₦airaland Forum

depending on where the leak is coming from if its from the seal near the timing belt area belt could snap or skip causing costly damage to engine, the leak if coming from a worn out seal could deteriorate at a moments notice and cause costly damage to the engine there's no such thing as "if you are careful and observant when it comes to engine oil leaks" find the source and get it fixed or park the car.

For more tips on your car click this link https://www.nairaland.com/1788778/maintenance-tips-cars-quick-response#24358753

Re-occuring fuel pump issues

Fuel Tanks
All too often, vehicles are refueled from a badly rusted or dirt-contaminated fuel tank and in some case water contaminated also, finely granulated dirt will be filtered out in the fuel filter but, in most cases, larger granulations of dirt will clog the filter screen attached to the fuel pump inlet and starve the pump for fuel.
Whenever a fuel pump is replaced, the tank should be inspected for dirt contamination, for loose fuel pump baffling, and for dents or distortions that can restrict fuel entry into the fuel pump or fuel exit from the pressure regulator return line. In some cases, a fuel tank can be cleaned with a hot solution of water and detergent, but in other cases, it’s more cost-effective to replace the fuel tank. If the plastic anti-sloshing baffles have become dislodged from the fuel tank itself, the tank should be replaced with one of the many available from OE or aftermarket sources.
 
Low Fuel Level Effects (reserve/empty)

If you are one who appears to have more than his share of fuel pump failures, it’s a good bet that you are running your fuel tank nearly dry before refueling your vehicle. Even with adequate baffling in the fuel tank, low fuel levels tend to cause the fuel pump to ingest air during acceleration, cornering, and braking. Since modern high-speed fuel pumps require gasoline to lubricate the pump bearings and cool the pump itself, it’s cheaper in the long run to run on the top half of the fuel tank.
One of the most important tips for diagnosing a fuel delivery problem is to check the PCM for trouble codes indicating a faulty fuel level sensor or sending unit. Another tip is to compare the fuel gauge reading with the relative level observed in the fuel tank after the pump assembly has been removed. If the fuel gauge proves to be inaccurate, it’s entirely possible that the driver is running his vehicle too low on fuel.
 
Relays And Resistors

When replacing a fuel pump on a vehicle with more than 100,000 miles on the odometer, the reliability of the repair can usually be increased by replacing the fuel pump relay as well. A relay wears out because it’s an electrically operated switch with two tungsten contacts that connect the fuel pump to battery voltage. In many cases, the relay contacts oxidize and fail to close properly, which can create an intermittent cranking, no-start complaint. In other cases, the contacts can stick together, which allows the fuel pump to drain the battery with the ignition turned off.

------------fuel pumps continued-----------

Fuel Filters
During the 1990s, most manufacturers began integrating their fuel filters into a fuel pump module that also contained the fuel level gauge and fuel pressure regulator. Consequently, it’s easy to forget the many vehicles on the road that are still equipped with frame or engine-mounted fuel filters. The problem with replaceable fuel filters is that they can clog with sediment and cause many intermittent low-power engine performance complaints. Not only that, a partially clogged fuel filter can cause a premature fuel pump failure because the pump must work much harder to force fuel through a clogged fuel filter. So, when selling a non-modular fuel pump, avoid warranty returns and add to your bottom line by suggesting a fuel filter replacement.

 
Fuel Pressure Regulators
The fuel pressure regulator is usually mounted at the end of the fuel injector mounting rail on conventional dual-line fuel injection systems. As mentioned above, the fuel pressure regulator is contained internally on most single-line, modular fuel pump assemblies. The difference between dual and single line systems is that the dual-line system is made up of a high-pressure fuel supply line and a low-pressure fuel return line from the pressure regulator to the fuel tank. The single-line system returns pressure from the regulator directly to the fuel tank.
Fuel pressure regulators can affect fuel pump performance if they fail. In some rare cases, the internal pressure regulation spring can break, which will reduce fuel pressure. In most cases, the pressure regulator will stick closed or the return line will become restricted, which will cause the fuel pump to operate at maximum fuel pressure. High fuel pressure will cause the engine to run very rich on fuel and also might cause the new fuel pump to fail.

