MerCruiser 305 CID (5.0L) Service Manual page 669

DIAGNOSTICS
Chart A-7 (5 of 6): Ignition System Check
Step
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
Index
Page 5G-42
a. Disconnect distributor 4-wire connector.
b. Remove distributor cap.
c. Disconnect pick-up coil connector from the distributor
ignition control module.
d. Connect D\/OM to CKT 121 tach terminal at the 5-way
or 6-way harness connector and ground.
e. Ignition ON, engine OFF.
f. Connect positive (+) end of a known good 1.5 volt test
battery to the "P" terminal on the distributor ignition con-
trol module. Observe the voltage at the tach terminal as
the negative (-) end of the test battery is momentarily
grounded to a known good ground.
Does The Voltage Drop?
Check for spark from the coil wire as the test battery lead
is removed?
Is Adequate Spark Present?
Replace ignition coil and recheck for spark using Steps 10.
and 11.
Is Adequate Spark Present?
Reinstall coil and check coil wire from distributor cap. If OK,
replace ignition module.
Check for faulty connections or open tach lead. If OK,
replace ignition module and recheck for spark using Steps
10. and 11.
Is Adequate Spark Present?
Replace ignition coil.
Is the rotating pole piece still magnetized?
Replace faulty pick-up coil.
Inspect distributor cap for water, cracks, etc. If OK, replace
faulty distributor rotor.
Check for open or short to ground in CKT 3, open CKT 902,
open or short to ground in CKT 121. If OK, replace faulty
ignition coil.
Check ignition module ground. If OK, replace faulty ignition
module.
Replace distributor pole piece and shaft assembly.
A mechanical repair will be necessary before continuing
with this test.
Locate and repair intermittent faulty connections.
Action
SERVICE MANUAL NUMBER 24
Yes No
PROCEED TO
Step 11. Step 20.
Step 16. Step 12.
Step 13. –
–
Verify
Step 15.
Repair
–
Step 17. Step 21.
Verify Verify
–
Repair
90-861327--1 OCTOBER 1999