Replacing your Auto A/C Compressor?

Replacing your auto A/C Compressor?
If you are replacing your A/C Compressor or need to understand
what the service shop is talking about, this article will provide you
the complete details and what’s really required to do the job right!

What Effects Fuel Economy on Newer Cars?

Better fuel economy on newer cars.

As cars have evolved they have become much more fuel efficient, but they are also influenced by many more outside factors. With this in mind how does one maintain an automobile so it will deliver its best fuel economy?

The answer to that question is, keep the basics under control! Start with the most basic item, tire pressure. To check tire pressure the tires must be cold. For tires to be considered cold the car could not be driven more than three miles in the last eight hours. Cold tires are the most important part of checking pressure. As you drive friction causes the tires to heat up resulting in a corresponding increase in tire pressure as there is no rating for hot tire pressure the check must be done when the tires are cold. For accurate pressure readings, a quality gauge is necessary; one of Consumer Reports top rated tire gauges is your best bet.

It’s important to know, proper tire pressure is not stamped on the tire. Also, there is no such thing as a generic tire pressure. To get it right, look at your owner’s manual. Your manual will tell you where to look for the decal that shows proper tire size, inflation information and load ratings.

Another system affecting gas mileage is wheel alignment. Improper alignment can decrease fuel economy by as much as 5 miles per gallon. Note: wheel alignment applies to the rear wheels as well as the front so have both rear and front checked.

Oxygenated fuel can decrease fuel economy by as much as 1 mile per gallon. This applies to cars that normally deliver 25-30 miles per gallon on 100% gasoline (NON-OXYGENATED). Higher mileage cars may experience a greater decrease and more thirsty cars may decrease less. Using higher than recommended octane gasoline will not improve fuel economy.

Routinely driving on rough roads will decrease fuel economy. Gravel, dirt, badly rutted roads with rough surfaces, or potholes cause gas mileage to drop. Sometimes significantly!

Tire type and profile can have a big effect on fuel usage. When buying new tires be wary of the salesperson who recommends a different tire profile. You may encounter a salesperson who will say a high performance tire is better than a standard profile tire. This may be true from the standpoint of handling (you will be able to go around corners faster) but you will almost always use more gas, because lower wider tires offer more resistance to rolling. Changing from a 75 series tire to a 60 series low profile high performance tire can cost up to 3 miles per gallon of gas. Higher profile tires may create confusion about gas mileage because they turn fewer revolutions per mile resulting in an odometer error. What appears to be a decrease in mileage may in reality be a slight improvement. For best gas mileage, safety, and overall performance I recommend you buy tires that match all original specifications.

The use of air conditioning will cause a decrease in gas mileage but this may be the lesser of the evils. When you turn the a/c off and roll down the windows you will probably double your economy loss. This is because lowering a car’s windows changes its aerodynamics. Modern cars are designed to move freely through the air. When you open a window the car no longer moves as freely causing the engine to work harder and consume more fuel. These same factors explain why add-on roof racks, luggage strapped to the roof or an open trunk lid will also cost you mileage.

Not using overdrive at highway speeds may decrease your mileage by 3 to 5 miles per gallon. If you are the type person who rides with your foot resting lightly on the brake pedal you will definitely pay. This horrible habit may cause as much as 7 miles per gallon lower mileage than proper driving. Riding the brake pedal results in the brakes being very lightly applied. You may not feel this but it does cause the engine to work harder. In addition to the extra strain placed on the engine a lightly applied brake may disengage the transmission torque converter clutch which further reduces mileage. It also causes lots of expensive wear to the brakes.

For those of you who add electrical gadgets to your car expect to lose 4/10 mile per gallon for each ten amps of electrical energy consumed. Add a set of fog lamps and a radio that each consume 10 amps and expect to lose nearly one mile per gallon.

That toolbox and those bags of sand in the trunk will cost you to the tune of 3/10 mile per gallon for every 125 pounds of added weight. For good gas mileage tighten your load as much as possible.

Always perform all maintenance as required in your owner’s manual. A properly maintained car will give better fuel economy for a longer time. Remember also whenever you experience a noticeable sudden decrease in fuel economy the first thing to check is the engine cooling system thermostat. Today’s cars are equipped with onboard computers that rely on the temperature of the coolant to determine how much fuel should be delivered to the engine. A stuck thermostat can cause the engine to run much colder than normal resulting in up to 8 miles per gallon less fuel mileage.

