Basic Emission Control Systems and What They Do Automotive-generated pollutants come from three sources: tailpipe, crankcase blowby vapors and fuel vapors that evaporate from the fuel tank and carburetor. Crankcase blowby vapors are eliminated as a source of pollution by recirculating the vapors into the engine for reburning through the Positive Crankcase Ventilation (PCV) system. The PCV valve acts like a small calibrated vacuum leak, allowing manifold vacuum to siphon air through the crankcase, taking with it moisture and blowby gases that would otherwise pollute the atmosphere. As a side benefit, it extends motor oil life. Evaporative emissions have been eliminated by sealing the fuel system and storing vapors in a charcoal canister. When the engine starts, a purge valve on the canister opens, allowing manifold vacuum to siphon vapors into the intake manifold to be burned in the engine. There are 3 primary tail pipe pollutants: Carbon monoxide (CO) is formed whenever there is not enough oxygen to completely burn the fuel. The richer the mixture, the greater the quantity of CO produced. Carbon monoxide is the worst pollutant of the three because it is deadly. CO emissions are reduced by keeping the air/fuel ratio lean, by preheating incoming air and manifold to aid fuel vaporization, and by converting the remaining CO into harmless carbon dioxide in the catalytic converter. Hydrocarbon (HC) emissions are unburned gasoline. HC is not directly harmful, but it contributes to smog formation. A fouled spark plug, a leaky exhaust valve, or a fuel mixture so lean it won’t ignite (lean misfire) can all allow unburned fuel to enter the exhaust. HC is reduced by maintaining a balanced air/fuel mixture, by making sure compression and ignition are OK, and by reburning any HC remaining in the catalytic converter. Oxides of Nitrogen (NOX) are formed in the combustion chamber when temperatures rise above 2,500 degrees F and nitrogen begins to react with oxygen. Lean air/fuel mixtures burn hotter and increase NOX. Though not as poisonous as carbon monoxide, NOX irritates the eyes, nose and lungs, and contributes to ozone depletion and acid rain formation. Exhaust Gas Recirculation (EGR) Valve NOX is reduced by the Exhaust Gas Recirculation (EGR) system, and catalytic converter(s). The EGR system allows a small amount of exhaust gas to be siphoned back into the intake manifold to slightly dilute the incoming air/fuel mixture. This lowers combustion temperatures to reduce NOX. It helps prevent detonation. The catalytic converter contains a ceramic honeycomb or ceramic pellets coated with a thin layer of platinum and palladium metal. In three-way converters, a third catalyst (rhodium) is included to reduce NOX. The converter acts to reburn pollutants. To do so, it needs extra oxygen received from an air pump or an aspirator valve. Arrows show air flow through the system. Air travels from the air filter to each cylinder where it mixes with hydrocarbons and carbon monoxide and then escapes into the atmosphere through the exhaust system. The air pump is belt-driven and feeds air to the exhaust manifold through a diverter valve and check valve. The diverter valve dumps excess air back into the atmosphere when it’s not needed (during deceleration, for example). On some engines, a gulp valve is another part of the plumbing. The gulp valve diverts air from the pump into the intake manifold. This momentarily leans out the mixture during deceleration, preventing backfiring in the exhaust from too much fuel. On some engines, an aspirator is used in place of an air pump. An aspirator is a one-way valve that allows air to be siphoned into the exhaust system between exhaust pulses. When computerized engine controls and three-way catalytic converters were added, the air pump gained yet another control valve. When the engine is cold, air is routed to the exhaust manifold to help reduce the initial HC and CO emissions. NOX is not a problem when the engine is cold. As the engine warms up and NOX starts to rise, the flow of air is diverted from the exhaust manifold directly to the converter where it enters a chamber between the two catalysts. Copyright © 1999, ALLDATA email@example.com
FIXING YOUR PRESENT VEHICLE SAVES MONEY
Most of us want to get the most for our motoring dollar. One of the best ways to do this is extending the life of your current vehicle. With new car prices in the United States averaging well over $ 10,000, money invested in keeping your existing vehicle in good shape could save you hundreds–even thousands–of dollars a year. When you consider the true cost of buying a new car (price of the car, sales tax, license, and registration fees, insurance), it is not difficult to justify investing a few hundred dollars to repair your present vehicle.