Before throwing out a suspected failing fuel pump, I would advice you check the amount of pressure the pump gives directly and through the pressure regulator, directly a fuel pump will provide over 70psi but dependent on the type of pressure regulator the pump should provide between 30-50psi, it is essential to know the amount of pressure required in your vehicle to rule out failure from the fuel pump or pressure regulator. Below are pictures of presure regulators and clogged filters.

All About Fuel Pumps

The fuel pump is an essential component of any vehicle with an internal combustion engine, principally, cars and trucks. With the job of forcing fuel from the gas tank towards the engine, a malfunctioning fuel pump will create a situation where the engine either gets too much or too little fuel due to too much or too little pressure in the line travelling from the tank to the engine. This will lead to performance issues with the car or truck itself.

In the most basic sense, in order for an engine to run properly, fuel in the form of liquid gasoline needs to travel from the tank where it is stored to the engine where it is burned to create power and propel the vehicle. Some smaller, more concisely constructed vehicles, such as certain models of motorcycles,, do not require a fuel pump because gravity takes care of this job. However, this is not the case for most internal combustion engined vehicles. Instead, they utilise either a mechanical or electronic fuel pump.

The Mechanical Fuel Pump

Traditionally, all fuel pumps were always mechanical. This means that they operate through a system that runs off of the rotation of the engine itself. A mechanical fuel pump resembles a diaphragm. It uses the pumping action of that diaphragm shape to create low pressure (10 to 15 psi) and transport fuel from the gas tank to the carburettor.. This action resembled that of a piston.

Mechanical fuel pumps are located on a mount outside of the fuel tank itself and, in general, are less likely to malfunction than electronic fuel pumps. The most common malfunction of mechanical fuel pumps comes when the diaphragm inside the pump splits, disturbing the pressure balance of the pump. The other cause for mechanical fuel pump malfunction is high heat created from both the engine and the air outside turning the fuel to vapour. This prevents the pump from operating since it is designed to handle liquid only.

The Electronic Fuel Pump
Though the mechanical fuel pumping system was always sufficient for carburetor-based fuel systems, eventually vehicle manufacturers moved past the use of carburettors in favour of a more advanced fuel injection system.. Though the fuel pump itself is still necessary, the mechanical pump can not generate the level of pressure needed to work with fuel injection engines. Therefore, a new system which delivers fuel under high pressure (40 to 60 psi) was created. This system is what is known as an electronic fuel pump.

Nowadays, most vehicles use an electronic fuel pump,, which is located within the gas tank itself, to deliver fuel to the engine. However, there are far more inherent issues with electronic fuel pumps. The electronic system works by spraying a fine mist of fuel inside the engine’s chambers and is operated through a computer control system rather than a mechanical one. As a result, both issues with the pump itself as well as the computer used to operate it can lead to vehicle and fuel pump malfunction.

After understanding the function of a fuel pump itself as well as the important differences between mechanical and electronic fuel pumps, understanding the common symptoms of problems with this component will make more sense. Remember, the purpose of a fuel pump is twofold:

It pushes (or pumps) fuel from the gas tank to the fuel injector or carburettor.
It creates the proper amount of pressure (low or high) to ensure that the right amount of fuel will be delivered to the engine, regardless of external conditions.
Therefore, malfunctions in the fuel pump can result from an issue in either one of these processes. Let’s take a look at the common signs of these problems.

1. The Engine Sputters at High Speed
The most common early sign of a problem with a fuel pump comes when driving a vehicle at a consistent high speed. While travelling down the road, the car will run well for about 10 miles and then begin to jerk around, or sputter, for a mile or two before returning to normal.

What This Means
Many people will mistakenly diagnose a sputtering vehicle as one with "dirty" gas or some other fuel-related issue. And while that can be the case, it is not uncommon for a fatigued fuel pump to create this same symptom as it struggles to supply a constant stream of fuel to the engine at the proper pressure. The loss of pressure causes the engine to sputter.

2. Vehicle Loses Power While Accelerating
The feelings generated by this second symptom are very similar to the first. However, rather than experience a sputtering sensation while driving, vehicles will experience it upon acceleration from a stop. Generally, the vehicle will initially move before making noises and jerking around as if it will stall. Then, it will continue on its acceleration path smoothly.

