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2008 - MX-5 - Engine

NO.29 SPARK PLUG CONDITION [LF]



29

SPARK PLUG CONDITION

DESCRIPTION

Incorrect spark plug condition

POSSIBLE CAUSE

NOTE:

  • Inspecting spark plugs condition can determine whether problem is related to a specific cylinder or possibly all cylinders.

    Wet/carbon stuck on specific plug:
  • Spark—Weak, not visible

  • Air/fuel mixture—Excessive fuel injection volume

  • Compression—No compression, low compression

  • Malfunction spark plug

    Grayish white with specific plug:
  • Air/fuel mixture—Insufficient fuel injection volume

  • Malfunction spark plug

    Wet/carbon is stuck on all plugs:
  • Spark—Spark weak

  • Air/fuel mixture—Too rich

  • Compression—Low compression

  • Clogging in intake/exhaust system

    Grayish white with all plugs:
  • Air/fuel mixture—Too lean

WARNING:

The following troubleshooting flow chart contains the fuel system diagnosis and repair procedures. Read the following warnings before servicing the fuel system:
  • Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage. Always keep sparks and flames away from fuel.

  • Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries or death and damage. Fuel can also irritate skin and eyes. To prevent this, always complete “BEFORE SERVICE PRECAUTION” and “AFTER SERVICE PRECAUTION” described in this manual.

    (See BEFORE SERVICE PRECAUTION [LF].)

    (See AFTER SERVICE PRECAUTION [LF].)

CAUTION:

  • Disconnecting/connecting quick release connector without cleaning it may cause damage to fuel pipe and quick release connector. Always clean quick release connector joint area before disconnecting/connecting, and make sure that it is free of foreign material.


Diagnostic procedure

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 [LF].)

4

Inspect compression pressure at suspected malfunctioning cylinder.

Is compression pressure correct?

(See COMPRESSION INSPECTION [LF].)

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 [LF].)

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 [LF].)

High:

Replace the fuel pump unit.

(See FUEL PUMP UNIT REMOVAL/INSTALLATION [LF].)

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 [LF].)

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 ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

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 [LF].)

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 [LF].)

High:

Replace the fuel pump unit.

(See FUEL PUMP UNIT REMOVAL/INSTALLATION [LF].)

12

Inspect the following PIDs:

  • ECT

  • O2S11 (When engine can be started.)

  • O2S12 (When engine can be started.)

  • MAF

(See PCM INSPECTION [LF].)

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 ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

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 [LF].)

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 [LF].)

Yes

Inspect the following PIDs:

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 [LF].)

High:

Replace the fuel pump unit.

(See FUEL PUMP UNIT REMOVAL/INSTALLATION [LF].)

17

  • Verify test results.

    • If normal, return to diagnostic index to service any additional symptoms.

      (See SYMPTOM DIAGNOSTIC INDEX [LF].)

    • 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 [LF].)




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