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Home › Mazda › 2006 › MPV LX › Repair and Diagnosis › Engine Performance › System › Symptom Troubleshooting [Engine Control System AJ) › No. 14 Poor Fuel Economy › Diagnostic procedure

Diagnostic procedure

POOR FUEL ECONOMY DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1
  • Inspect following:
  • Air cleaner element for contamination.
  • ATF level.
  • Fuel quality.
  • Coolant level.
  • Are all items okay?
 Yes Go to next step.
No Service as necessary. Repeat Step 1.
2
  • Connect WDS or equivalent to DLC-2.
  • Turn ignition key to ON (Engine OFF).
  • Retrieve any DTCs.
  • Is "PASSED" displayed?
 Yes No DTC is displayed: 
Go to next step.
No DTC is displayed: 
Go to appropriate DTC test.
3 Yes Go to next step.
No Inspect for coolant leakage. Inspect cooling fan operations or thermostat operations.
4
  • Perform spark test. (See SPARK TEST .)
  • Is strong blue spark visible at each cylinder?
 Yes Inspect for following:
  • Spark plugs malfunction.
  • CMP sensor is installed improperly.
  • Trigger wheel damage on camshaft.
  • Open or short circuit on CMP sensor.
  • Open or short circuit between CMP sensor and PCM terminal 2 or 28.

Repair or replace malfunctioning part.

  • If okay, go to next step.
No Repair or replace malfunctioning part according to spark test results.
5
  • Install fuel pressure gauge between fuel filter and fuel distributor.
  • Start engine and run it at idle.
  • Measure fuel line pressure at idle.
  • Is fuel line pressure correct at idle?

Fuel line pressure 420-460 kPa {4.3-4.6 kgf/cm2, 61-66 psi} 

 Yes Go to next step.
No Zero or low: 
  • Inspect fuel pump circuit.
  • Inspect for open fuel pump relief valve.
  • Inspect for fuel leakage inside pressure regulator.
  • Inspect for clogged main fuel line.

High: 

  • Inspect pressure regulator for high pressure cause.
  • Inspect for clogged fuel return line.
6 Yes Go to next step.
No Repair or replace malfunctioning part.
7
  • Remove and shake PCV valve.
  • Does PCV valve rattle?
 Yes Go to next step.
No Replace PCV valve.
8
  • Inspect for restriction in the exhaust system.
  • Is there any restriction?
 Yes Inspect exhaust system.
No Go to next step.
9
  • Is brake system functioning properly?
 Yes Go to next step.
No Inspect for cause.
10
  • Inspect MAF sensor for contamination.
  • Is there any contamination?
 Yes Replace MAF sensor.
No Go to next step.
11
  • Is engine compression correct?
 Yes Inspect valve timing.
No Inspect for cause.
12
  • 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 or reprogram PCM.
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