MerCruiser 305 CID (5.0L) Service Manual page 625

FUEL INJECTION SYSTEM TROUBLESHOOTING
Backfire Symptom (Continued)
Step
10
11
12
13
14
15
Index
Page 5F-24
Action
1. Check for proper ignition voltage input to
the ECM.
2. Check for intermittent open or short to
ground on the ignition voltage input circuit
to the ECM.
Was a problem found?
1. Remove spark plugs, check for wet plugs,
cracks, wear, improper gap, burned elec-
trodes or heavy deposits.
• Refer to Distributor Ignition System in
"Description and System Operation" sec-
tion.
NOTE: If park plugs are gas or oil fouled, the
cause of the fouling must be determined before
replacing the spark plugs
Were spark plugs damaged?
1. Check for intermittent opens or short to
grounds in the MAP sensor and TP sensor
circuits. Also check for throttle linkage
sticking, binding or worn.
2. An intermittent failure may not store a DTC.
Was a problem found?
1. Check engine mechanical for the following
conditions:
• Low compression.
• Sticking or leaking valves.
• Worn camshaft lobe(s).
• Incorrect valve timing.
Was a problem found?
1. Check Intake and exhaust manifold(s) for
casting flash.
Was a problem found?
1. Review all diagnostic procedures within
this table.
2. If all procedures have been completed and
no malfunctions have been found, review/
inspect the following:
• Visual/physical inspection.
• Scan tool data.
• All electrical connections within a sus-
pected circuit and/or system.
Was a problem found?
SERVICE MANUAL NUMBER 24
Yes No
PROCEED TO
Step 11
Step 12
Step 13
Step 14
Step 15
Contact
MerCruiser
Customer
Service
OBD
90-861327--1 OCTOBER 1999