Chapter
B
: Ignition System Diagnosis and Repair
43
Voltage Drop
Voltage drop is the amount of voltage that an electrical
device normally consumes to perform its task. A small
amount of voltage will always be lost due to normal cir-
cuit resistance. However, excessive voltage drop can be
the result of a high-resistance connection or failed com-
ponent.
To check voltage drop, the circuit must be powered up
and under load. The circuit must also have the maxi-
mum amount of current under normal conditions for
which the circuit was designed. The amount of voltage
drop that is considered acceptable will vary by circuit.
Low-current circuits that draw milliamps will be affect-
ed by very small voltage drops, while the same amount
of voltage drop will have a negligible effect on a high-
current circuit.
To measure voltage drop along a circuit, connect the
negative voltmeter lead to ground and use the positive
meter lead to probe at various points in the circuit. Com-
pute voltage drop by checking available voltage on both
sides of a load, then subtracting the voltage reading of
the ground side from the reading on the positive side of
the load. Take direct voltage drop readings by connect-
ing the positive meter lead to the power side of a load
and connecting the negative meter lead to the ground
side of the component.
Manufacturers provide voltage drop specifications for
various ignition components. Measure the voltage drop
across the ignition module ground as follows:
1. Connect the voltmeter positive lead to the negative
(distributor) coil terminal; connect the voltmeter
negative lead to ground.
2. Switch the ignition on and observe the voltmeter.
Typically, a reading less than 0.5 volt indicates the mod-
ule ground is in good condition.
High voltage drop can be caused by loose connections,
poor ground, or excessive wear. Check and repair
wiring, clean ground circuit, and repeat the test.
Multiple Ignition Coil Designs
The coil packs contain multiple coils each supplying
secondary voltage to two cylinders, figure 2-16. The
coils operate on the same basic principal as their pre-
decessors but are configured differently. Generally each
coil supplies secondary voltage for a pair of cylinders
each time they reach TDC. One cylinder of the pair is on
the power stroke while the other is on the exhaust
stroke. The spark occurring on the exhaust cylinder is of
little value and therefore the system is often called a
waste spark system.
Another more recent design provides an individual coil
for each cylinder, figure 2-17. This coil is mounted on or
near the spark plug is serves. These designs are known
as coil-on-plug or coil-near-plug systems.
Fig. 2-16.
Typical multiple coil coil-pack.
Fig. 2-17.
Typical coil-near-plug ignition coil installation.
Summary of Contents for ASE-A8
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