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Troubleshooting the DFI System
Startability:
(A): The starter motor rotates the engine but there is no combustion
and the engine doesn’t start.
(B): There is combustion, but the engine stops immediately.
•You need to push the starter button long to start the engine.
When the engine is cold, this problem may be caused by
too lean fuel-air mixture (due to poor fuel supply, ISC valve
malfunction, water or air temperature sensor short, pressure
regulator malfunction, leak from oil filler cap, crankcase breather
hose or air cleaner drain hose).
When the engine is hot, the problem may be caused by too
rich fuel-air mixture (due to valve leak of the injectors, water
or air temperature sensor disconnection or pressure regulator
malfunction).
When the engine is hot or cold, the problem may be caused by
too lean fuel-air mixture (due to fuel pump malfunction or poor
wiring connection).
Idling stability:
(C): Unstable idling (rough idling) (may be caused by richer or leaner
fuel-air mixture)
•The idle speed fluctuates. Richer or mixture can be identified
by subdued engine sound, black smoke or smell of gasoline, and
leaner mixture by rattling sound.
(D): Incorrect idle speed (may be caused by richer or leaner fuel-air
mixture)
•The idle speed cannot be adjusted within the specified range.
(E): Lack of idling consistency (may be caused by richer or leaner
fuel-air mixture)
•The engine cannot maintain idling. The following two symptoms
may be found.
The engine stops when closing the throttle.
! ISC valves are suspect.
The engine stops when opening the throttle.
! The throttle sensor is suspect.
Driveability:
(F): Hesitation (instantaneous delay of acceleration, may be caused
by clogged fuel line, instantaneous change to leaner fuel-air
mixture, and delay of ignition timing)
Too lean fuel-air mixture is due to too low fuel pressure, throttle
sensor malfunction, loose injector connectors. The other causes
are shortage or disconnection of pickup coil or ignition coil
primary lead, and loose terminal of battery (-) lead or engine
ground lead.
Hesitation [A]
Severe Hesitation
Normal [C]
Beginning [D] of Opening the Throttle
Throttle Opening [E]
Motorcycle Speed [F]
(G): Poor acceleration
The motorcycle runs smoothly, but cannot accelerate in response
to throttle opening. If the motorcycle cannot reach maximum
speed, the fuel filter may be clogged.
3-40 FUEL SYSTEM (DFI)
Troubleshooting the DFI System
(H): Stumble (due to temporal power drop probably caused by too
lean fuel-air mixture.)
When the motorcycle is about to accelerate, the engine speed
cannot increase in response to throttle opening, and increases
with a lag (longer lag than in hesitation) at opening [C] the
throttle.
Stumble [A]
Normal [D]
Idling [E]
Opening the throttle [F]
Motorcycle Speed [G]
(I): Surge (may be caused unstable fuel supply)
A forward and backward, periodic slight movement of a motorcycle
at acceleration, deceleration, or at cruising may be caused
by torsional vibration of the final drive due to unstable combustion
in the cylinder head.
(J): Knock (often caused by leaner fuel-air mixture)
A periodic, rattling, thumping or pounding noise caused by
spontaneous ignition of the air-fuel mixture in an overheated
cylinder head, leading to engine damage. Knocking can also be
caused by a worn connecting rod bearing, uneven combustion
too high cylinder compression, or incorrect fuel.
(K): Backfire (may be caused by leaner fuel-air mixture)
An explosion of unburned or partially burned fuel in an inlet pipe
due to incomplete combustion in the cylinder head, wrong engine
valve timing, vacuum switch broken or air suction valve trouble,
mainly during decelerating.
(L): After fire (may be caused by richer fuel-air mixture)
An explosion of gases accumulated in a muffler caused by
incomplete combustion in the cylinder head, wrong plug gap or
burned electrode. Also it is caused by delayed ignition during
starting or during decelerating, resulting in an explosion after
the end of the combustion (rich fuel-air mixture is due to high
fuel pressure, water temperature sensor or its lead or ground
lead open).
Engine doesn’t stop (M):
(N): Run-on (dieseling, caused by engine overheating)
Continuous running of an engine with the ignition SW OFF.
Others:
Sometimes the DFI system may repeat a fault and its recovery by
itself. This could be caused by intermittence of loose connectors
or fraying leads.
Opening (disconnection) of the water or inlet air temperature
and its wiring makes fuel-air mixture richer. Conversely, short
of these parts makes the mixture leaner.
Too high fuel pressure makes fuel-air mixture richer.
If the fuel pump operates intermittently and if the DFI fuse
sometimes blows, the pump bearings could have worn.
Does this bring anything to mind?