SAFETY AND SCHEDULED MAINTENANCE
The safety aspect of properly maintaining your vehicle, especially when it has high mileage, should not be overlooked. Failing brakes, exhaust leaks and other problems can be prevented by following sound car care practices.
Unfortunately, most manufacturers only provide maintenance guidelines for the first 100,000 miles or so. Clear procedures for maintenance beyond this mileage do not exist. At best, manufacturers provide interval service schedules, such as every 15,000 miles. These schedules should be followed whenever possible. By doing so, you can reasonably expect thousands more satisfactory miles from your vehicle.
HIGH MILEAGE INSPECTION AND EVALUATION
If your vehicle has passed the 100,000 mile mark and you want to significantly prolong its useful life, it is time to have it thoroughly evaluated by a professional automotive technician who can recommend needed repairs or service. This facility is equipped to perform this service. We employ technicians who use factory-level information detailing your vehicle’s service requirements.
Our high mileage inspection and evaluation goes beyond cursory “once-overs” and is designed to get to the root of potential problems. Ask your service advisor or technician to show you exactly what is involved in this service. He or she will be happy to go over the evaluation form with you before you okay the inspection and provide you with a comprehensive estimate for any work recommended as a result of your vehicle’s checkup. They will tell you about repairs that are necessary today, and also alert you to items that are potential problem areas you may want to address today for more trouble-free miles tomorrow. Naturally, you make the decision as to what work is actually performed.
Working together, we can add years to the life of your car or truck.
Copyright © 1999, ALLDATA 1-800-859-3282 3.30
Disuse is the enemy of all automobiles. In truth, a car driven a thousand miles a week doesn’t need as much maintenance and frequently will require fewer repairs than the car that’s only driven a couple thousand miles in an entire year. On newer cars, seals and gaskets are not the major problem. Modem technology has given us sealing components capable of withstanding long periods of disuse with little or no adverse effects.
The really insidious damage to an engine, be it new, old, or in-between, stems from fluids contaminated by acid and moisture. Controlling acids in the crankcase is easy to do. It amounts to nothing more than changing the oil immediately prior to storage. However, there is a rule which states that engine operation should be limited to a maximum of 15 (fifteen) minutes after the oil change. Running the engine for more than that negates the benefits. Running an engine even for short periods of time will cause minor to major oil contamination from combustion by-products.
The combustion of fuel and air in the cylinders of any engine is relatively inefficient. It leaves carbon, unburned fuel, moisture, and a host of other unfriendly things, which contaminate the oil. In day to day operation those by-products are dissipated through engine heat and evaporation. But, during long-term disuse contaminated oil will remain between the crankshaft and the crankshaft bearings, and the camshaft and the camshaft bearings, etc. Because some of the contaminates will be acidic and because bearing material is very soft, bearing etching is probable. This does not lead to immediate or catastrophic failure, but rather to shortened engine life.
Oil contamination is certainly a problem, but the really bad actor is . . . water. Not just water in the oil either, but water that forms in the cylinders as a result of condensation. As temperatures fluctuate from night to day, the cylinder walls sweat. The resulting moisture trickles down the cylinders to the lower sides of the pistons. Left untreated, condensation causes pitted cylinder walls, and corroded pistons and piston rings, a potentially deadly condition.
Your assignment, should you decide to take it, is to control moisture, control acid, and control corrosion. If the vehicle is going to be stored more than 30 days, in anything less than a temperature controlled garage, you should follow a rigid storage procedure:
Wash your car in detail. Be particularly careful to remove all dirt and other foreign material from under the car, from behind moldings, and especially around the front and rear windshields.
Every interior surface should also be cleaned exceptionally well. Vacuum not only the carpeting and seats, but under the seats and mats. Remove the rear seat cushion and clean this area. All surfaces, door panels, dash, steering wheel, kick panels, etc., should be dust-free and protected with an appropriate chemical.
Apply a heavy coat of high quality wax to the exterior.