What This Means
The process of acceleration creates an increased demand for fuel by the engine. A malfunctioning fuel pump, again, cannot maintain the required pressure to deliver this fuel in a steady manner, thereby causing the engine to improperly mix fuel and air and lose power. Once pressure is restored, the engine is able to run smoothly and the car takes off.

3. Sudden Loss of Power When the Vehicle Is Under Stress
A car or truck is put under stress when the work needed to complete an ordinary task, such as forward movement, is somehow hindered by external forces. Generally, this occurs when climbing a hill or when hauling a load. If, when completing these tasks, the vehicle loses power, cannot accelerate, or begins to sputter, the fuel pump is a possible culprit.

What This Means
Generally, a fuel pump, even an ageing one, can maintain a steady stream of fuel and pressure when operating under normal conditions. However, once put under stress, the weakening elements of the pump will begin to take control and the fuel delivery will not be able to keep up with its demands, leading to power loss.

4. Surging
The opposite effect of the above symptoms, surging, can also be a sign of a malfunctioning fuel pump. A car that surges will be moving along normally at a consistent speed. Then, with no driver intervention, will pick up and "surge" forward, as if the gas pedal had been depressed.

What This Means
This is something that many people will mistakenly blame on the fuel filter since it is not "like" any of the other fuel pump malfunction signs. However, this surge is created because, as a result of age and normal wear and tear, the fuel pump now has irregular resistance within its motor. This creates a situation where the pump cannot draw enough electricity to maintain the pressure needed for steady speeds and may "surge" with a sudden ratcheting up in pressure.

5. The Engine Will Not Start
The final symptom of a malfunctioning fuel pump is also the most severe. Drivers who ignore the signs listed above will all eventually end up here. When a car or truck’s engine will not start as a result of a fuel pump malfunction. Basically, the engine will rev, but it will not catch.

What This Means
When a fuel pump has malfunctioned to the point that the car will no longer start, this means that there is no fuel reaching the engine upon ignition. For that reason, drivers will hear the sparks try to ignite, but there will be no fuel to burn. To diagnose a fuel pump malfunction, check for a blown fuse and pressure in the fuel line (it will be 0).

Conclusion
As an essential element of any internal combustion engine system, the fuel pump is one of those automotive issues all drivers need to keep in mind. Like any aspect of vehicle operation, understanding what a fuel pump does and the different ways that it can fail can help drivers avoid bad situations with a failing car or truck. With the important tasks of delivering fuel to the engine as well as maintaining a consistent stream of pressure while doing so, a malfunctioning fuel pump will present in several ways.

The 5 most common symptoms of a malfunctioning fuel pump include sputtering at high speeds, loss of power during acceleration, loss of power to the vehicle while under stress, surging, and, finally, an engine that will not start. Understanding these symptoms and correctly identifying them early is the only way that drivers can avoid getting to the point where their vehicle will not start, stranding them and costing a lot of money in repairs.

Engine coolant temprature sensor

The coolant temperature sensor is used to measure the temperature of the engine coolant of an internal combustion engine. The readings from this sensor are then fed back to the Engine control unit (ECU). This data from the sensor is then used to adjust the fuel injection and ignition timing. On some vehicles the sensor may be used to switch on the electronic cooling fan. The data may also be used to provide readings for a coolant temperature gauge on the dash. The coolant temperature sensor works using resistance. As temperature subjected to the sensor increases the internal resistance changes. Depending on the type of sensor the resistance will either increase or decrease.

Operation of the cooling Fan(s)


Like the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature in most cars like my peugeot 406 the fan starts up around 87-88 degrees Celsius and stays on until the temp drops to 79degress.

Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the engine points toward the side of the car. The fans are controlled either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.
Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This special viscous clutch is much like the viscous coupling sometimes found in all-wheel drive cars.

Connecting the fans to work all the time when the engine is running is bad for the engine and will reduce engine life and cause engine to burn more fuel.

