198
gear as it rotates. The sensor sends the resulting electrical
signal to the tachometer, which converts it into indicator
needle movement.
NOTE
While the sensors
for
all
engines are inter-
changeable
. the tachometers are not.
Due
to
the difference in
number
of
ring
gear
teeth.
the tachometer used on 3N..., and 3HM35
engines
is nol interchangeable with other
engines.
Before troubleshooting the tachometer,check for faulty
connections, then recheck tachometer operation. If the
problem remains. refer to the follow ing sections.
CHAPTE R NINE
Tachometer S
ender
To check the tachometer sender, proceed as follows:
1. Disconnect the leads from the sender (Figure 29).
2. With the
engine stopped. use an ohmmeter to check the
resistance between the sender leoninaIs. Resistance
should be 1500-1700 ohms.
3. Run the engine. Measure the alternating
current volt-
age between the sender terminals. The voltage reading
should be at least one volt.
4. If the sender fails either test, replace the sender.
Tachometer Ga uge
To check the tachometer gauge unit, proceed as fol-
lows:
I. Disconnect the rcd'bleck and black wire leads from the
tachometer. With the key switch ON, measure the voltage
between the two wires. There should be 10-16 volts (bat-
tery voltage).
If
not, determine the cause.
2. Disconnect the orange and blue/red
wire leads from
the tachometer. Run the engine. Measure the alternating
current voltage between the orange and blue/red wire
leads. The voltage reading should be at least one volt.
3. If the voltage reading in Step 2 is
less than one volt,
check the wires and connections and check the sender as
described in the preceding section.
..t.
If the voltage readings in Steps I and 2 are satisfactory,
replace the tachometer.
Mo
de
l
lGM
,lGM10
2GM
,2GM20
3GM, 3GM30, 3HM
3HM35
Table
1
BATTERY
CAPACITY
(MINIMUMI
Volt
ag
e
12V
12V
12 V
12 V
B
attery
capacity
70 am
p-ho
urs
70 am
p-ho
urs
70
amp-ho
urs
100 amp-hours
T
abl
e 2
ALTERNATOR
AND
STARTER
MOTOR
TIGHTENING
TORQUES
Mod
e l
lGM
,
lGM10
,
2GM
.2GM20
,
3GM
,3GM30
3HM
,3
HM35
Alternato
r
mountin
g
bolt
22-27 Nom
(16-20 ft.- lb.)
22-27
N
.m
(16-20 ft .-lb.)
Start
er
moto
r
mounting
bolts
45-50 Nom
(33-37 ft .-Ib,)
75-80
Nom
(55-59 ft.- lb.)
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