Using silicone, spray all rubber items, including bushings and hangers under the car. All weather-stripping should be treated with silicone and don’t forget the weather-strip under the trunk lid.
Spray hinges and latches with white lithium grease. Remember the trunk and hood hinges and their latches.
Test the pH level and visual clarity of the cars’ anti-freeze. The pH should be around 10. If it’s 11 or above, corrosion will occur because the coolant is too alkaline. If the pH is 9 or below, corrosion will occur from the coolant being too acidic. Either way, you lose! The ideal is to flush the cooling system and install fresh anti-freeze of the proper type and quantity. Add a coolant additive to prevent corrosion.
With the engine thoroughly warmed, change the engine oil and oil filter, using oil of the recommended quality and viscosity.
Unless it’s been done in the last 6 to 9 months, flush the brake system, using fresh DOT 4 Brake Fluid from an unsealed container. If the vehicle has a hydraulic clutch, flush this system using appropriate fluid (usually brake fluid).
Change transmission fluid and filter in an automatic transmission, unless it’s been done in the last year.
Here’s the really critical part. Disable the ignition system so no high voltage can be generated. Remove the spark plugs from the cooled engine; spray about two tablespoons of Liquid Wrench or similar product through the spark plug holes. Once that’s done, crank the engine for 15 seconds, the ignition system is still disconnected.
Now it’s time to inject about two (2) tablespoons of engine oil into each cylinder and once more crank the engine for 10 to 15 seconds. This helps reduce the possibility of moisture forming and it keeps any moisture that does form, from attacking the metal. The spark plugs and spark plug wires can be reinstalled once all this is done, but DO NOT start/run the engine as this will undo all the protection you’ve just provided.
Also I forgot to mention the fuel tank should be full, and the fuel in the tank should be treated with a stabilizer such as Stor-N-Start. Run the car for 10 to 15 minutes so the stabilized fuel will be dispersed throughout the fuel system to prevent gasoline breakdown. Stor-N-Start is available at farm supply stores, and at RV and marine supply outlets.
The friendliest way to treat tires and suspension parts is to place the car in its temporary place, adjust tire pressure to the recommended inflation, and jack the car up. Next, support the car with jack stands placed as close to the inside of each tire as possible. Proper positioning of the jack stands is crucial because the springs must be pre-loaded, not hanging free. It isn’t unusual for spring rates to change when stored for long periods of time without a pre-load.
Best battery life requires that you disconnect the battery and install a 100%-fully-automatic-total-shut-off trickle charger.
A high quality, breathable car cover is essential. If the car is stored indoors there must be no electric motors or other electrical devices that produce ozone. Ozone causes rapid deterioration of rubber items.
And don’t forget your vehicle’s fuzzy neighbors; squirrels, mice, rats, and even an occasional cat. Field mice for instance are extremely classy critters. They love to build a nest in the wire harness or in the front seat of a Corvette. Guess that shows it isn’t just large mammals who appreciate the finer things in the automotive kingdom.
If you’re looking for car covers or a complete enclosure for weather protection or for rodent control, contact:
B & W, Inc.
PO Box 106
Hunt Valley, MN 56219
‘Mid-America Designs’ also offers covers and enclosures, 800-500-VETT.
Tell the Customer Service Rep, at B & W or Mid America, I said Hello.
The possible consequences of not following storage procedures could be horrific.
WHY PREVENTIVE MAINTENANCE?
Manufacturers know that a properly maintained car will be more dependable, safer, last longer, and increase your satisfaction with their product. Car makers and owners also have a responsibility to make sure emission controls receive regular service and are functioning properly. Regular maintenance helps accomplish these goals by keeping your engine running efficiently and eliminating potential problems that may leave you stranded.
WHAT’S IN IT FOR YOU?
A More Dependable Car
A car that retains the “new car feel”
Less chance of a costly breakdown
A safer car for you and your family
Doing your part for cleaner air
A car worth more at trade in or sale
An intact warranty
When it comes to automobiles, safety and reliability are the two most important factors for most of us. This is especially true now that spring has arrived and we start planning for summer trips. Some preplanning can lead to peaceful, safe trips. Many people, however, have no idea what to check and what to replace on their car to make this happen. So let’s walk through the process.
