For 1990-2009 cars

#### Faulty Fuel Economy

Tests/Inspections | Action
--- | ---
DEFINITION: Fuel economy, as measured by an actual road test is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.
Preliminary |

• | Refer to Diagnostic System Check - Engine Controls .

• | Refer to Symptoms - Engine Controls .

• | Search for service bulletins.

• | Determine the customer's driving habits:

- | Is the A/C on all the time?

- | Is the defroster mode on?

- | Are the correct tire size and pressure used?

- | Are excessively heavy loads being carried?

- | Any heavy acceleration?

• | Inspect for dragging brakes. Refer to Diagnostic System Check - Hydraulic Brakes in Hydraulic Brakes.

Fuel System |

• | Test the fuel pressure. Refer to Fuel System Diagnosis .

• | Test the fuel injectors. Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

• | Test for a contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Ensure that each injector harness is connected to the correct injector. Refer to

#### Power, Ground, and Injectors

Master Electrical Component List
Powertrain Control Module Description
Engine Data Sensors
Power, Ground, KS, CMP, CKP Coils, and ICM
OBD II Symbol Description Notice
G103 and G105
Compressor Controls
IGN SW-BATT2, WIPER, AIR BAG, TURN LPS, IGN MOD, BU LMP, PCM IGN, F/PINJR, A/C BFC, AUTO TRANS, ABS, IGN Fuses
.

• | Inspect for fuel in the pressure regulator vacuum hose.

Sensor/System |

• | Test the oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicon or other contaminants from fuel, or the use of improper room temperature vulcanizing (RTV) sealant. The sensor may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage (rich exhaust indication). The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.

• | Test for correct operation of the manifold absolute pressure (MAP) sensor.

• | Test for correct operation of the throttle position (TP) sensor.

• | Test for correct operation of the engine coolant temperature (ECT) sensor.

• | Test for correct operation of the speedometer.

Ignition System |

• | Test for correct operation of the knock sensor (KS).

• | Test for the correct ignition voltage output with the J 36012-A spark plug jumper wires and J 26792 spark tester or equivalent.

• | Inspect the spark plugs for the following conditions:

- | Any wet or fuel fouled plugs

- | Any cracks

- | An incorrect gap

- | Any burnt electrodes or heavy deposits

- | The correct heat range.

• | If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

• | Inspect the ignition control module (ICM) for a correct ground connection.

• | Inspect the ignition coils for cracks or carbon tracking.

Cooling System |

• | Inspect for the correct coolant level.

• | Inspect for an incorrect or malfunctioning thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical |

• | Inspect for the following:

- | A low compression.

- | Refer to Engine Compression Test in Engine Mechanical.

- | Any broken valve springs.

- | Any sticking or leaking valves.

- | Any worn camshafts lobes.

- | An incorrect valve timing.

- | Refer to Symptoms - Engine Mechanical in Engine Mechanical.

- | Any excessive oil in combustion chamber and leaking valve seals.

- | Refer to Oil Consumption Diagnosis in Engine Mechanical.

• | Check for incorrect basic engine parts. Inspect the following:

- | The camshafts

- | The cylinder head

- | The pistons, etc.

- | Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional |

• | Test for the correct operation of the transaxle and the torque converter clutch (TCC). Refer to Road Test in Automatic Transaxle.

• | Inspect the exhaust system for air leaks before or near the O2S 1.

• | Inspect the exhaust system for the following conditions:

- | Any damaged or collapsed pipes

- | Any heat distress or internal failure of the muffler

- | A plugged 3-way catalytic converter. Refer to Restricted Exhaust in Engine Exhaust .