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Home >> Mazda >> 2006 >> MX-5 Miata Base >> Repair and Diagnosis >> Engine Performance >> System >> Symptom Troubleshooting [Engine] >> No.29 Spark Plug Condition >> Diagnostic Procedure

Diagnostic Procedure

SPARK PLUG CONDITION DIAGNOSTIC PROCEDURE TABLE

STEP INSPECTION RESULTS ACTION
1 Remove all the spark plugs.
Inspect spark plug condition.
Is spark plug condition normal?		 Yes Troubleshooting completed.
No Specific plug is wet or covered with carbon: 
Go to the next step.
Specific plug looks grayish white: 
Go to Step 7.
All plugs are wet or covered with carbon: 
Go to Step 9.
All plugs look grayish white: 
Go to Step 15.
2 Are the spark plug wet/covered with carbon by the engine oil? Yes Inspect all areas related to oil, working up and down.
No Go to the next step.
3 Inspect the spark plug for the following:
  • Cracked insulator
  • Heat range
  • Air gap
  • Worn electrode

Is the spark plug normal?		 Yes Go to the next step.
No Replace the spark plug.
(See SPARK PLUG REMOVAL/INSTALLATION .)
4 Inspect compression pressure at suspected malfunctioning cylinder.
Is compression pressure correct?
(See COMPRESSION INSPECTION .)		 Yes Go to the next step.
No Repair or replace the malfunctioning part.
5 Install all spark plugs.
Perform the spark test at suspected malfunctioning cylinder.
Is strong blue spark visible?
(Compare with normal cylinder.)		 Yes Go to the next step.
No Repair or replace the malfunctioning part.
6 Install the fuel pressure gauge between fuel filter and fuel distributor.
Short check connector terminal F/P to body GND using a jumper wiring.
Turn the ignition switch to the ON position (Engine off).
Is the fuel line pressure correct with the ignition switch at ON?
(See FUEL LINE PRESSURE INSPECTION .)		 Yes Inspect fuel injector for the following:
  • Open or short circuit in injector
  • Leakage
  • Injection volume
No Zero or low: 
Inspect the fuel pump relay and fuel pump circuit.
Inspect the fuel line for clogging.
If there is no malfunction, replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
High: 
Replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
7 Inspect the spark plug for the following.
  • Heat range
  • Air gap

Is the spark plug normal?

 Yes Go to the next step.
No Replace the spark plug.
(See SPARK PLUG REMOVAL/INSTALLATION .)
8 Remove the suspected fuel injector.
Inspect the following:
Are all above items normal?		 Yes Inspect for open circuit in wiring harness between fuel injector connector terminal B and PCM at the following terminals:
  • For No.1 cylinder: 2BB 
  • For No.2 cylinder: 2BC 
  • For No.3 cylinder: 2BD 
  • For No.4 cylinder: 2AZ 
No Replace the fuel injector.
9 Is the air cleaner element free of clogging? Yes Go to the next step.
No Replace the air cleaner element.
10 Perform the spark test.
(See SPARK TEST  .)
Is strong blue spark visible at each cylinder?		 Yes Go to the next step.
No Repair or replace the malfunctioning part.
11 Install the fuel pressure gauge between the fuel filter and fuel distributor.
Short check connector terminal F/P to body GND using a jumper wiring.
Turn the ignition switch to the ON position (Engine off).
Is the fuel line pressure correct with ignition switch at ON?
(See FUEL LINE PRESSURE INSPECTION .)		 Yes Go to the next step.
No Zero or low: 
Inspect the fuel pump relay and fuel pump circuit.
Inspect the fuel line for clogging.
If there is no malfunction, replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
High: 
Replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
12 Inspect the following PIDs:
  • ECT
  • O2S11 (When engine can be started.)
  • O2S12 (When engine can be started.)
  • MAF

(See PCM INSPECTION .)
Are PIDs normal?		 Yes Go to the next step.
No Repair or replace the malfunctioning part.
13 Perform the purge control inspection.
(When engine can be started.)
(See PURGE CONTROL SYSTEM INSPECTION  .)
Is the purge control correct?		 Yes Go to the next step.
No Repair or replace the malfunctioning part.
14 Perform compression inspection.
(See COMPRESSION INSPECTION .)
Is compression correct?		 Yes Visually inspect for deformed exhaust system part.
No Repair or replace the malfunctioning part.
15 When the engine cannot be started, inspect the intake-air system for air leakage.
When the engine can be started, perform intake manifold vacuum inspection.
Is air sucked in from intake-air system?		 Yes Repair or replace the malfunctioning part.
No Go to the next step.
16 Install the fuel pressure gauge between the fuel filter and the fuel distributor.
Short check connector terminal F/P to body GND using a jumper wiring.
Turn the ignition switch to the ON position (Engine off).
Is fuel line pressure correct with the ignition switch at ON?
(See FUEL LINE PRESSURE INSPECTION .)		 Yes Inspect the following PIDs:
  • ECT
  • O2S11
  • O2S12
  • MAF

(See PCM INSPECTION .)
Inspect PCM GND condition.
No Zero or low: 
Inspect the fuel pump relay and fuel pump circuit.
Inspect the fuel line for clogging.
If there is no malfunction, replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
High: 
Replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION .)
17
  • Verify test results.
    • If normal, return to diagnostic index to service any additional symptoms.

      (See ENGINE SYMPTOM TROUBLESHOOTING  .)

    • If malfunction remains, inspect related Service Bulletins and/or On-line Repair Information and perform repair or diagnosis.
      • If vehicle is repaired, troubleshooting completed.
      • If vehicle is not repaired or additional diagnostic information is not available, replace the PCM.

        (See PCM REMOVAL/INSTALLATION .)
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