Winter always takes a toll on our cars but this past winter has been worse than any I can remember. The ice and cold were brutal which means more things need to be checked and to be checked more carefully than usual.
To assure safe operation start by checking the brake system. This will include having a technician test the brake fluid for moisture content. The test is performed with a tester, which is immersed in the brake fluid at the master cylinder. Using electronic circuitry it measures the percent of moisture in the fluid. If the fluid fails, it will be necessary to flush the brake hydraulic system and install new brake fluid. This operation is vital to safety because excessive moisture can boil during a panic stop leading to momentary brake loss. If you really want the best for your car and yourself, have the brake system flushed once every year.
Next is the physical measurement of the brake pads and shoes as well as a thorough check of the hydraulic parts. Have your technician pay particular attention to the steel brake lines and rubber brake hoses which may have been damaged as a result of the extreme quantities of salt used this winter.
The tires need to be carefully checked for proper wear and pressure. Check the tire sidewalls and tread for signs of cuts that may be the result of ice damage. If the tires haven’t been rotated for a while now is a good time. Have the tires rotated every 6,000 miles to get the best tire wear.
Constant velocity joint boots should be carefully inspected for damage. I’m seeing many damaged boots this year as a result of the ice.
Axle and wheel bearings need to be looked at; again ice and salt may have taken a toll.
Inspection of the exhaust system is definitely recommended. It’s a common misconception that you need to be more careful of exhaust fumes in the winter than in the summer. That was correct before the advent of auto air conditioning because we used to drive with the windows rolled down for ventilation. Today most of us ride with the windows rolled up and the air conditioning turned on which means an exhaust leak can be deadly in the summer too.
Check all lights for proper operation. You should get in the habit of turning the lights on and walking around the car before driving. Only under safe conditions of course!
The car should be run over a “scuff’ gauge to determine if the front end is out of alignment. This is the quickest least expensive way to check alignment.
Fuel lines, hoses and filters need to be looked at. Many late model cars use metal or plastic fuel lines and fuel line fittings which can he damaged by ice and road salt.
The cooling system should be pressure tested for leaks. Check the condition of the radiator hoses, heater hoses and fan belts. These rubber parts typically have a usable safe life expectancy of four years or fifty thousand miles. Have your technician check the pH level of the coolant in your radiator too. The pH should be no lower than 9 if it is have the cooling system flushed and new coolant installed immediately. I recommend yearly flushing of the cooling system to prevent expensive damage.
The battery is another area of concern during hot weather. I recommend you have a heavy load test performed on the battery, which will give you a good idea as to its general condition. Be sure the battery cable connections are clean and tight and are coated with a corrosion preventer. If your battery is at or very near the end of its warranty period, replace it! Most battery manufacturers have a good idea how long their product will last and guess what? It’s usually about to the end of the warranty.
Check the items related to performance. This is best done by having a good technician hook up a diagnostic tester and run the full test on your engine. This will disclose the condition of parts like spark plugs, spark plug wires, distributor cap, distributor rotor, fuel injectors or carburetor plus many other important parts. Look for a highly qualified technician or the results may be marginal. Always select technicians who are ASE certified. In this case the technician should have an ASE engine performance certificate.
A scan of your cars computer system is also a good idea. The scan is easy and inexpensive and will tell the technician if there are any fault codes stored in the computer’s memory. The scan procedure will also let the technician know about the operating condition of the computer sensors. Critical: there is no such thing as a fault code that tells what part is defective it only tells the technician what diagnostic procedure to follow.
Last is a general check of small items such as windshield wiper blades, washer fluid, transmission fluid, etc.
Lubrication of the door weather-stripping will make your car much more enjoyable to drive. It does away with those annoying squeaks that emanate from dry rubber. Use high quality spray silicone from your auto parts store.
By following a good preventive maintenance schedule you will avoid most of those annoying highway problems.
Copyright 05/94 Pat Goss all rights reserved
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.
DRIVE SAFE DRIVE SMART!
Copyright 04/1994 Pat Goss all rights reserved
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
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.