Read about Thermostat https://www.nairaland.com/1788778/maintenance-tips-cars-quick-response

amosfunmi: House kindly help me out. My 1995 Mazda 626 stalled while driving and refused to start, though it cranked but could not just start.

Are you good at (Do it your self) if not most of our solutions will not make any sense

Carburettor or injector?

1. Run through the fuses.

2.Does the engine crank? If yes is it unnessearily fast? If yes check timing belt.

3 if not timing belt check ti you have a spark while cranking, instead of shocking your self (rd side mechanic style) just get a spark plug connect to one of the spark plug caps place the spark plug on ground(-) and crank you should see a spark if not.

4. Also check that you have petrol.

Answer first question then we can continue.

"Read power control module(PCM) and transmission control module c
odes"

Please edit.

Nice one good work.

Sms was 10naira this evening to other networks.

baconline: i mean a backup that i can synchronise back in the future. all my threads especailly

That's a long thing........ When you get it let me know I'm interested too

Very simple, copy and paste to note pad(if using a computer) rename for post title, if it has pictures use microsoft word. That's the easy way.

On a phone copy and paste to memo.

For others a fresh strart was a good thing. It reduced scamers by a whole lot. But a lot of info was lost, its really sad. But I didn't pay for the account so y I go de vex?

So a medical dr drove off with your car and you gave him all the original papers. This looks like an incomplete deal.

Did you say manual? Wow engine and interior pics please

This ia a rugged camry and it looks well maintained sweet wheels.

Gear oil leak. I what colour is the oil? I'm assuming its transmission oil u mean. Problem should be a worn out seal drive to a pit go under your car and visually inspect. Oils leaks could also be coming from power steering or engine.

Gear and soft jerk. Open bonnet(Get someone to help you with the testing) with parking brakes engaged properly and you standing by the side of the car "not in front" try to move the car gently, the movement of the engine should reveal broken engine mounts you have 4 mounts. Also try scanning in case there's a transmission fault.

Sluggish first gear. I don't understand the question.


High fuel consumption: scan car if you have an amber check light on instrument cluster(dash board) high fuel consumption could be caused by so many things a scan will narrow it down.

Shed more light on What ur transporting, and on what kind of terrain.

What about the opel brands? They share a lot of Parts with chevrolet, I've even seen engine swaps between such models.

Most of my posts were also hidden, I thought I was the only one.........

Ignition timing

This is the process of setting the angle relative to piston position and crankshaft angular velocity that a spark will occur in the combustion chamber near the end of the compression stroke.

The need for advancing the timing of the spark is because fuel does not completely burn the instant the spark fires, the combustion gasses take a period of time to expand, and the angular or rotational speed of the engine can lengthen or shorten the time frame in which the burning and expansion should occur. In a vast majority of cases, the angle will be described as a certain angle advanced before top dead center (BTDC). Advancing the spark BTDC means that the spark is energized prior to the point where the combustion chamber reaches its minimum size, since the purpose of the power stroke in the engine is to force the combustion chamber to expand. Sparks occurring after top dead center (ATDC) are usually counter-productive (producing wasted spark, back-fire, engine knock etc.) unless there is need for a supplemental or continuing spark prior to the exhaust stroke.

Setting the correct ignition timing is crucial in the performance of an engine. Sparks occurring too soon or too late in the engine cycle are often responsible for excessive vibrations and even engine damage. The ignition timing affects many variables including engine longevity, fuel economy, and engine power. Modern engines that are controlled in real time by an engine control unit use a computer to control the timing throughout the engine's RPM and load range. Older engines that use mechanical spark distributors rely on inertia (by using rotating weights and springs) and manifold vacuum in order to set the ignition timing throughout the engine's RPM and load range.

Early cars required the driver to adjust timing via controls according to driving conditions, but this is now automated.

There are many factors that influence proper ignition timing for a given engine. These include the timing of the intake valve(s) or fuel injector(s), the type of ignition system used, the type and condition of the spark plugs, the contents and impurities of the fuel, fuel temperature and pressure, engine speed and load, air and engine temperature, turbo boost pressure or intake air pressure, the components used in the ignition system, and the settings of the ignition system components. Usually, any major engine changes or upgrades will require a change to the ignition timing settings of the engine.

