Test 26 - Check Ignition Coil - DeWalt DXGN4500 Manual

Section 3 Engine Diagnostic Tests
Check Compression
To check engine compression, remove spark plug. Insert
an automotive type compression gauge into the spark
plug hole. Crank engine until there is no further in
pressure. The highest reading obtained is engine
compression pressure.
Minimum Allowable Compression Pressure Cold
Engine – 60 psi
If compression is poor, look the following causes:
• Loose cylinder head bolts
• Failed cylinder head gasket
• Burned valves or valve seats
•
Insufficient valve clearance
• Warped cylinder head
•
Warped valve stem
• Worn or broken piston ring(s)
• Worn or damaged cylinder bore
• Broken connecting rod
• Worn valve seats or valves
•
Worn valve guides
NOTE: Refer to Engine Service Manual Part Number
0C1103A for further engine service information on the
engine.
Test 26 – Check Ignition Coil
General Theory
The ignition system used on GH-220 engines is a solid-
state (breakerless) type. The system utilizes a magnet on
the engine flywheel to induce a relatively low voltage into
an ignition coil assembly.
components increases voltage and delivers the high
voltage across spark plug gap.
The ignition coil houses a solid-state circuit board
controlling ignition timing. Timing is fixed, air gap is non-
adjustable, and spark advance is automatic.
Major components of the ignition system include (a)
ignition coil assembly, (b) spark plug, and (c) engine
flywheel.
Solid-state components encapsulated in ignition coil are
not accessible and cannot be serviced. If coil is defective,
replace assembly. The air gap between the coil and
flywheel magnet is fixed and non-adjustable.
See Figure 1-13. The ignition coil assembly consists of
(a) ignition coil, (b) spark plug high tension lead, and (c)
spark plug boot.
34
Ignition coil internal
Figure 1-13. Ignition Coil
Procedure
Disconnect Wire 18 at bullet connector and repeat
1.
Test 20.
If unit produces spark, a short to ground exists on
2.
Wire 18 between the Ignition Coil and RUN-STOP
switch.
If unit still failed to produce spark, proceed to Step
3.
4.
Set a DMM to measure resistance. Connect
4.
negative (-) test lead to Wire 18, going to the coil.
Connect positive (+) test lead to frame ground.
Approximately 1.5 kΩ should be measured.
Set a DMM to measure resistance. Disconnect
5.
high tension lead from spark plug. Connect one
test lead to high tension lead. Connect other test
lead to frame ground. Approximately 16 kΩ should
be measured.
Results
If unit was able to produce spark after disconnect-
1.
ing Wire 18, a short to ground or a faulty switch is
supplying Wire 18 with a ground inhibiting the
engine from producing spark.
If Ignition Coil fails Step 4 or Step 5 by a high
2.
margin, replace Ignition Coil.
If coil passes Step 4 and Step 5 but there is still no
3.
spark, replace ignition coil.
NOTE: Before replacing ignition coil, check flywheel
magnet.
Checking Flywheel Magnet
The flywheel magnet rarely loses magnetism. To
determine if a magnet is be defective, perform this test:
Place flywheel on a wooden surface.
1.
Hold a screwdriver at the utmost end of handle with
2.
its point down.
Move tip of screwdriver to about 3/4 inch (19mm)
3.
from magnet. The screwdriver blade should be
pulled in against magnet.
001696
Diagnostic Repair Manual