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Camshaft and Crankshaft Sensors
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By Counterman
While it might not sound like it to the untrained ear, the orchestration of components to achieve the ideal combustion cycle is nothing short of a symphony.
For fuel-injected engines, two important instruments in this precise arrangement are the mass airflow (MAF) sensor and the manifold absolute-pressure (MAP) sensor.
The MAF sensor, typically situated between the air-filter housing and the intake manifold, might be considered the maestro. Also known as an air meter, the MAF sensor uses a heated element to measure the amount of air by weight that’s entering the engine. As the air cools the heated element, this cooling effect changes the electrical resistance of the element. The amount of cooling the element experiences is directly proportional to airflow, and the sensor conveys this information to the engine computer by way of changing voltages or digital frequencies.
The engine computer then uses this information – along with other inputs – to adjust the amount of air entering the engine.
Other inputs that help determine the proper air-fuel ratio include: oxygen sensors, which measure the amount of air in the exhaust gases; throttle-position sensors, which tell the computer if the throttle is closed, partially open or wide open; knock sensors, which monitor for signs of engine knocking; and (on some vehicles) MAP sensors, which measure the amount of pressure or vacuum in the intake manifold.
While most fuel-injected engines today utilize a MAF sensor to obtain a precise measurement of airflow, MAP sensors play a starring role in fuel-injected vehicles with speed-density engine-management systems. However, turbocharged engines often have both a MAF and a MAP sensor.
“In turbocharged engines, the partnership between MAP and MAF sensors isn’t just a technicality – it’s the secret behind the vehicle’s ability to harness forced induction with unparalleled precision,” Walker Products explains.
Let’s take a closer look at each type of sensor and what they bring to the table.
MAF Sensors
Air changes its density based on temperature and pressure. In automotive applications, air density varies with the ambient temperature, humidity, altitude and the use of forced induction (turbochargers and superchargers). Compensating for changes in air density due to these factors is essential for maintaining the optimal air-fuel mixture and efficient engine operation.
Consequently, MAF sensors are better-suited than volumetric-flow sensors to provide an accurate measurement of what the engine needs. MAF sensors offer a more direct and accurate measurement of the critical parameter for engine combustion: the mass of air. This facilitates better engine performance, fuel efficiency and emissions control compared to relying solely on volumetric-flow measurements.
There are two types of MAF sensors used in automotive engines: the vane-meter sensor and the hot-wire sensor.
The vane-type MAF was the first one out there, and it was used on import vehicles from the 1970s and 1980s.
“It didn’t have many actual problems,” Charles Dumont explains
link hidden, please login to view. “However, many of them were replaced, because back then the vehicles didn’t have onboard diagnostic capabilities. Usually after mechanics and DIYers had replaced all the other ignition parts and sensors, the MAF sensor was the last-ditch effort.” These days, you’re more likely to encounter the hot-wire style of MAF sensor. The hot-wire MAF sensor is smaller, faster and more accurate than the older vane-type MAF sensor, making it the preferred choice in most late-model vehicles.
Delphi provides a great explanation of the hot-wire MAF sensor
link hidden, please login to view. “Put simply, a MAF has two sensing wires,” Delphi explains. “One is heated by an electrical current, the other is not. As air flows across the heated wire, it cools down. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate. The current is then changed to a frequency or a voltage that is sent to the ECU and interpreted as air flow. The quantity of air entering the engine is adjusted accordingly.”
MAF sensors are pretty dependable, but there are a few things that can undermine their performance.
Any air or vacuum leaks downstream of the sensor can allow “unmetered” air to enter the engine. This includes loose fittings or clamps in the plumbing between the air-filter housing and throttle, as well as any vacuum leaks at the throttle body, intake manifold or vacuum-hose connections to the engine.
Anything that contaminates the surface of the sensor also can hinder its ability to respond quickly and accurately to changes in airflow. This includes fuel varnish and dirt deposits as well as any debris that might get past or flake off the air filter itself.
A frequent cause of MAF-sensor failure is directly related to the air filter. Low-quality or incorrectly installed air filters can allow paper particles or dirt to accumulate on the hot wire, effectively insulating it and affecting the reading of the sensor.
Oil-soaked air filters also can have an effect on MAF-sensor operation, so it’s important to warn someone of this possibility if they’re installing a performance high-flow filter. In some cases, modified intake systems can cause increased air turbulence, which can affect the performance of the MAF sensor as well.
