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2008 - MX-5 - Engine

NO.12 LACK/LOSS OF POWER-ACCELERATION/CRUISE [LF]



12

LACK/LOSS OF POWER—ACCELERATION/CRUISE

DESCRIPTION

Performance is poor under load (such as power down when climbing hills).

POSSIBLE CAUSE

  • Improper A/C system operation

  • Erratic signal or no signal from CMP sensor

  • Air leakage from intake-air system parts

  • Restriction in intake-air system

  • Intake air temperature too hot

  • Improper variable intake air control operation

  • Improper operation of electronic throttle control system

  • Purge control solenoid malfunction

  • Improper EGR valve operation

  • Brake dragging

  • Erratic signal from CKP sensor

  • Low engine compression

  • Vacuum leakage

  • Poor fuel quality

  • Erratic signal to ignition coil

  • Engine overheating

  • Throttle body malfunction

  • Spark plug malfunction

  • PCV valve malfunction

  • Improper valve timing due to jumping out of timing belt

  • Improper variable valve timing control operation

  • Restriction in exhaust system

  • Intermittent open or short in fuel pump related circuit

  • Inadequate fuel pressure

  • Fuel pump mechanical malfunction

  • Fuel line restriction or clogging

  • Fuel leakage from fuel injector

  • Fuel injector clogging

  • Erratic signal from accelerator pedal position sensor

  • Erratic signal from TP sensor

  • Intermittent open or short circuit in MAF sensor, Accelerator pedal position sensor, TP sensor, IAT sensor and VSS

  • AT malfunction (AT)

  • Clutch slippage (MT)

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

Verify the following:

  • Vacuum connection

  • Restriction in intake-air system (such as air cleaner element, fresh air duct)

  • No air leakage from intake-air system

  • No restriction of intake-air system

  • Proper sealing of intake manifold and components attached to intake manifold; such as EGR valve

  • Fuel quality (such as proper octane, contamination, winter/summer blend)

Are all items normal?

Yes

Go to the next step.

No

Service if necessary.

Repeat Step 1.

2

Connect the M-MDS to the DLC-2.

Turn the ignition switch to the ON position (Engine off).

Retrieve any DTCs.

Are there any DTCs displayed?

Yes

DTC is displayed:

Go to the appropriate DTC inspection.

(See DTC TABLE [LF].)

No

No DTC is displayed:

Go to the next step.

3

Is the engine overheating?

Yes

Go to symptom troubleshooting "No.17 Cooling system concerns-Overheating".

No

Go to the next step.

4

Connect the M-MDS to the DLC-2.

Access APP1, APP2, RPM, MAF, TP, IAT and VSS PIDs.

Drive vehicle while monitoring PIDs.

Are PIDs within specifications?

(See PCM INSPECTION [LF].)

Yes

Go to the next step.

No

APP1, APP2 PIDs:

Inspect if output signal accelerator pedal position sensor changes smoothly.

RPM PID:

Inspect CKP sensor and related wiring harness for vibration or intermittent open/short circuit or both.

MAF PID:

Inspect for intermittent open circuit of MAF sensor and related wiring harness.

TP PID:

Inspect if output signal TP sensor changes smoothly.

IAT PID:

Inspect for air suction in intake-air system.

If normal, inspect intermittent short circuit of IAT sensor and related wiring harnesses.

VSS PID:

Inspect for intermittent open circuit of VSS and related wiring harness.

5

Visually inspect the CKP sensor and teeth of crankshaft pulley.

Are the CKP sensor and teeth of crankshaft pulley normal?

Yes

Go to the next step.

No

Replace the malfunctioning part.

6

Inspect the spark plug condition.

Is spark plug wet, covered with carbon or grayish white?

Yes

Spark plug is wet or covered with carbon:

Inspect the fuel injector for fuel leakage.

Inspect spark plug and high-tension lead.

Spark plug is grayish white:

Inspect the fuel injector for clogging.

No

Install the spark plugs on original cylinders.

Go to the next step.

7

Remove and shake the PCV valve.

Does the PCV valve rattle?

Yes

Go to the next step.

No

Replace PCV valve.

8

Perform electronic throttle control system operation inspection.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Does electronic throttle control system function properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part according to electronic throttle control system operation inspection results.

9

visually inspect deformed exhaust system part.

Is there any deformed exhaust system part?

Yes

Replace the suspected part.

No

Go to the next step.

10

Install the fuel pressure gauge between the fuel pipe 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.

Is fuel line pressure correct with ignition switch to ON position?

(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].)

11

Inspect variable intake air control operation.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Does VIS function properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part.

12

NOTE:

  • The following test is for engine stalling with the A/C on concern. If other symptoms exist, go to the next step.

Connect pressure gauge to the A/C low and high side pressure lines.

Turn the A/C on and measure low side and high side pressures.

Are pressures within specifications?

(See REFRIGERANT PRESSURE CHECK.)

Yes

Go to the next step.

No

If A/C is always on, go to symptom troubleshooting "No.24 A/C is always on or A/C compressor runs continuously".

(See NO.24 A/C IS ALWAYS ON/A/C COMPRESSOR RUNS CONTINUOUSLY [LF].)

For other symptoms, inspect the following:

  • Refrigerant charging amount

  • Condenser fan operation

13

Inspect for A/C cut‐off operation.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Does the A/C cut-off function properly?

Yes

Go to the next step.

No

Inspect A/C cut‐off system components.

14

Disconnect the vacuum hose between the purge solenoid valve and the intake manifold from purge solenoid valve side.

Plug opening end of vacuum hose.

Drive the vehicle.

Does the engine condition improve?

Yes

Inspect if purge solenoid valve is stuck open mechanically.

Inspect the evaporative emission control system.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

No

Go to the next step.

15

Visually inspect the CMP sensor and projections of camshaft pulley.

Are the CMP sensor and projections of camshaft pulley normal?

Yes

Go to the next step.

No

Replace the malfunctioning part.

16

Inspect EGR system.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Is EGR system normal?

Yes

Go to the next step.

No

Replace the malfunctioning part according to EGR control system operation inspection results.

17

Inspect the variable valve timing control system operation.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Does the variable valve timing control system function properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part according to variable valve timing control system inspection results.

18

Is the engine compression correct?

Yes

Inspect the following:

  • Valve timing

  • Internal transaxle components (AT)

  • Clutch (MT)

  • Brake system for dragging

No

Inspect for cause.

19

  • 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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