1994 MAZDA MX-5 Workshop Manual

TROUBLESHOOTING GUIDE INSPECTION Check for fuel injector operating sound at idle with sound scope or screwdriver Check if battery positive voltage exists at fuel injec- tor connector 6 terminal Disconnect each high-tension lead at idle and check if engine speed decreases equally each time - - - Check if spark plu CARBON BUILDUP PLUG GAP 1.0-1 .l mm (0.040-0.043 in) DAMAGE AND DETERIORATION Check for correct ignition timing at idle page F-76 Ignition timing: 10" +. lo BTDC Check for EGR system malfunction w page F-124 Check for correct fuel line pressure at idle * page F-110 Fuel line pressure: 26-14 kPa f2.7-3.2 kgflcm2, 38-46 psi} (Vacuum hose to pressure reaulator discon- - Yes - No - Yes No - Yes - No - Yes - No Yes No - Yes ACTION Yes - No - Go to Step 8 Go to Step 7 Check if fuel injector resistance is OK page F-119 Resistance: 12-1 632 0 If OK, check wiring between PCME and fuel injector @r page F-7 Q If not OK, replace fuel injector page F-119 Check wiring between PCME and fuel injector page F-7 Disconnect each fuel injector connector at idle and check if engine speed decreases equally each time 0 If OK, go to Step 10 o If not OK, check fuel injector for fuel leakage G= pane F-120 Go to step 9 Check for correct engine compression t@ Section B Q if OK, replace fuel injector t@ page F-119 o If not OK, check for cause (Refer to Section 6) U=S Section B Repair, clean, or replace Section G Check for correct idle speed @ page F-77 Idle speed: 850 -c 50 rpm (MT) 800 2 50 rpm (AT) 0 If OK, go to next step 0 If not OK, adjust idle speed w page F-77 Adjust page F-72 Repair or replace Go to next step Go to next step Low pressure Check fuel line pressure while pinching fuel return hose 3 If fuel line pressure quickly increases, check pressure regulator US= page F-118 3 If fuel line pressure gradually increases, check for clog- ging between fuel pump and pressure regulator If not clogged, check fuel pump maximum pressure E+T page F-115 Try known good PCME and check if condition im- proves w Daae F-144 Gartner Banana

TROUBLESHOOTING GUIDE 9 LOW IDLE SPEEDIROUGH IDLE - BEFORE WARM-UP IESCRIPTION I Engine speed low or engine vibrates excessively at idle during warm-up TROUBLESHOOTING HINTS] D Low intake air amount Mass airflow sensor stuck Air cleaner element clogged Idle s~eed control Q Low fuel injection amount Fuel injection control malfunction (Correction for coolant temperature) O Poor atomization of fuel Air valve [Correction for coolant temperature ] iTEP I Low RVP (summer) fuel used in cold weather INSPECTION ACTION - Yes Check if "00" is displayed on Self-Diagnosis Check- er with ignition switch ON page F-79 GOG next step Diagnostic Trouble Code No. displayed Check for cause (Refer to specified check sequence) trs page F-81 - - "88"flashes Check PCME terminal 1 E voltage page F-145 Specification: Battery positive voltage (Ignition switch ON) 0 If OK, replace PCME @ page F-143 e If not OK, check wiring between PCME and Self-Diagno- sis Checker page F-7 Check switches for correct operation with Self- Diagnosis Checker Monitor Lamp and ignition switch ON ~8 page F-95 SELECT SW A Yes Go to next step Check if PCME terminal voltaaes are OK No - Yes - No - Yes Lamp not ON/OFF with specified switch Check for cause (Refer to specified check sequence) page F-96 Lamp always ON Check wiring between PCME terminal 1 D and Self-Diag- nosis Checker page F-7 Go to next step " (2D, 20 and 2Q) page F-146 Check for cause (Refer to "Check Point for Each Termi- nal") page F-148 Go to next step Check for correct intake manifold vacuum at idle Vacuum: More than 450 mmHg {I?.? inHg) Check for air leakage of intake air system components @ page F-100 INSTALL CLAPS Gartner Banana

F TROUBLESHOOTING GUIDE STEP 5 INSPECTION Check if air cleaner element is clean page F-76 Connect System Selector to data link connector and set Test Switch to "SELF TEST" when engine is cold Check if engine speed decreases as engine warms UD -r tw page F-101 , GND TEN With condition of Step 5 check for correct ignition timing at idle after warm-up G-X page F-76 Ignition timing: 10" + 1" BTDC Try known good PCME and check if condition im- 3roves @S page F-144 - Yes Yes - No - Yes Yes ACTION Go to next step Replace air cleaner element tw page F-99 Go to next step Check air valve @ page F-105 Go to next step Adjust @ page F-76 Replace PCME page F-143 Change fuelto another brand Gartner Banana