A dirty MAF sensor can cause performance problems and, in some cases, trigger a diagnostic trouble code. You can recommend MAF-specific cleaners (any harsher solvents can ruin the sensor) and air filters as maintenance items before your customer spends the money on a replacement sensor.
Symptoms of a failing MAF sensor could include rough idling or stalling; RPM fluctuations without driver input; and a decline in fuel economy and engine performance. A problem with the MAF sensor often triggers a “Check Engine” light.
MAP Sensors
As the name implies, the primary function of a manifold absolute-pressure sensor is to measure the pressure within the intake manifold of an engine (usually a fuel-injected engine). Essentially, a MAP sensor is measuring the barometric pressure – the atmospheric pressure that’s pressing down on earth. Barometric pressure is influenced by changes in elevation, air density and temperature.
The pressure reading from a MAP sensor is an indicator of engine load, and it helps the engine computer calculate fuel injection for the optimal air-fuel mixture. The MAP sensor helps the engine adapt to different operating conditions, such as changes in altitude or driving up a steep incline, where air pressure can vary significantly.
A MAP sensor contains a sealed chamber that uses a flexible silicon chip to divide the sensor vacuum from the intake-manifold vacuum. As soon as the driver starts the vehicle, the MAP sensor is called into action, performing “double duty as a barometric-pressure sensor,” according to Delphi. With the key turned on but prior to the engine starting, there’s no vacuum in the engine applied to the MAP sensor, so its signal to the engine computer “becomes a baro reading helpful in determining air density.”
“When you start the engine, pressure in the intake manifold decreases, creating a vacuum that is applied to the MAP sensor,” Delphi explains on its website. “When you press on the gas accelerator pedal, the pressure in the intake manifold increases, resulting in less vacuum. The differences in pressure will flex the chip upward into the sealed chamber, causing a resistance change to the voltage, which in turn tells the ECU to inject more fuel into the engine. When the accelerator pedal is released, the pressure in the intake manifold decreases, flexing the clip back to its idle state.”
Typically, you’ll find the MAP sensor in the air cleaner, fender wall, firewall, intake manifold or under the dash, Standard Motor Products (SMP)
link hidden, please login to view. Given their location, MAP sensors commonly fail “due to the constant contact of the movable wiper arm over the sensor element and the exposure to the high underhood heat,” according to SMP. The high heat can melt or crack the electrical connectors. MAP sensors also are susceptible to contamination.
“If the MAP sensor uses a hose, the hose can become clogged or leak and unable to read pressure changes,” Delphi explains. “In some cases, extreme vibrations from driving can loosen its connections and cause external damage.”
A failing MAP sensor will compromise the engine’s ability to maintain the proper air-fuel ratio, leading to a number of potential symptoms. These symptoms could include noticeably poor fuel economy, sluggish acceleration and an odor of gasoline (signs of a rich air-fuel ratio); surging, stalling, hesitating, overheating and a general reduction in engine power (signs of a lean air-fuel ratio); higher emissions that can lead to a failed emissions test; erratic or unusually high idle; and hard starting or even a no-start condition. A faulty MAP sensor also can set off a “Check Engine” light.
Parting Thoughts
MAF and MAP sensors are small components that play a big role in modern fuel-injected engines. With turbocharged engines becoming more and more prevalent in some of the most popular models on the road today, these sensors should continue to play an important role in automakers’ fuel-economy and emissions-control strategies.
“As turbocharged technology evolves, understanding and optimizing the cooperative function of these sensors becomes the key to unlocking the full potential of modern turbocharged engines,” Walker Products explains.
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By Dorman Products
Rear Crankshaft Oil Seal Installer - 635-000 #automobile #technician #gm #carrepair
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By Counterman
Wheel-speed sensors aren’t new to any of us. They’ve been around for years, and their initial purpose was to provide wheel-speed data to the control unit for the antilock braking system (ABS). Because of this, they’re often called ABS sensors.
On today’s vehicles, however, the ABS isn’t the only system that utilizes wheel-speed data. Multiple safety and comfort systems such as advanced driver-assistance systems (ADAS), traction control and parallel-parking assist rely on wheel-speed data to function properly.
At a glance, all wheel-speed sensors may appear to be the same. But there are two different types: passive and active. Essentially, both have the same job of providing wheel-speed data to various control units, but they differ in how they do it and how well they do it.
