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Electrical: Engine Starting, Charging
"Zero engagement" or "no-clicking" activation of the starter solenoid. This can
be caused by an unintentional activation of a vehicle anti-theft system. In
other cases, a defective ignition switch,
harness/loose wiring connection can cause the problem. The most accurate
way to test these components is to connect a DVOM to the primary wire
connection on the starter solenoid. Using the min./max. feature found on most
professional DVOMs or multimeters, record the voltage at the solenoid terminal
when turning the ignition switch to the "crank" position. If battery voltage is
recorded, the above components should be considered in good condition. If the
starter clicks, but doesn't engage, the problem is usually caused by a faulty
starter solenoid that's not engaging the starter drive gear. In most cases,
replacing starter solenoids is not a cost-effective procedure compared to
replacing the defective starter with a remanufactured unit.
Starter motor is running but fails to engage the flywheel ring gear or when the
engagement is rough and noisy. In most of these cases, the overrun or one-
way roller clutch on the starter drive gear is worn or sticking. In the remainder
of these cases, the flywheel ring gear itself is either worn, or has broken or
missing teeth.
Low-cranking speed issue caused by worn shaft bushings. The starter's
amperage draw will be unusually high for the application. Also, when starter
current draw is high, remember that battery voltage will often drop below 9.6
volts. This is enough to affect system electronics, which, in turn, will affect
fuel pump operation. Engines must crank at about 200-300 rpm to activate
the electronic fuel injection. When the ECU "sees" a strong, sustained signal
from the crankshaft position sensor, it will activate the fuel pump relay in
order to pressurize the fuel injectors. Without a reliable RPM signal indicating
sufficient cranking speed, the ECU may not activate the fuel pump relay,
thereby creating a cranking, no-start condition.
Keep in mind that simply dropping a permanent magnet starter can fracture a
field magnet, which may cause a variety of cranking speed symptoms.
Troubleshooting the Starter
In the Shop:
To accurately test a starter, you need a test stand that can measure amp load,
voltage and rpm. A good starter will normally draw 60 to 150 amps with no load on
it and up to 250 amps under load (while cranking the engine). The no load amp
draw will vary depending on the type of starter. If the amp draw is too high, the
starter needs to be replaced. The same is true if the starter doesn't achieve the
specified rpm.
Sometimes the starter motor works fine but the drive gear won't engage the ring
gear on the flywheel. If the drive gear mechanism can be replaced separately,
there's no need to replace the entire starter. A bad solenoid can also cause starter
problems. The solenoid acts like a relay to route power directly to the starter from
the battery. It may be mounted on the starter or located elsewhere in the engine
compartment and is usually connected to the positive battery cable. Corrosion, poor
ground at the solenoid mount or poor battery cable connections will prevent the
solenoid from doing its job.
If the starter tests okay but fails to crank, another possible cause may be a bad
file:///C|/Users/Steve/Documents/Volvo%20FAQ%20Updated/ElectricalStarting.html[01/13/14 10:02:47 PM]
start inhibitor switch,
or
bad wiring
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