Poor Fuel Economy Symptom - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Poor Fuel Economy Symptom

Step
Definition: Fuel economy is noticeably lower than expected. Also, economy is noticeably
lower than it was on this engine at one time.
Index
90-861326--1 MARCH 1999
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Action
Was the "On-Board Diagnostic" (OBD)
1
System Check performed?
Was visual/physical check performed?
2
1. Check operators driving habits. Are
excessively heavy loads being car-
ried? Is operator accelerating too
much, too often?
3
2. If a problem is found, repair as nec-
essary.
Was a problem found?
1. Check flame arrestor for dirt or being
plugged.
2. Check for fuel leaks.
4
3. If a problem is found, repair as nec-
essary.
Was a problem found?
1. Check for proper fuel pressure.
Refer to Table A-4 in "General Sys-
tem Diagnostics" section.
5
2. If a problem is found, repair as nec-
essary.
Was a problem found?
1. Check for proper operation of Igni-
tion Control (IC) circuit and the
Knock Sensor (KS) circuit.
6
2. If a problem is found, repair as nec-
essary.
Was a problem found?
1. Remove spark plugs, check for wet
plugs, cracks, wear, improper gap,
burned electrodes or heavy depos-
its.
Refer to Distributor Ignition System.
NOTE: If spark plugs are gas or oil
7
fouled, the cause of the fouling must be
determined before replacing the spark
plugs.
2. If a problem is found, repair as nec-
essary.
Was a problem found?
FUEL INJECTION SYSTEM TROUBLESHOOTING
Value(s) Yes
- Go to Step 2
- Go to Step 3
System nor-
-
mal
Go to OBD
System
-
Check
Go to OBD
System
-
Check
Go to OBD
System
-
Check
Go to OBD
System
-
Check
No
Go to OBD
System Check
Go to Visual/
Physical
Check
Go to Step 4
Go to Step 5
Go to Step 6
Go to Step 7
Go to Step 8
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