TROUBLESHOOTING GUIDE lo 1 LOW IDLE SPEEDIROUGH IDLE - AFTER WARM-UP 3ESCRIPTION I Engine runs normally at idle during warm-up but vibrates excessively after warm-up ;TROUBLESHOOTING HINTS] I> Idle speed control malfunction b AirlFuel mixture too lean Air leakage of intake air system Low fuel line pressure INSPECTION Check if "00" is displayed on Self-Diagnosis Check- er with ignition switch ON m? page F-79 Check switches for correct operation with Self- Diagnosis Checker Monitor Lamp and ignition switch ON page F-95 SELECT SW A Disconnect idle air control valve connector at idle and check if engine condition is charged IAC VALVE - Yes No - Yes - No Yes O Air/Fuel mixture too rich Fuel injection control malfunction (Correction for coolant temperature) @ Poor ignition spark Q Low engine compression ACTION Go to next step Diagnostic Trouble Code No. displayed Check for cause (Refer to specified check sequence) page F-81 "88" flashes Check PCME terminal 1 E voltage page F-145 Specification: Battery positive voltage (Ignition switch ON) 6 If OK, replace PCME page F-143 Q If not OK, check wiring between PCME and Self-Diagno- sis Checker page F-7 Go to next step Lamp not ONIOFF with specified switch Check for cause (Refer to specified check sequence) page F-96 Lamp always ON Check wiring between PCME terminal 1 D and Self-Diag- nosis Checker page F-7 Go to next step Check idle air control valve page F-106 Gartner Banana

F TROUBLESHOOTING GUIDE INSPECTION :heck for correct intake manifold vacuum at idle Vacuum: More than 450 mmHg I17.7 inHg) VACUUM GAUGE :heck if PCME terminal voltages are OK (2D, 20 and 2Q) page F-146 :heck for correct ignition timing at idle @S page F-76 Ignition timing: 10" + 1" BTDC :heck for correct fuel line pressure at idle @S page F-11 0 Fuel line pressure: 265--314 kPa f2.7-3.2 kgf/cm2,38-46 psi} (Vacuum hose to pressure regulator discon- INSTALL CLAPS ' :heck if strong blue spark is visible at each discon- iected high-tension lead while cranking engine - -- :heck for correct engine compression @S Section B Engine compression: 1,255-883 kPa (12.8-9.0 kgf/cm2, 182-128 psi)-300 rpm - Yes Yes Yes No - Yes - No - Yes No - Yes - No - ACTION Go to next step Low vacuum Check for air leakage of intake air system components page F-100 Go to next step Check for cause (Refer to "Check Point for Each Termi- nal") page F148 Check for correct idle speed page F77 Idle speed: 850 -c 50 rpm (Mi) 800 + 50 rpm (AT) e If OK, go to next step o If not OK, adjust idle speed page F-77 Adjust page F-76 Go to next step Low pressure Check fuel line pressure while pinching fuel return hose 0 If fuel line pressure quickly increases, check pressure regulator page F-118 0 If fuel line pressure gradually increases, check for clog- ging between fuel pump and pressure regulator If not clogged, check fuel pump maximum pressure page F-115 Go to next step Check ignition system (Refer to Troubleshooting "Misfire") Section G Go to next step Check engine condition Section B Worn piston, piston rings or cylinder wall Defective cylinder head gasket Distorted cylinder head Improper valve seating Valve sticking in guide Gartner Banana

TROUBLESHOOTING GUIDE INSPECTION :heck if spark plugs are OK WEAR AND CARBQN BUILDUP BURNS PLUG GAP 1 .O-1 .l mm DAMAGE AND t0.040--0.043 in) DETERIORATION DAMAGE Try known good PCME and check if condition im- proves as page F-144 Yes ACTION Go to next step Repair, clean, or replace Section G Gartner Banana

TROUBLESHOOTING GUIDE INSPECTION >heck if throttle valve is closed throttle position Yes when accelerator released I 11 :heck if "00" is displayed on Self-Diagnosis Check- Yes w with ignition switch ON @? page F-79 HIGH IDLE SPEED - AFTER WARM-UP SELECT SW A SYSTEM SELECT 1 FROUBLESHOOTING HINTS] Excessive intake air supplied to engine O Throttle valve not fully closed @ ldle speed control malfunction Air valve not closing ldle air control valve stuck Incorrect coolant temperature signal STEP 1 >heck switches for correct operation with Self- I Yes liagnosis Checker Monitor Lamp and ignition ;witch ON page F-95 SELECT SW A ACTION Go to next step Check if throttle linkage is correctly installed and operates freely @? page F-103 o If OK, go to next step o If not OK, clean, adjust or replace linkage Daae 6103 Go to next step - Diagnostic Trouble Code No. displayed Check for cause (Refer to specified check sequence) @? page F-81 "88" flashes Check PCME terminal 1 E voltage @S page F-145 Specification: Battery positive voltage (Ignition switch ON) 6 If OK, replace PCME E=T page F-143 o If not OK, check wiring between PCME and Self-Diagno- sis Checker @? page F-7 Go to next step Lamp not ONlOFF with specified switch Check for cause (Refer to specified check sequence) E=T page F-96 am^ always ON Check wiring between PCME terminal ID and Self-Diag- IOS~S Checker @? page F-7 Gartner Banana

TROUBLESHOOTING GUIDE INSPECTION Zonnect System Selector to data link connector and set Test Switch to 'SELF TEST" when engine s cold :heck if engine speed decreases as engine warms - T SW. Disconnect idle air control valve connector at idle and check if engine condition is changed IAC VALYE CONNECTOR Pinch PCV hose with pliers and check if engine speed decreases Check if PCME terminal voltages are OK [I R, 2D, 20 and 2Q) page 6146 Yes No - Yes - No - Yes - No - Yes - No ACTION 30 to next step :heck air valve w page -05 30 to next step Check idle air control valve page F-106 Check PCV valve page F-130 30 to next step Try known good PCME page F-144 Check for cause (Refer to "Check Point for Each Termi- ial") page F-148 35UOFX-Oli Gartner Banana