Last but not least if you love the feel of raw power during acceleration and spend lots of time with your right foot on the floorboard expect a fuel economy penalty up to 15 miles per gallon. This holds true for highway driving also as higher speed automatically means lower gas mileage. Consider this, it takes 15% more fuel to drive 65 mph than to drive 55 mph. The difference gets worse as the speed increases.


Copyright 04/1994 Pat Goss all rights reserved

Which Engine Sensors Are the Most Important?

Which Engine Sensors Are the Most Important?

Typical Components Of A Late-Model Ford EEC-IV System

All sensors are important. The computer is the brains of a computerized engine control system and sensors are its link to what’s happening under the hood.

Some sensors have more influence on engine performance than others. These include the coolant temperature sensor, oxygen sensor, throttle position sensor, and manifold absolute pressure sensor.

The coolant sensor is often called the master sensor because the computer uses its input to regulate many other functions, including:

Activating and deactivating the Early Fuel Evaporation (EFE) system such as the electric heating grid under carburetor or the thermactor air system.

Open/closed loop feedback control of the air/fuel mixture. The system won’t go into closed loop until the engine is warm.

Start up fuel enrichment on fuel-injected engines, which the computer varies according to whether the engine is warm or cold.

Spark advance and retard. Spark advance is often limited until the engine reaches normal operating temperature.

EGR flow, which is blocked while the engine is cold to improve driveability.

Canister purge, which does not occur until the engine is warm.

Throttle kicker or idle speed.

Transmission torque converter clutch lockup.

Cut-A-Way View Of A Coolant Sensor

The coolant sensor is usually located on the head or intake manifold where it screws into the water jacket. Sensors come in two basic varieties: variable resistor sensors called thermistors because their electrical resistance changes with temperature, and on/off switches, which work like a conventional temperature sending unit or electric cooling fan thermostat by closing or opening at a preset temperature.

Variable resistor coolant sensors provide the computer with a more accurate indication of actual engine temperature than a simple temperature switch. The computer feeds the sensor a fixed reference voltage of about five volts when the key is on.

The resistance in the sensor is high when cold and drops about 300 ohms for every degree Fahrenheit as the sensor warms up. This alters the return voltage signal back to the computer which the computer then reads to determine engine temperature.

The switch-type sensor may be designed to remain closed within a certain temperature range, or to open only when the engine is warm. Switch-type coolant sensors can be found on GM “T” car minimum function systems, Ford MCU, and Chrysler Lean Bum systems.

Because of the coolant sensor’s central role in triggering many engine functions, a faulty sensor (or sensor circuit) can cause a variety of cold performance problems. The most common symptom is failure of the system to go into closed loop once the engine is wan-n. Other symptoms include poor cold idle, stalling, cold hesitation or stumble, and/or poor fuel mileage.

The oxygen sensor (02) measures how much unburned oxygen is in the exhaust. The computer uses this as an indication of how rich or lean the fuel mixture is so adjustments can be made to keep it properly balanced.

A problem with the 02 sensor will prevent the computer from keeping the fuel mixture balanced under changing driving conditions, allowing the mixture to run rich or lean.

The throttle position sensor (TPS) is used with feedback carburetion and electronic fuel injection (EFI) to inform the computer about the rate of throttle opening and relative throttle position. A separate idle switch and/or wide open throttle (WOT) switch may also be used to signal the computer when these throttle positions exist.

The throttle position sensor may be mounted externally on the throttle shaft (the case on most fuel injection throttle bodies), or internally in the carburetor (as in Rochester Varajet, Dualjet, and Quadrajet).

The TPS is essentially a variable resistor that changes resistance as the throttle opens. It is the electronic equivalent of a mechanical accelerator pump. By signaling the computer when the throttle opens, the computer enriches the fuel mixture to maintain proper air/fuel ratio.

Initial TPS setting is critical because the voltage signal the computer receives tells it the exact position of the throttle. Initial adjustment must be set as close as possible to factory specs. Most specs are given to the nearest hundredth of a volt.

The classic symptom of a defective or misadjusted TPS is hesitation or stumble during acceleration. The fuel mixture leans out because the computer doesn’t receive the right signal telling it to add fuel as the throttle opens. The oxygen sensor feedback circuit will eventually provide the necessary information, but not quickly enough to prevent the engine from stumbling.

When the sensor is replaced, it must be adjusted to the specified reference voltage. The TPS on most remanufactured carburetors is preset at the factory to an average setting for the majority of applications the carburetor fits. Even so, the TPS should be reset to the specific application upon which it is installed.

Ford And Delco Sensors

MAP sensor function is to sense air pressure or vacuum in the intake manifold. The computer uses this input as an indication of engine load when adjusting air/fuel mixture and spark timing. Computerized engine control systems that do not use a MAP sensor rely on throttle position and air sensor input to determine engine load.

