FUEL INJECTION SYSTEM TROUBLESHOOTING
SERVICE MANUAL NUMBER 24
Page 5F-20
90-861327--1 OCTOBER 1999
Poor Fuel Economy Symptom
Step
Action
Yes
No
PROCEED TO
Definition: Fuel economy is noticeably lower than expected. Also, economy is
noticeably lower than it was on this engine at one time.
1
Was the “On-Board Diagnostic” (OBD)
System Check performed?
Step 2
OBD
2
Was visual/physical check performed?
Step 3
Visual/ Physical
Check
3
1. .Check operators driving habits. Are
excessively heavy loads being carried? Is
operator accelerating too much, too often?
Was a problem found?
System normal
Step 4
4
1. Check flame arrestor for dirt or being
plugged.
2. Check for fuel leaks.
Was a problem found?
Step 5
5
1. Check for proper fuel pressure.
•
Refer to Table A-4 in “General System
Diagnostics” section.
Was fuel pressure 30 psi for EFI or 3–7 psi
for carbureted engines?
Step 6
6
1. Check for proper operation of Ignition Con-
trol (IC) circuit and the Knock Sensor (KS)
circuit.
Was a problem found?
Step 7
7
1. Remove spark plugs, check for wet plugs,
cracks, wear, improper gap, burned elec-
trodes or heavy deposits.
•
Refer to Distributor Ignition System.
NOTE: If spark plugs are gas or oil fouled, the
cause of the fouling must be determined
before replacing the spark plugs.
Were spark plugs damaged?
Step 8
8
1. Visual (physically) check vacuum hoses
for splits, kinks and improper connections
and routing.
Was a repair required?
Step 9
9
1. Check engine compression for being low.
Was a problem found?
OBD
Step 10
Index
