Mazda MX-5 1990 Workshop Manual page 191

TROUBLESHOOTING GUIDE
F
STEP INSPECTION
6 Check if throttle linkage is correctly installed and
operates freely
7 Check for correct intake manifold vacuum at idle
Vacuum: More than 450 mmHg (17.7 inHg)
8 Check if air cleaner element is clean
IT
page F-75
9
Check for correct ignition timing at idle
c::::r page F-76
Ignition timing: 10 0
±
1 0 BTDC
G~
klJll1J
CONNECT TERMINALS
10 Check for correct fuel line pressure at idle
c::::r page F-103
Fuel line pressure:
265-314 kPa (2.7-3.2 kg/cm
2
,
38-46 psi)
(Vacuum hose to pressure regulator dis-
connected)
INSTALL CLAMPS
11 Check for correct engine compression
IT
page B-10
Engine compression: 1,324-932 kPa
(13.5-9.5 kg/cm
2
,
192-135 psi) - 300 rpm
12 Try known good ECU and check if condition im-
proves
IT
page F-127
ACTION
Yes Go to next step
No Correct, clean, or replace as required
any binding or damaged linkage and
adjust cable deflection at throttle body c::::r
page F-96
Yes Go to next step
No Check for air leakage of intake air
system components c::::r page F-93
Yes Go to next step
No Replace air cleaner element c::::r page F-92
Yes Check if ignition timing advances when
accelerating
c:::>
If advances, go to next step
¢
If no advance, replace ECU
No Adjust
Yes Check if fuel line pressure decreases
when accelerating quickly
¢
If decreases, check fuel pump
L7
page F-127
c::::r
page F-76
maximum pressure c::::r page F-108
If OK, check fuel line and filter for
clogging
¢
If no decrease, go to next step
No
Low pressure
Check for fuel line pressure while pinch-
ing fuel return hose
~
If fuel line pressure quickly in-
creases, check pressure regulator c::::r page F-111
c:::> If fuel line pressure gradually in-
creases, check for clogging be-
tween fuel pump and pressure
regulator
If not clogged, check fuel pump
maximum pressure
IT
page F-108
High pressure
Check if fuel return line is clogged
c:::> If OK, replace pressure regulator
¢
If not
OK,
replace
Yes Go to next step
c::7
page F-112
No Check engine condition c::::r page 8-10
- Worn piston, piston rings or cylinder
wall
- Defective cylinder head gasket
- Distorted cylinder head
-Improper valve seating
• Valve sticking in guide
05UOFX-035
F-47