There's a trick I learnt a long time ago when my cooling fans failed as I was travelling, I just turned on my cars heater put it on full blast brought down the windows and faced the vents out the window, the trip was uncomfortable but temp stayed withing drivable limits. I also had to drop speed to 80km/hr

Thanks for the contribution ikenna

OXYGEN SENSORS.

Every new car, and most cars produced after 1980, have an oxygen sensor. The sensor is part of the emissions control system and feeds data to the­ engine management computer. The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.
A gasoline engine burns gasoline in the presence of oxygen. It turns out that there is a particular ratio of air and gasoline that is "perfect," and that ratio is 14.7:1 (different fuels have different perfect ratios -- the ratio depends on the amount of hydrogen and carbon found in a given amount of fuel). If there is less air than this perfect ratio, then there will be fuel left over after combustion. This is called a rich mixture. Rich mixtures are bad because the unburned fuel creates pollution. If there is more air than this perfect ratio, then there is excess oxygen. This is called a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some cases, it can cause poor performance and even engine damage.
Th­e oxygen sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The mechanism in most sensors involves a chemical reaction that generates a voltage . The engine's computer looks at the voltage to determine if the mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly.
The reason why the engine needs the oxygen sensor is because the amount of oxygen that the engine can pull in depends on all sorts of things, such as the altitude, the temperature of the air, the temperature of the engine, the barometric pressure, the load on the engine, etc.
When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs poorly and uses more fuel than it needs to.

How stuff works.

Thank you ogoplus.

Sorry I forgot to add MAP , or manifold absolute pressure sensor, on a 1989-96 Honda Accord is located in the engine compartment on the passenger side of the firewall. It is near the top and is easily accessible.

oride: Good news guys,
The problem has been fixed. A friend introduced me to his mechanic who fixed it in record time. The unfortunate thing is I stepped away for a bit and didn't see what he did and he refused to tell me what went wrong.
Anyways, I really appreciate your inputs. Cheers.

Tyres-------x
Wheels-----x
Bearings---yes probably not bollted well.

Raising your car is not a very good idea, you might end up damaging cv joints(shafts), and sacrificing vehicle stability. If you want to raise vehicle buy replacement suspension for same brand of car with higher clearance.

Back to your high fuel consumption. Your car has an ecu that regulates fuel injection presently your car is running rich which is leading to poor fuel mileage and possibly in limp mode, my suggestions to your problems are as follows

1. Check for fuel leaks while engine is running

2.Has your return pipe been blocked? If yes remove it. Most mechanics block the return pipe when the fuel pump is failing to increase the pressure getting to the injectors, this form of abuse will cause the injectors to leak or stay on for longer periods.

3. Water Temperature sensors. The ecu receives signals from the water temperature sensor to determine how long the injectors stay on when in operation. A failing or not connected sensor will cause high consumption

4.Oxygen sensor since your car is a 1991 model and oxygen sensors are to be changed every 100k miles ill suggest you just replace. (with a brand new oem one)

5.Faulty or leaking injector. This is a rear occurrence but its possible could be caused by blocking pressure regulation valve or bad ecu(brain box)

6. Retarded timing. Your timing marks might not match up, have them checked.

7. Bad spark plugs

8. Clogged air box (air filter) if your air filter is blocked of the filter head clogged car will consume more petrol

9.Bad wire harness, check your engine wiring to ensure the wires are not ripped and touching each other clean up your wiring if its not in order.

10. After all the aforementioned if car is still consuming petrol you might have a bad ecu/ecm (brain box) best way to eliminate is to find similar vehicle and test to see if you have same problem.

Best of luck.

How to Tell if Your Car's Thermostat Is Stuck Closed(will cause overheating) ...................Continued.....................


Step 1. Start your car and let it sit idling for a while. Or, take it for a sort drive to warm up the fluid in the radiator.

Step 2. Open the hood, with the engine still running. (You may want to put on a pair of gloves for this.) Find the top radiator hose (the one that connects to the thermostat housing).

Step 3. Put on an oven mitt or a heat-resistant glove. Near the middle of the hose, squeeze the hose, as if you were trying to squeeze it shut.

