Knocking - Mazda MX-5 1990 Workshop Manual

F
TROUBLESHOOTING GUIDE
27
[TROUBLESHOOTING HINTS]
0)
Air/Fuel mixture too lean
• Fuel injection amount incorrect
• Fuel line pressure decreases while accelerating
STEP INSPECTION
Check if "00" is displayed on Self-Diagnosis
Checker with ignition switch ON
u
page F-78
2 Check switches for correct operation with Self-
Diagnosis Checker Monitor Lamp and ignition
switch ON
MONITO
LAMP
3 Check if ECU terminal voltages are OK
(20, 20 and 20)
c::::r page F-129
4 Check for correct intake manifold vacuum at idle
Vacuum: More than 450 mmHg (17.7 inHg)
5 Check if air cleaner element is clean
u
page F-75
6 Check for correct engine compression
F-66
c::::r page 8-10
Engine compression: 1,324-932 kPa
(13.5-9.5 kg/cm
2
,
192-135 psi) - 300 rpm
KNOCKING
®
Incorrect ignition timing (too advance)
@
Overheating
@ Carbon deposits in engine
ACTION
Yes Go to next step
No Malfunction Code No. displayed
Check for cause (Refer to specified
check sequence)
"88" flashes
Check ECU terminal
1
F voltage
Voltage: Approx. 12V
(Ignition switch ON)
L7'
page F-80
c::::r page F-128
=:> If OK, replace ECU
c::::7'
page F-127
=:>
If not OK, check wiring between
ECU and Self-Diagnosis Checker
c::::r
page F-7
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 D
c::::7'
page F-90
and Self-Diagnosis Checker
c::::7'
page F-7
Yes Go to next step
No Check for cause (Refer to "Check Point
for Each Terminal")
Yes Go to next step
No Check for air leakage of intake air sys-
tem components
Yes Go to next step
No Replace air cleaner element
Yes Go to next step
No
High compression
Check engine condition
• Carbon deposits
c::::r page F-128
c::::r page F-93
c::r page F-92
c::::r page 9-10