Under low-load, high-vacuum conditions, the computer leans the fuel mixture and advances spark tinting for better fuel economy. Under high-load, low-vacuum conditions (turbo boost, for example); the computer enriches the fuel mixture and retards timing to prevent detonation.

The MAP sensor serves as the electronic equivalent of both a distributor vacuum advance diaphragm and a carburetor power valve.

The MAP sensor reads vacuum and pressure through a hose connected to the intake manifold. A pressure sensitive ceramic or silicon element and electronic circuit in the sensor generates a voltage signal that changes in direct proportion to pressure.

MAP sensors should not be confused with VAC (Vacuum) sensors, DPS (Differential Pressure sensors), or BARO or BP (Barometric Pressure) sensors. A vacuum sensor (same as a differential pressure sensor) reads the difference between manifold vacuum and atmospheric pressure (the difference in air pressure above and below the throttle plate). A VAC sensor is sometimes used instead of a MAP sensor to sense engine load.

A MAP sensor measures manifold air pressure against a precalibrated absolute (reference) pressure. What’s the difference? A vacuum sensor only reads the difference in pressure, not absolute pressure, so it doesn’t take into account changes in barometric (atmospheric) pressure.

A separate BARO sensor is usually needed with a vacuum sensor to compensate for changes in altitude and barometric pressure. Some early Ford EEC-111 and EEC-IV systems have a combination barometric pressure/MAP sensor called a BMAP sensor, combining both functions.

Anything interfering with accurate sensor input can upset both fuel mixture and ignition timing. Problems with the MAP sensor itself, grounds or opens in the sensor wiring circuit, and/or vacuum leaks in the intake manifold.

Typical driveability symptoms include detonation due to too much spark advance and a lean fuel ratio, and loss of power and/or fuel economy due to retarded timing and an excessively rich fuel ratio.

A vacuum leak can cause a MAP sensor to indicate low manifold vacuum, causing the computer to think the engine is under more load than it really is. Consequently, timing is retarded and the fuel mixture is enriched.

Copyright 1999, ALLDATA 1-800-859-3282 3.30

What should be included in a complete brake job?

A complete brake job should restore the vehicle’s brake system and braking performance to good-as-new condition. Anything less would be an incomplete brake job.

Brake components that should be replaced will obviously depend upon the age, mileage and wear. There is no pat answer as to which items need replacing and which ones don’t,every vehicle is different, they all must be checked.

Seven-Inch Rear Drum Brake Assembly

A complete brake job should begin with a thorough inspection of the entire brake system; lining condition, rotors and drums, calipers and wheel cylinders, brake hardware, hoses, lines, and master cylinder.

Any hoses that are found to be age cracked, chaffed, swollen, or leaking must be replaced. Make sure the replacement hose has the same type of end fittings (double-flared or ISO) as the original. Don’t intermix fitting types.

Steel lines that are leaking, kinked, badly corroded, or damaged must also be replaced. For steel brake lines, use only approved steel tubing with double-flared or ISO flare ends.

A leaking caliper or wheel cylinder needs to be rebuilt or replaced. The same applies to a caliper that is frozen (look for uneven pad wear), damaged, or badly corroded.

Leaks at the master cylinder or a brake pedal that gradually sinks to the floor tells you that the master cylinder needs replacing. The rotors and drums need to be inspected for wear, heat cracks, warpage, or other damage. Unless they are in perfect condition, they should always be resurfaced before new linings are installed. If worn too thin, replace them.

Rust, heat, and age have a detrimental effect on many hardware components. It’s a good idea to replace some of these parts when the brakes are relined. On disc brakes, new mounting pins and bushings are recommended for floating-style calipers. High temperature synthetic or silicone brake grease (never ordinary chassis grease) should be used to lubricate caliper pins and caliper contact points.

On drum brakes: shoe retaining clips and return springs should be replaced. Self-adjusters should be replaced if they are corroded or frozen. Use brake grease to lubricate self-adjusters and raised points on brake backing plates where shoes make contact.

Wheel bearings should be part of a complete brake job on most rear-wheel drive vehicles and some front-wheel drive cars. Unless bearings are sealed, they need to be cleaned, inspected, repacked with wheel bearing grease (new grease seals are a must), and properly adjusted.

As a rule, tapered roller bearings are not preloaded. Finger tight is usually recommended. Ball wheel bearings usually require preloading.

As a final step, old brake fluid should always be replaced with fresh fluid.