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发动机不起动时故障诊断
- 检查点火开关。
- 将一个12伏的测试灯的一端连接到点火线圈与转速表之间的接头上，另一端接地。
- 打开点火开关。
- 正常情况下测试灯会亮起。如果测试灯没有亮，说明从点火线圈的初级线圈到电瓶的端极之间有开路。当然对于许多克莱斯勒及福特汽车的点火系统来说，测试灯就不应该亮因为点火线圈的初级线圈就是关闭的。
- 用起动机驱动发动机并观察测试灯。如果测试灯一闪一闪地发光，说明点火系统正常。如果测试灯不亮，说明点火系统有问题。A pick-up is tested with an
ohmmeter. If the pick-up coil is
satisfactory, the module is defective.
Before testing the pick-up, check the
voltage supply to the positive primary
coil terminal with the ignition switch
on before the diagnosis is continued.
- If the test light
flutters, connect a spark plug to the
coil secondary wire, and ground the
spark plug case. The test spark plug
must have the correct voltage
requirement for the ignition system
being tested.
- Crank the engine
and observe the spark plug. If the test
spark plug fires, the ignition coil is
satisfactory. If the test spark plug
does not fire, the coil is probably
defective because the primary circuit
no-start proved the primary circuit is
triggering on and off.
- Connect the test
spark plug to several spark plug wires
and crank the engine while observing the
spark plug. If the test spark plug fired
in step 4 but does not fire at some of
the spark plugs, the secondary voltage
and current is leaking through a
defective distributor cap, rotor, or
spark plug wires, or a plug wire is
open. If the test spark plug fires at
all the spark plugs, the ignition system
is working fine.
- If the cause of the
no-start condition has not yet been
found, check the ignition coil with an
ohmmeter. If the winding resistance
readings are not within specifications,
replace the coil or coil pack. If the
coils are fine, check the primary
circuit for proper voltage.
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Ignition Coil
Resistance
- With the key off
and the battery lead to the ignition
coil disconnected, use an ohmmeter
to measure the primary and secondary
winding resistance of the ignition coil.
When checking the resistance across the
windings, pay particular attention to
the meter reading. If the reading is out
of specifications, even if it is only
slightly out, the coil or coil assembly
should be replaced.
- To check the
primary windings, calibrate an ohmmeter
on the X1 scale and connect the meter
leads to the primary coil terminals to
test the winding.
Ohmmeter connected
to primary coil terminals.
- An infinite
ohmmeter reading indicates an open
winding. The winding is shorted if the
meter reading is below the specified
resistance. Most primary windings have a
resistance of 0.5 to 2 ohms, but the
exact manufacturer's specifications must
be compared to the meter readings.
- To check the
secondary winding, calibrate the meter
on the X1,000 scale and connect it from
the coil's secondary terminal to one of
the primary terminals.
Ohmmeter connected
from one primary terminal to the coil tower
to test secondary winding.
- A meter reading
below the specified resistance indicates
a shorted secondary winding. An infinite
meter reading proves that the winding is
open.
- In some coils, the
secondary winding is connected from the
secondary terminal to the coil frame.
When the secondary winding is tested in
these coils, the ohmmeter must be
connected from the secondary coil
terminal to the coil frame or to the
ground wire terminal extending from the
coil frame. Many secondary windings have
8,000 to 20,000 ohms resistance, but the
meter readings must be compared to the
manufacturer's specifications. The
ohmmeter tests do not indicate such
defects as defective insulation around
the coil windings, which causes
high-voltage leaks. Therefore, an
accurate indication of coil condition is
the coil maximum voltage output test
with a test spark plug connected from
the coil secondary wire to ground as
explained in the no-start diagnosis.
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