Engine - Fuel Economy Service Tips

90ford06

Article No. 90-6-15

FUEL ECONOMY - 4.9L, 5.0L AND 5.8L ENGINES - SERVICE TIPS

LIGHT TRUCK: 1985-90 BRONCO, E SERIES, F SERIES

ISSUE: Fuel economy, considered unsatisfactory by some customers, may be due to a lack of customer awareness of various conditions that can unfavorably affect fuel economy.

ACTION: Use the following sections to assist in diagnosing complaints of low fuel economy. Refer to the Engine/Emission Diagnosis Manual for additional diagnostic information.

CUSTOMER INTERVIEW

1. Determine how the fuel economy is being calculated.

NOTE: SOME CUSTOMERS USE OUT OF POCKET COST AS A BASIS TO MEASURE FUEL ECONOMY RATHER THAN ACTUAL CALCULATION OF MPG.

Two tanks of fuel are usually needed to accurately calculate fuel economy. Canadian fuel economy is calculated with the following formula:

Kilometers Traveled/Liters Used x 2.819 - Miles/imperial Gallons

2. Ask the customer to describe their driving habits. See the conditions below that decrease fuel economy:

^ Stop and go city driving is 17% less efficient than steady highway driving

^ Short trips of 3 miles or less increase fuel usage due to lower engine operating temperatures

^ A loss of fuel economy due to an increase in posted speed limits or operating avehicle at higher than posted speeds. Test results indicate a loss of about 2.4 MPG for every 10 MPH increase above 40 MPH

^ Hilly or mountainous terrain requires more power from the engine to maintain a constant speed thus demanding more fuel

^ Use of speed control in hilly and mountainous terrain

^ Idling for long periods can consume about 0.7 gallons of fuel per hour

^ Vehicles frequently loaded down or used to pull a trailer. Fuel economy decreases due to the increase in total weight and frontal area.

VEHICLE INSPECTION

1. Tire pressure should be set at the vehicle manufacturer's specification. Under inflated tires have a higher rolling resistance which requires more power to roll. Under inflated tires can reduce fuel economy by as much as 1 MPG.

2. Bug deflectors, running boards, and sun shields affect fuel economy. Each item affects fuel economy by 1-2 MPG. The faster the vehicle is operated, the greater the effect.

3. Look for vacuum leaks and restrictions. Pay particular attention to the MAP and EGR vacuum lines.
4. Look for electrical concerns such as broken, chafed or disconnected wires. Examples of areas to check are:

^ Electrical grounds must have good continuity (0.4 omhs or less with the battery positive cable and the EEC processor disconnected).

^ Battery cables must be clean and free of corrosion

^ Non-factory items such as two-way radios, electric trailer brakes and mobile telephones must have the wiring at least 5 cm away from any factory electronics.

NOTE: ELECTRICAL POWER FOR NON-FACTORY ITEMS SHOULD BE TAKEN DIRECTLY FROM THE BATTERY OR FUSE PANEL. THE SHORTEST POSSIBLE ROUTE IS RECOMMENDED.

5. Ignition timing, including spark advance, should be checked to make sure it is within specification.

6. The speedometer/odometer calibration could be inaccurate due to aftermarket tires that are oversize. Oversize tires will cause the speedometer to indicate lower than actual vehicle speed. They also cause the odometer to indicate less than actual miles traveled which could appear as a 10% reduction in fuel economy.

FUEL OUALITY

Fuel quality can be checked for water, alcohol, lead, and fuel vapor pressure using Rotunda Gas Check Test Kit 113-00004. These items can cause poor fuel economy.
Lead in fuel has the following effect:
^ Contaminates the EGO sensor causing inaccurate reading to the processor. This results in an over-rich fuel condition.

^ Catalytic converter may overheat and plug, creating high exhaust back pressure.

Alcohol in fuel has the following effect:

^ Incomplete combustion because alcohol does not burn as hot as gasoline.

If fuel quality is poor, the fuel should be replaced before proceeding. The catalytic converter and EGO sensor may require attention also.

BOTTLE TEST

A bottle test may be the only way to resolve a fuel economy concern.

^ Using Rotunda Mileage Tester 021-00042, bottle test the vehicle at a steady speed of 60 MPH over the same section of road in both directions.

^ Repeat the test as necessary for consistency.

^ Average the results to account for normal test-to-test variations such as hills and wind.

NOTE: IF THE FUEL ECONOMY IS NOT SATISFACTORY, REFER TO THE ENGINE/EMISSIONS DIAGNOSIS MANUAL FOR FURTHER ACTION.

OTHER APPLICABLE ARTICLES: none
SUPERSEDES: 88-26-14
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 4500, 640200