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Home >> Mazda >> 2005 >> MX-5 Miata Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Symptom Troubleshooting [Engine Control System BP, BP With TC) >> No.31 Spark Plug Condition >> Diagnostic Procedure

Diagnostic Procedure

NO.31 SPARK PLUG CONDITION [BP, BP WITH TC] DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1
  • Remove all spark plugs.
  • Inspect spark plug condition.
  • Is spark plug condition okay?
 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
  • Is spark plug wet/covered with carbon by engine oil?
 Yes Inspect all areas related to oil pumping.
No Go to the next step.
3
  • Inspect spark plug for following.
    • Cracked insulator
    • Heating value
    • Air gap
    • Worn electrode
  • Is spark plug okay?
 Yes Go to the next step.
No Replace spark plug.
4
  • Inspect compression pressure at suspected faulty cylinder.
  • Is compression pressure correct?

    (See COMPRESSION INSPECTION )

 Yes Go to the next step.
No Repair or replace malfunctioning part.
5
  • Install all spark plugs.
  • Carry out spark test at suspected faulty cylinder.
  • Is strong blue spark visible? (Compare with normal cylinder.)
 Yes Go to the next step.
No Repair or replace malfunctioning part.
6 Yes Inspect fuel injector for following:
  • Open or short in injector
  • Leakage
  • Injection volume
No Zero or low: 
  • Inspect FP circuit.
  • Inspect for FP relief valve open.
  • Inspect for fuel leakage inside pressure regulator.
  • Inspect for clogged main fuel line.
  • Inspect pulsation damper.

High: 
  • Inspect pressure regulator for high pressure cause.
  • Inspect for clogged fuel return line.
7
  • Inspect spark plug for following.
    • Heating value
    • Air gap
  • Are they okay?
 Yes Go to the next step.
No Replace spark plug.
8 Yes Inspect for open circuit between suspected fuel injector connector terminal and following PCM connector terminals:
  • For #1 cylinder:  2A
  • For #2 cylinder:  2D
  • For #3 cylinder:  2G
  • For #4 cylinder:  2J
No Replace fuel injector.
9
  • Is ACL element free of restrictions?
 Yes Go to the next step.
No Replace ACL element.
10
  • Carry out spark test.
  • Is strong blue spark visible at each cylinder?
 Yes Go to the next step.
No Repair or replace malfunction part.
11
  • Carry out fuel line pressure inspection.
  • Is fuel line pressure correct?
Fuel line pressure 370-420 kPa {3.7-4.3 kgf/cm2, 53-61 psi} 		 Yes Go to the next step.
No Zero or low: 
  • Inspect FP circuit.
  • Inspect for open FP relief valve.
  • Inspect for fuel leakage inside pressure regulator.
  • Inspect for clogged main fuel line.
  • Inspect pulsation damper.

High: 
  • Inspect pressure regulator for high pressure cause.
  • Inspect for clogged fuel return line.
12
  • Inspect following PIDs.
  • Are PIDs okay?
 Yes Go to the next step.
No Repair or replace malfunctioning part.
13
  • Inspect purge solenoid valve and related vacuum hoses. (When engine can be started)

    (See PURGE SOLENOID VALVE INSPECTION )

  • Are purge solenoid valve and related vacuum hoses okay?
 Yes Go to the next step.
No Repair or replace malfunctioning part.
14
  • Carry out compression inspection.
  • Is compression correct?
 Yes Inspect clogging in exhaust system.
No Repair or replace malfunctioning part.
15
  • When engine cannot be started, inspect intake-air system for air leakage.
  • When engine can be started, carry out intake manifold vacuum inspection.
  • Is air sucked in from intake-air system?
 Yes Repair or replace malfunctioning part.
No Go to the next step.
16
  • Carry out fuel line pressure inspection.
  • Is fuel line pressure correct?
Fuel line pressure 370-420 kPa {3.7-4.3 kgf/cm2, 53-61 psi} 		 Yes Inspect following PIDs.
Inspect PCM GND condition.
No Zero or low: 
  • Inspect FP circuit.
  • Inspect for open FP relief valve.
  • Inspect for fuel leakage inside pressure regulator.
  • Inspect for clogged main fuel line.
  • Inspect pulsation damper.

High: 
  • Inspect pressure regulator for high pressure cause.
  • Inspect for clogged fuel return line.
17
  • Verify test results.
    • If okay, return to diagnostic index to service any additional symptoms.
    • 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 PCM.
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