Poor Fuel Economy

DETECTION CONDITION AND POSSIBLE CAUSE

11	POOR FUEL ECONOMY
DESCRIPTION	FUEL ECONOMY UNSATISFACTORY

POOR FUEL ECONOMY INSPECTION

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. Transmission fluid level. Fuel quality. Coolant level. Are all checks OK?	Yes	Go to step 2.
1		No	Service as required. Verify symptom no longer exists.
2	PERFORM PCM QUICK TEST Are any DTCs displayed during Continuous Memory Self Tests, Key ON, Engine OFF (KOEO) or Key ON, Engine Running (KOER)?	Yes	Check for cause, See DIAGNOSTIC TROUBLE CODE NUMBERS .
2		No	Go to step 9.
3	CHECK PIDS Connect NGS Tester. Check following PIDS. DPFEGR, ECT, IAC, LONGFT1, LONGFT2, VPWR. Are PIDS within specification? See PIN VOLTAGE/PID VALUE CHARTS article .	Yes	Go to step 4.
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 step 5. If not OK, clean or replace spark plugs,
4		No	Check following: High-tension leads, see TEST 17: IGNITION SCOPE TEST . CKP sensor. See TEST 8: CRANKSHAFT POSITION (CKP) SENSOR . CMP sensor. See CAMSHAFT POSITION (CMP) SENSOR MALFUNCTION .
5	CHECK FUEL DELIVERY SYSTEM Perform fuel pressure INSPECTION, See TEST 11: FUEL LINE PRESSURE / FUEL PRESSURE HOLD INSPECTION . Is fuel pressure correct? Fuel line pressure: 386-496 kPa (56-72 psi), 3.0L flexible fuel 380-517 kPa (55-75 psi).	Yes	Go to step 6.
5		No	If pressure is greater than 496 kPa (72 psi), 3.0L flexible fuel 517 kPa (75 psi): Replace fuel pump, See FUEL PUMP in REMOVAL, OVER HAUL, & INSTALLATION article in Engine Performance . If pressure is less than 386 kPa (56 psi), 3.0L flexible fuel 380 kPa (55 psi): Check fuel supply line for restriction.
6	CHECK FUEL DELIVERY SYSTEM Check fuel pump fuel flow. See TEST 5: FUEL DELIVERY SYSTEM . Did fuel system flow the required amount of fuel?	Yes	Check injector for leakage. See TEST 12: FUEL INJECTOR INSPECTION . If injector leaks, service as necessary. FUEL RAILS & INJECTORS in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance . 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 step 8.
8	CHECK AUTOMATIC TRANSMISSION (A/T) If vehicle has manual transmission, go to step 9. See DIAGNOSIS - 4R44E or DIAGNOSIS - 5R55E for automatic transmission concerns. Is automatic transmission OK?	Yes	Go to step 9.
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 step 10.
9		No	Replace PCV valve,
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 step 11.
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 step 9. 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 sensor. Cooling system. Are all checks OK?	Yes	Go to step 12.
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