2000 YAMAHA YZ426F oil

6 - 2
–+ELEC

MAP-CONTROLLED CDI UNIT
MAP-CONTROLLED CDI UNIT
A map-controlled, CDI ignition system is used in the YZ426F.
The microcomputer in the CDI unit detects the engine speed and throttle position, thus determining
the optimum ignition timing through the entire operating range. In this way, quick throttle response
can be achieved according to various riding conditions.
CDI unit
Throttle position sensor
Pickup coil AC magneto rotorIgnition coil

n
Function of Component

Component Function
TPS
(throttle position sensor)Detects throttle valve opening and inputs it into the computer in the
CDI unit as a throttle opening signal.
Pickup coil Detects signal rotor revolutions and inputs them into the computer in
the CDI unit as engine revolution signals.
CDI unit The signals of the TPS and pickup coil sensor are analyzed by the
computer in the CDI unit, which then adjusts ignition timing for the
operation requirements.
n
Principal of 3-Dimensional Control
Conventionally, ignition timing was controlled only
by engine revolutions (2-dimensional control).
However, ignition timing needs advancement also
by engine load. Thus, accurate ignition timing can
be determined by adding throttle opening to deter-
mine ignition timing (3-dimensional control).
Revolutions
Ignition timing
Throttle opening

3-D Image Map of Ignition Timing
(different from actual characteristics)

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–+ELEC

IGNITION SYSTEM
EC620000
IGNITION SYSTEM
EC621001
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
NOTE:

l
Remove the following parts before inspection.
1) Seat
2) Fuel tank
l
Use the following special tools in this inspection.
Spark gap test*Clean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check “ENGINE STOP”
button.Replace.
Check ignition coil. Primary coil Replace.
Secondary coilReplace.
Check CDI magneto. Pick-up coil Replace.
Source coil Replace.
Check neutral switch. Repair or replace.
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-03112/90890-03112
No Spark
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good
No good
OK

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–+ELEC

IGNITION SYSTEM
EC626002
IGNITION COIL INSPECTION
1. Inspect:
l
Primary coil resistance
Out of specification
®
Replace.
Tester (+) lead
®
Orange lead
1

Tester (–) lead
®
Black lead
2

Primary coil
resistanceTester selector
position
0.20 ~ 0.30
W
at
20 ˚C (68 ˚F)
W

´
1
2. Inspect:
l
Secondary coil resistance
Out of specification
®
Replace.
NOTE:

When inspecting the secondary coil resis-
tance, remove the spark plug cap.
EC627011
CDI MAGNETO INSPECTION
1. Inspect:
lPick-up coil resistance
Out of specification ® Replace. Tester (+) lead ® Spark plug lead 1
Tester (–) lead ® Orange lead 2
Secondary coil
resistanceTester selector
position
9.5 ~ 14.3 kW at
20 ˚C (68 ˚F)kW ´ 1
Tester (+) lead ® Red lead 1
Tester (–) lead ® White lead 2
Pick-up coil
resistanceTester selector
position
248 ~ 372 W at
20 ˚C (68 ˚F)W ´ 100

6 - 6
–+ELECIGNITION SYSTEM
2. Inspect:
lSource coil 1 resistance
Out of specification ® Replace.
3. Inspect:
lSource coil 2 resistance
Out of specification ® Replace. Tester (+) lead ® Brown lead 1
Tester (–) lead ® Green lead 2
Source coil 1
resistanceTester selector
position
720 ~ 1,080 W
at 20 ˚C (68 ˚F)W ´ 100
Tester (+) lead ® Pink lead 1
Tester (–) lead ® Black lead 2
Source coil 2
resistanceTester selector
position
44 ~ 66 W at
20 ˚C (68 ˚F)W ´ 10
NEUTRAL SWITCH INSPECTION
1. Inspect:
lNeutral switch conduct
No continuity while in neutral ® Replace.
Continuity while in gear ® Replace.
EC628000
CDI UNIT INSPECTION
Check all electrical components. If no fault is
found, replace the CDI unit. Then check the
electrical components again.Tester (+) lead ® Sky blue lead 1
Tester (–) lead ® Ground
Sb
1GroundTester selec-
tor position
NEUTRALW ´ 1INGEAR
–+ W´1
1
R/W
W Sb L/W