Step 4.Release it, and you should feel a surge as the water comes through. If it is too firm to squeeze the thermostat is stuck closed.

How to Tell if Your Car's Thermostat Is Stuck Closed(will cause overheating)

The thermostat in your car is responsible for controlling the amount of coolant released into your engine. When your car first heats up, the thermostat closes and does not allow coolant into the engine until it is warmed up. The thermostat should open and allow coolant in once the engine is adequately heated. Sometimes the thermostat fails and remains closed.

How to test a thermostat DIY

Step 1. Check your temperature gauge in the car. A stuck thermostat might be to blame if your gauge marker nears the red danger zone within 5 to 15 minutes.


Step 2. Allow engine to cool(never open the preasure cap of a radiator when its hot)


Step 3. Unfasten the radiator drain cock located near the bottom of the radiator and allow some of the coolant to drain out into a container with a lid until the level is below the upper radiator hose.


You might not need to drain the radiator, depending on the amount your reservoir holds. The amount drained is roughly 1 to 2 qt. (4 to 8 cups). You can reuse this coolant if it is brand new. Otherwise, replace it with new coolant.

Step 4. Locate your thermostat. The thermostat housing is usually under the upper radiator hose. Unbolt the housing and remove the thermostat, using a screwdriver and pliers. Take the thermostat inside.

Step 5. Fill a pan with water and place the thermostat into the water until it's completely submerged. Ensure that the part does not touch the bottom of the pan.

Step 6. Start heating the water and place a cooking thermometer into the water. Check the temperature frequently while monitoring the thermostat.


The thermostat should remain closed until about 190 ºF (88 ºC). At this temperature, you should see the thermostat begin to open.
The part should be completely open when the water reaches 195 ºF (90.6 ºC). If the thermostat is still closed at this point, it needs to replaced.

Making Sense of Engine Sensors


Computers can only do what they are programmed to do. If they get garbage in, they put garbage out. In an automotive engine control computer (called a Powertrain Control Module or PCM), the input data is not from a keyboard but electronic signals from various sensors. They act the like the engines eyes and ears helping it make the most of its driving conditions. Consequently, the Powertrain Control Module (PCM) can't do this if the inputs it receives are faulty or missing.

For example, the engine control system will not go into "closed loop," if the PCM does not receive a good signal from the coolant sensor or oxygen sensor. Nor can it balance the fuel mixture correctly if it does not receive good inputs from the throttle position sensor, MAP sensor or airflow sensor. The engine may not even start if the PCM does not get a signal from the crankshaft position sensor.

Sensors monitor all the key functions necessary to manage ignition timing, fuel delivery, emission controls, transmission shifting, cruise control, engine torque reduction (if the vehicle has antilock brakes with traction control) and charging output of the alternator. On many late model vehicles (Toyota, Nissan, etc.), the PCM even controls the throttle because there is no direct cable or linkage connection to the throttle. Reliable sensor inputs are an absolute must if the whole system is to operate smoothly.

.


COOLANT SENSOR


Usually located on the cylinder head or intake manifold, the coolant sensor is used to monitor the temperature of the engine coolant. Its resistance changes in proportion to coolant temperature. Input from the coolant sensor tells the computer when the engine is warm so the PCM can go into closed loop feedback fuel control and handle other emission functions (EGR, canister purge, etc.) that may be temperature dependent.

Coolant Sensor Strategies: The coolant sensor is a pretty reliable sensor, but if it fails it can prevent the engine control system from going into closed loop. This will result in a rich fuel mixture, excessive fuel consumption and elevated carbon monoxide (CO) emissions - which may cause the vehicle to fail an emissions test.

A bad sensor can be diagnosed by measuring its resistance and watching for a change as the engine warms up. No change, or an open or closed reading would indicate a bad sensor.

OXYGEN (O2) SENSOR


Used on both carbureted and fuel injected engines since 1981, the oxygen (O2) sensor is the key sensor in the fuel mixture feedback control loop.

Mounted in the exhaust manifold, the O2 sensor monitors the amount of unburned oxygen in the exhaust. On many V6 and V8 engines, there are two such sensors (one for each bank of cylinders).

