Poor Fuel Economy - Mazda MX-5 1990 Workshop Manual

F
TROUBLESHOOTING GUIDE
31
POOR FUEL ECONOMY
[TROUBLESHOOTING HINTS]
While fuel consumption is drastically increased during city driving, short-run operation, stop and go driving, extended win-
ter warm-up periods, etc" as opposed to "trip" mileage, an attempt should be made to determine these factors when con-
fronted with "poor mileage" conditions, However, since the operator is not always at fault, the following is offered,
CD
Operator depressing accelerator more than usual due to
low engine power
@
Alcohol blended fuel used
@
High vehicle load
• Poor ignition
• Low intake air amount
• Electric spark advance control malfunction
• Clutch slipping
• Exhaust component restricted
®
Air/Fuel mixture too rich
• High fuel line pressure
STEP
INSPECTION
• Low ti re pressu re
• Unrecommended tire used
• Brake dragging
®
Fuel cut control malfunction
®
High idle speed
(Refer to page
F-36)
ACTION
Check factors other than engine Yes Go to next step
• Low tire pressure
CT
page Q-3
• Unrecommended tire used
u
page 0-2
• Clutch slipping
L7'
page H-3
No Repair
• Brake dragging c::::r page P-27
• Exhaust component resticted
CT
page F-115
2 Check if air hoses are connected correctly
CT
page F-93
3 Check if air cleaner element is clean
c::7
page F-75
4 Check if "00" is displayed on Self-Diagnosis
Checker with ignition switch ON
CT
page F-78
5 Check switches for correct operation with Self-
DiagnosIs Checker Monitor Lamp and ignition
switch ON
c::::r page F-89
Yes Go to next step
No Repair
Yes Go to next step
No Replace
Yes Go to next step
No
Malfunction Code No. displayed
Check for cause (R'efer to specified
check sequence)
"88" flashes
Check ECU terminal 1 F voltage
Voltage: Approx. 12V
(Ignition switch ON)
¢
If OK, replace ECU
¢
If not OK, check wiring between
ECU and Self-Diagnosis Checker
Yes Go to next step
No
Lamp not ON/OFF with specified
switch
Check for cause (Refer to specified
check sequence)
Lamp always ON
Check wiring between ECU terminal 1 F
c::7
page F-93
c::::r page F-75
u
page F-80
L7'
page F-128
c::::r page F-127
u
page F-7
CT
page F-90
and Self-Diagnosis Checker
c::7
page F-7
F-70