder head gasket damaged

Replace (see chapter 5).

Cylinder head warped

Inspect and replace (see chapter 5).

Valve guide worn or stem seal damaged

Inspect and replace (see chapter 5).

Valve spring broken or weak

Inspect and replace (see chapter 5).

Valve not seating properly (valve bent, worn or

Inspect and repair or replace (see chapter 5).

carbon accumulating on seating surface)

Camshaft cam worn

Inspect and replace (see chapter 5).

Hesitation :

Too low fuel pressure

Inspect (see chapter 3).

Clogged fuel line

Inspect and repair (see chapter 3).

Cracked or obstructed inlet air pressure sensor

Inspect and repair or replace (see chapter 3).

hose

Fuel pump trouble

Inspect (see chapter 3).

Fuel injector trouble

Inspect (see chapter 3).

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Symptoms or Possible Causes

Actions (chapter)

Main throttle sensor trouble

Inspect (see chapter 3).

Subthrottle sensor trouble

Inspect (see chapter 3).

Subthrottle valve actuator trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Atmospheric pressure sensor trouble

Inspect (see chapter 3).

Inlet air pressure sensor trouble

Inspect (see chapter 3).

Loose injector connectors

Remedy (see chapter 3).

Crankshaft sensor trouble

Inspect and repair or replace (see chapter 16).

Stick coil trouble

Inspect and repair or replace (see chapter 16).

Loose terminal of battery (–) lead or engine

Inspect and repair (see chapter 16).

ground lead

Delay of ignition timing

Inspect crankshaft sensor and IC igniter in ECU

(see chapter 16).

Poor acceleration :

Choke lever pulled

Push it (see chapter 3).

Too low fuel pressure

Inspect (see chapter 3).

Water or foreign matter in fuel

Change fuel. Inspect and clean fuel system (see

chapter 3).

Clogged fuel filter or pump screen

Inspect and replace fuel pump (see chapter 3).

Fuel pump trouble

Inspect (see chapter 3).

Fuel injector trouble

Inspect (see chapter 3).

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Atmospheric pressure sensor trouble

Inspect (see chapter 3).

Subthrottle sensor trouble

Inspect (see chapter 3).

Subthrottle valve actuator trouble

Inspect (see chapter 3).

Stick coil trouble

Inspect and replace (see chapter 16).

Engine oil level to high

Repair (see chapter 7).

Spark plug dirty, broken or gap maladjusted

Clean spark plugs and adjust plug gap (see

chapter 2).

Stumble :

Too low fuel pressure

Inspect (see chapter 3).

Fuel injector trouble

Inspect (see chapter 3).

Main throttle sensor malfunction

Inspect (see chapter 3).

Subthrottle sensor trouble

Inspect (see chapter 3).

Subthrottle valve actuator trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Inlet air pressure sensor trouble

Inspect (see chapter 3).

Surge :

Fuel pressure regulator trouble (Inspect and

Unstable fuel pressure

replace fuel pump) or kinked fuel line (Inspect and

repair fuel line) (see chapter 3).

Fuel injector trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Backfiring when deceleration :

FUEL SYSTEM (DFI) 3-29

DFI System Troubleshooting Guide

Symptoms or Possible Causes

Actions (chapter)

Spark plug dirty, broken or gap maladjusted

Clean spark plugs and adjust plug gap (see

chapter 2).

Too low fuel pressure

Inspect (see chapter 3).

Fuel pump trouble

Inspect (see chapter 3).

Main throttle sensor trouble

Inspect (see chapter 3).

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Atmospheric pressure sensor trouble

Inspect (see chapter 3).

Inlet air pressure sensor trouble

Inspect (see chapter 3).

Vacuum switch valve broken

Inspect and replace (see chapter 5).

Air suction valve trouble

Inspect and replace (see chapter 5).

After fire :

Crankshaft sensor trouble

Inspect (see chapter 16).

Spark plug burned or gap maladjusted

Adjust plug gap or replace plug (see chapter 2).

Inlet air temperature sensor trouble

Inspect (see chapter 3).

Water temperature sensor trouble

Inspect (see chapter 3).

Atmospheric pressure sensor trouble

Inspect (see chapter 3).

Inlet air pressure sensor trouble

Inspect (see chapter 3).

Fuel injector trouble

Inspect (see chapter 3).

Run-on (dieseling) :

Ignition switch trouble

Inspect and replace (see chapter 16).

Engine stop switch trouble

Inspect and repair or replace (see chapter 16).

Fuel injector trouble

Inspect (see chapter 3).

Loose terminal of battery (–) lead or ECU

Inspect and repair (see chapter 16).

ground lead

Carbon accumulating on valve seating surface

Repair (see chapter 5).

Engine overheating

(see Overheating of Troubleshooting Guide, see

chapter 17)

Other :

Engine oil viscosity too high

Change (see chapter 2).

Drive train trouble

Inspect drive chain (see chapter 2) and sprocket

(see chapter 11).

Brake dragging

Inspect caliper fluid seal damage or clogging

of master cylinder relief and supply ports (see

chapter 12).

Clutch slipping

Inspect friction plates for wear (see chapter 6).

Engine overheating

(see Overheating of Troubleshooting Guide, see

chapter 17)

Vacuum switch valve trouble

Inspect and replace (see chapter 5).

Air suction valve trouble

Inspect and replace (see chapter 5).

Check that DFI connectors are clean and tight,

Intermittent any DFI fault and its recovery

and examine wires for signs of burning or fraying

(see chapter 3).