Poor Fuel Economy

WARNING: This page is about a different car, the 2005 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.

POOR FUEL ECONOMY DESCRIPTION

11	POOR FUEL ECONOMY
DESCRIPTION	FUEL ECONOMY UNSATISFACTORY

POOR FUEL ECONOMY INSPECTION/ACTION CHART

STEP	INSPECTION		ACTION
1	PRELIMINARY CHECKS NOTE: Since driving habits can have a significant influence on fuel economy, verify concern before starting an in-depth diagnosis. Also, the following external factors could contribute to "poor fuel economy" conditions: Stop/go city driving. Improper tire pressure/size. Vehicle loads (trailer towing, etc.). Extended winter warm-up conditions. High speed driving. Improper axle ratio. Improper speedometer gear ratio. Road/weather conditions. Aftermarket add-ons. Short-run operations. Customer expectations/driving habits. Perform the following preliminary checks: Air cleaner tube blockage. Contaminated air cleaner element. Transaxle fluid level. Fuel quality. Coolant level. Are all checks OK?	Yes	Go to next step.
1		No	Service as required. Verify symptom no longer exists.
2	PERFORM PCM QUICK TEST See PCM QUICK TEST . Are any DTCs displayed during Continuous Memory Self-Tests, Key ON, Engine OFF (KOEO), Engine OFF (KOEO) or Key ON, Engine OFF (KOEO), Engine Running (KOER)?	Yes	Check for cause. See DIAGNOSTIC TROUBLE CODE NUMBERS .
2		No	Go to next step.
3	CHECK PIDS Connect WDS or equivalent tester. Check following PIDS. DPFE, ECT, IAC, LONGFT1, LONGFT2, VPWR. See PCM QUICK TEST . Are PIDS within specification?	Yes	Go to next step.
3		No	Service as required.
4	CHECK SECONDARY IGNITION SYSTEM Is strong blue spark visible at each disconnected high-tension lead while cranking engine?	Yes	Check spark plugs: If OK, go to next step. If not OK, clean or replace spark plugs. See IGNITION COIL-ON-PLUG AND SPARK PLUG -- 2.3L , or IGNITION COIL-ON-PLUG AND SPARK PLUG -- 3.0L (4V) .
4		No	Check following: High-tension leads. See TEST 15: IGNITION SCOPE TEST . CKP sensor. See CRANKSHAFT POSITION (CKP) SENSOR MALFUNCTION . CMP sensor. See CAMSHAFT POSITION SENSOR (CMP) MALFUNCTION .
5	CHECK FUEL DELIVERY SYSTEM Perform fuel pressure inspection. See TEST 9: FUEL LINE/FUEL PRESSURE HOLD INSPECTION . Fuel line pressure: 240-380 kPa (35-55 psi). Is fuel pressure correct?	Yes	Go to next step.
5		No	If pressure is greater than 380 kPa (55 psi): Replace fuel pump. See FUEL PUMP MODULE . If pressure is less than 240 kPa (35 psi): Check fuel supply line for restriction.
6	CHECK FUEL DELIVERY SYSTEM Check fuel pump fuel flow. See TEST 4: FUEL DELIVERY SYSTEM . Did fuel system flow the required amount of fuel?	Yes	Check injector for leakage. See TEST 10: FUEL INJECTOR INSPECTION . If injector leaks, service as necessary. See FUEL INJECTORS . If injector OK, go to next step.
6		No	Check fuel supply line for restriction.
7	CHECK EXHAUST SYSTEM Is there a restriction in the exhaust system?	Yes	Service as required.
7		No	Go to next step.
8	CHECK AUTOMATIC TRANSAXLE (A/T) If vehicle has manual transaxle, go to next step. If vehicle has automatic transaxle, go to TROUBLESHOOTING for Diagnostic Strategy. Is automatic transaxle OK?	Yes	Go to next step.
8		No	Service as required.
9	CHECK PCV SYSTEM Remove PCV valve and shake it. Does PCV valve rattle?	Yes	Install PCV valve. Go to next step.
9		No	Replace PCV valve. See POSITIVE CRANKCASE VENTILATION (PCV) VALVE -- 2.3L .
10	CHECK PCV SYSTEM Start engine and bring to normal operating temperature. Disconnect crankcase ventilation hose from throttle body. Place a stiff piece of paper over the hose. Wait one minute. Does vacuum hold paper in place?	Yes	Go to next step.
10		No	Disconnect evaporative hose. Place a stiff piece of paper over the hose. Wait one minute. Does vacuum hold paper in place? If yes, See EVAPORATIVE EMISSION (EVAP) SYSTEM MALFUNCTION . If no, check for vacuum leaks, obstructions in the PCV system, oil cap, PCV valve, rocker cover bolt torque/gasket leak. Service as required.
11	ADDITIONAL CHECKS Additional checks: Brake drag. Base engine concerns. Incorrect PCV valve. Contaminated MAF/IAT sensor. Cooling system. Are all checks OK?	Yes	Go to next step.
11		No	Repair as necessary. Verify a symptom no longer exists.
12	Verify test results. If OK, see DIAGNOSTIC INDEX to service any additional symptoms.