MerCruiser 305 CID (5.0L) Service Manual page 668

SERVICE MANUAL NUMBER 24
Chart A-7 (4 of 6): Ignition System Check
Step
1.
2.
3.
4.
5.
6.
7.
8.
9.
Index
90-861327--1 OCTOBER 1999
Was the "On-Board Diagnostic" (OBD) System Check
Performed?
a. Check spark plug wires for open circuits, cracks in
insulation, or improper seating of terminals at spark
plugs, distributor cap, and coil tower before proceeding
with this table.
b. Disconnect 5-way or 6-way harness connectors.
c. Install a temporary jumper wire between CKT 3 and the
purple ignition lead in the harness connectors.
d. Attempt to start engine and check tor secondary spark.
If there is "no spark" at one wire, check a few more
wires. A few sparks and then nothing is considered "no
spark."
Is Adequate Spark Present?
Remove distributor cap and verify rotation of distributor
rotor.
Is The Distributor Rotor Turning?
Do you have a MEFI 3 ECM and a distributor with a
two-wire connection?
a. Disconnect distributor 4-wire connector.
b. Check for secondary spark.
Is Adequate Spark Present?
a. Reconnect distributor 4-wire connector.
b. Check for secondary spark from the coil tower using a
known good coil wire.
Is Adequate Spark Present?
a. Disconnect distributor 2-wire connector.
b. Ignition ON, engine OFF.
c. Using DVOM, check voltage at both terminals.
Is Voltage Reading Greater Than 10 Volts?
a. Reconnect distributor 2-wire connector.
b. Ignition ON engine OFF.
c. Using DVOM, check voltage from CKT 121 tach termi-
nal to ground.
Is Voltage Reading Greater Than 10 Volts?
a. Using a test light connected to ground , probe CKT 121
tach terminal at the 5-way or 6-way harness connector.
b. Observe the test light while cranking engine.
Is Test Light Blinking?
Action
DIAGNOSTICS
Yes No
PROCEED TO
Step 2. OBD
Step 23. Step 3.
Step 4. Step 22.
Step 24. Step 5.
Step 17. Step 6.
Step 18. Step 7.
Step 8. Step 19.
Step 9. Step 14.
Step 12. Step 10.
Page 5G-41