6 - 7
–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
EC69000
TPS (THROTTLE POSITION SENSOR) SYSTEM
EC691000
INSPECTION STEPS
If the TPS will not operate, use the following inspection steps.
*marked: Refer to “IGNITION SYSTEM” section.
NOTE:
lRemove the following parts before inspection.
1) Seat
2) Fuel tank
lUse the following special tools in this inspection.
Check entire ignition
system for connection.Repair or replace.
Check TPS. TPS coil Replace.
*Check CDI magneto. Source coil Replace.
Check CDI unit.TPS input
voltageReplace.
Pocket tester:
YU-03112/90890-03112Inductive tachometer:
YU-8036-1
Engine tachometer:
90890-03113
No good
No good
No good
No good
OK
OK
OK

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–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
EC624000
COUPLERS AND LEADS CONNECTION
INSPECTION
1. Check:
lCouplers and leads connection
Rust/dust/looseness/short-circuit ®
Repair or replace.
TPS COIL INSPECTION
1. Inspect:
lTPS coil resistance
Out of specification ® Replace.
2. Loosen:
lThrottle stop screw
NOTE:
Turn out the throttle stop screw until the throt-
tle shaft is in the full close position.Tester (+) lead ® Blue lead 1
Tester (–) lead ® Black lead 2
TPS coil
resistanceTester selector
position
4 ~ 6 kW at
20 ˚C (68 ˚F)kW ´ 1
3. Inspect:
lTPS coil variable resistance
Check that the resistance in increased
as the throttle grip is moved from the
full close position to the full open posi-
tion.
Out of specification ® Replace.
Tester (+) lead ® Yellow lead 1
Tester (–) lead ® Black lead 2
TPS coil variable
resistanceTester selec-
tor position
Full closedFull opened
kW ´ 1 0 ~ 2 kW at
20 ˚C
(68 ˚F)4 ~ 6 kW at
20 ˚C
(68 ˚F)

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–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
TPS REPLACEMENT AND ADJUSTMENT
1. Remove:
lTPS coupler
lScrew (TPS) 1
lPlain washer 2
lTPS 3
2. Replace:
lTPS
3. Install:
lTPS 1
lPlain washer 2
lScrew (TPS) 3
lTPS coupler
NOTE:
lAlign the slot a in the TPS with the projec-
tion b on the carburetor.
lTemporarily tighten the screws (TPS).
4. Adjust:
lIdle speed
Refer to “IDLE SPEED ADJUSTMENT”
section in the CHAPTER 3.
5. Calculate:
lTPS coil resistance at idle speed.

If the TPS coil resistance is 5 kW, then the TPS
coil resistance at idle speed is:
5 kW ´ (0.13 ~ 0.15) = 650 ~ 750 W
Refer to “TPS COIL INSPECTION” sec-
tion about the TPS coil resistance. TPS coil resistance at idle speed:
TPS coil resistance ´ (0.13 ~ 0.15)

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–+ELECTPS (THROTTLE POSITION SENSOR) SYSTEM
6. Adjust:
lTPS coil resistance at idle speed
Adjustment steps:
Adjust the angle of the TPS 1 to obtain
the resistance calculated (example: 650 ~
750 W)
Tester (+) lead ® Yellow lead 2
Tester (–) lead ® Black lead 3
7. Tighten:
lScrew (TPS) 1
8. Install:
lTPS coupler
EC694000
TPS INPUT VOLTAGE INSPECTION
1. Disconnect the TPS coupler.
2. Start the engine.
3. Inspect:
lTPS input voltage
Out of specification ® Replace the CDI
unit.
Tester (+) lead ® Blue lead 1
Tester (–) lead ® Black lead 2
TPS input
voltageTester selector
position
4 ~ 6 V DCV-20