The O2 sensor generates a voltage signal that is proportional to the amount of unburned oxygen in the exhaust. When the fuel mixture is rich, most of the oxygen is consumed during combustion so there is little unburned oxygen in the exhaust. The difference in oxygen levels between the exhaust inside the manifold and the air outside creates an electrical potential across the sensors platinum and zirconium tip. This causes the sensor to generate a voltage signal. The sensor's output is high (up to 0.9v) when the fuel mixture is rich (low oxygen), and low (down to 0.1v) when the mixture is lean (high oxygen).

Sensor output is monitored by the computer and is used to rebalance the fuel mixture for lowest emissions. When the sensor reads "lean" the PCM increases the on-time of the injectors to make the fuel mixture go rich. Conversely, when the sensor reads "rich" the PCM shortens the on-time of the injectors to make the fuel mixture go lean. This causes a rapid back-and-forth switching from rich to lean and back again as the engine is running. These even waves result in an "average" mixture that is almost perfectly balanced for clean combustion. The switching rate is slowest in older feedback carburetors, faster is throttle body injection systems and fastest in multiport sequential fuel injection.

If the O2 sensor's output is monitored on an oscilloscope, it will produce a zigzagging line that dances back and forth from rich to lean. Think of it as a kind of heart monitor for the engine's air/fuel mixture.

O2 Sensor Strategies: Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications should be replaced every 30,000 to 50,000 miles to assure reliable performance. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. On OBD II equipped vehicles, the recommended replacement interval is 100,000 miles. The O2 sensor's responsiveness and voltage output can diminish with age and exposure to certain contaminants in the exhaust such as lead, sulfur, silicone (coolant leaks) and phosphorus (oil burning). If the sensor becomes contaminated, it may not respond very quickly to changes in the air/fuel mixture causing a lag in the PCMs ability to control the air/fuel mixture.

The sensor's voltage output may decline giving a lower than normal reading. This may cause the PCM to react as if the fuel mixture were leaner than it really is resulting in an overly rich fuel mixture.

How common is this problem? One EPA study found that 70 percent of the vehicles that failed an I/M 240 emissions test needed a new O2 sensor.


MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR


The MAP sensor is mounted on or connected to the intake manifold to monitor intake vacuum. It changes voltage or frequency as manifold pressure changes. The computer uses this information to measure engine load so ignition timing can be advanced and retarded as needed. It performs essentially the same job as the vacuum advance diaphragm on an old fashioned mechanical distributor.

On engines with a "speed density" type of fuel injection, the MAP sensor also helps the PCM estimate airflow. Problems here may cause an intermittent check engine light (light comes on when accelerating or when the engine is under load), hesitation when accelerating, elevated emissions and poor engine performance. The engine will run with a bad MAP sensor, but it will run poorly. Some PCMs can substitute "estimated data" for a missing or out of range MAP signal, but engine performance will be drastically reduced.

MAP Sensor Strategies: Some MAP sensor problems are not the fault of the sensor itself. If the vacuum hose that connects the MAP sensor to the intake manifold is loose, leaking or plugged, the sensor cannot produce an accurate signal. Also, if there is a problem within the engine itself that causes intake vacuum to be lower than normal (such as a vacuum leak, EGR valve that is stuck open or leaky PCV hose), the MAP sensor's readings may be lower than normal.

THROTTLE POSITION SENSOR


Mounted on the throttle shaft of the carburetor or throttle body, the throttle position Sensor (TPS) changes resistance as the throttle opens and closes. The computer uses this information to monitor engine load, acceleration, deceleration and when the engine is at idle or wide open throttle. The sensor's signal is used by the PCM to enrich the fuel mixture during acceleration, and to retard and advance ignition timing.

Throttle Position Sensor Strategies: Many TPS sensors require an initial voltage adjustment when installed. This adjustment is critical for accurate operation. On some engines, a separate idle switch and/or wide open throttle (WOT) switch may also be used. Driveability symptoms due to a bad TPS can be similar to those caused by a bad MAP sensor: The engine will run without this input, but it will run poorly.

MASS AIRFLOW SENSOR (MAF)


Mounted ahead of the throttle body on multiport fuel injected engines, the MAF sensor monitors the volume of air entering the engine. The sensor uses either a hot wire or heated filament to measure both airflow and air density.

MAF Sensor Strategies: The sensing element in MAF sensors can be easily contaminated causing hard starting, rough idle, hesitation and stalling problems. Cleaning a dirty MAF sensor with electronics cleaner can often restore normal sensor operation and save the cost of having to replace the sensor (which is very expensive!).


VANE AIRFLOW SENSOR (VAF)


The VAF sensor has a mechanical flap-style sensor that is used on Bosch and other import multiport fuel injected engines. The function is the same as a mass airflow sensor, but air pushing against a spring-loaded flap moves a rheostat to generate an electronic signal.

VAF Sensor Strategies: The drivability symptoms for the VAF are the same as those of a mass airflow sensor if the sensor fails.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR


Mounted on the intake manifold, this sensor changes resistance to monitor incoming air temperature. The sensor's input is used to adjust the fuel mixture for changes in air density.

MAT Sensor Strategies: Problems with the manifold air temp sensor can affect the air/fuel mixture, causing the engine to run rich or lean.

CRANKSHAFT POSITION SENSOR


Used on engines with distributorless ignition systems, the crankshaft position (CKP) sensor serves essentially the same purpose as the ignition pickup and trigger wheel in an electronic distributor. It generates a signal that the PCM needs to determine the position of the crankshaft and the number one cylinder. This information is necessary to control ignition timing and the operation of the fuel injectors. The signal from the crank sensor also tells the PCM how fast the engine is running (engine rpm) so ignition timing can be advanced or retarded as needed. On some engines, a separate camshaft position sensor is also used to help the PCM determine the correct firing order. The engine will not run without this sensor's input.

There are two basic types of crankshaft position sensors: magnetic and Hall effect. The magnetic type uses a magnet to sense notches in the crankshaft or harmonic balancer. As the notch passes underneath, it causes a change in the magnetic field that produces an alternating current signal.

The frequency of the signal gives the PCM the information it needs to control timing. The Hall effect type of crank sensor uses notches or shutter blades on the crank, cam gear or balancer to disrupt a magnetic field in the Hall effect sensor window. This causes the sensor to switch on and off, producing a digital signal that the PCM reads to determine crank position and speed.

Crank Position Sensor Strategies: If a crank position sensor fails, the engine will die. The engine may, however, still crank but it will not start. Most problems can be traced to faults in the sensor wiring harness. A disruption of the sensor supply voltage (Hall effect types), ground or return circuits can cause a loss of the all-important timing signal.

KNOCK SENSOR


The knock sensor detects engine vibrations that indicate detonation is occurring so the computer can momentarily retard timing. Some engines have two knock sensors.

Knock Sensor Strategies: A failure with the knock sensor can cause spark knock and engine damaging detonation because the PCM will not know to retard ignition timing if knock is occurring.

BAROMETRIC PRESSURE (BARO) SENSOR


The baro sensor measures barometric pressure so the computer can compensate for changes in altitude and/or barometric pressure that would affect the fuel mixture or timing. Some MAP sensors also perform this function.

VEHICLE SPEED SENSOR (VSS)


The vehicle speed sensor, or VSS, monitors vehicle speed so the computer can regulate torque converter clutch lockup, shifting, etc. The sensor may be located on the transmission, differential, transaxle or speedometer head.

Vehicle Speed Sensor Strategies: A problem with the vehicle speed sensor can disable the cruise-control system as well as affect transmission shifting and converter engagement.

MAKING SENSE OF IT ALL

If you have not done your diagnostic homework and are replacing a sensor because you think it might be bad, you may be wasting money. Replacing a sensor won't solve a drivability or emissions problem if the problem is not the sensor. Common conditions such as fouled spark plugs, bad plug wires, a weak ignition coil, a leaky EGR valve, vacuum leaks, low compression, dirty injectors, low fuel pressure or even low charging voltage can all cause driveability symptoms that may be blamed on a bad sensor. If there are no sensor-specific fault codes, these kinds of possibilities should be ruled out before much time is spent on electronic diagnosis.

Copyright AA1Car