Passive Wheel-Speed Sensors
Passive wheel-speed sensors are constructed with a permanent magnet and fine copper wire and generate a magnetic field. They operate in conjunction with a toothed metal ring, called a tone ring, which rotates at wheel speed. As the teeth of the tone ring pass through the magnetic field, it causes the polarity of the sensor to change and generates an alternating-current (AC) signal.
This AC signal is sent to the ABS control unit, which in turn must interpret it to determine when ABS operation is required. While passive sensors have been effective for many years, they have several drawbacks. A common problem with these and any type of permanent magnet sensor is limited operation at low speeds. In the case of wheel speed, a passive sensor is only able to generate a signal at approximately four miles per hour and higher.
They also do not generate a signal in reverse, and the gap between the sensor and the teeth on the tone ring is critical. Even the slightest amount of rust buildup underneath one of these sensors can cause erratic operation and unwanted activation of the ABS under braking. In addition, the magnetic field of these sensors can attract fine metal particles over time, which further inhibit proper system operation.
Active Wheel-Speed Sensors
The AC signal generated by a passive wheel-speed sensor is an analog wave, or a continuous smooth waveform. An active wheel-speed sensor, on the other hand, produces a digital signal, which is viewed as a square waveform. A digital signal is a very accurate and precise on/off signal.
Many of the other control units associated with today’s advanced systems rely on this type of precision for proper system operation. In addition to the accuracy, an active wheel-speed sensor can read wheel speed practically to zero mph, which is critical data for modern traction-control and driver-assistance systems, and some also can detect reverse wheel rotation.
Active wheel-speed sensors require power to operate, whereas passive units do not. There are two types of active wheel-speed sensors: a Hall-effect sensor and a magneto-resistive sensor. A Hall-effect sensor requires either a toothed or magnetic ring to generate a voltage signal, whereas a magneto-resistive sensor utilizes a slightly different type of encoder ring, allowing it to determine direction of wheel rotation.
The most important part about these sensors is knowing that they’re different. Visually they look the same, but functionally they’re not interchangeable. Some makes and models that are traditionally thought of as the “same” vehicle with different badging can utilize different sensors, even for the same model year.
When it’s all said and done, active wheel-speed sensors are necessary for today’s advanced systems, but regardless, all wheel-speed sensors take a lot of abuse, simply due to their location. Any time there’s a problem indicating a bad wheel-speed sensor, all components must be taken into account including the sensor itself, as well as the wheel bearing and CV joint, which may house or support the tone ring or encoder wheel necessary for sensor operation.
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By Counterman
Continental has added eight new part numbers to its line of OEM knock sensors.
The sensors are the same part that the vehicle manufacturer uses and deliver the exact fit, form and function as the original part, ensuring an easy installation and long service life, according to Continental.
The eight new part numbers provide application coverage for some of the most popular domestic, European and Asian makes and models on the road today. The expanded line covers Chrysler, Dodge, Ford, Infiniti, Jeep, Lincoln, Mercedes-Benz, Mercury, Nissan and Ram models ranging from 2000 to 2023. The new sensors provide coverage for 28.8 million vehicles in operation (VIO) in the United States and 2.4 million vehicles in Canada.
“Our newly expanded line was developed to meet the growing need for reliable knock sensors on some of the most common vehicles on the road today,” noted Brendan Bachant, Continental product manager for engine management and fuel. “The original sensors can be prone to failure due to mechanical damage, excessive vibration, high engine temperatures, and corrosion. Continental has made these OEM sensors available to the aftermarket so that professional technicians can easily and confidently service the most common vehicles in the shop, like the Ford F-150 and Explorer, the Jeep Wrangler and the Nissan Maxima and Altima. Technicians can be confident when choosing the Continental knock sensor that they will avoid comebacks.”
Knock sensors are designed to detect engine ping caused by pre-ignition and relay the information to the electronic control unit to adjust engine timing and help keep the engine running smoothly. These sensors are an ideal repair for a rough-running engine with a timing and knock-sensor fault code and will help shops to restore the performance of their customers’ vehicles to OE specifications, according to Continental.
Continental knock sensors are built in ISO-certified facilities to deliver the highest level of dependability, the company noted.
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By Counterman
As modern cars and light trucks continue to grow in complexity, their maintenance needs are changing. Component failures that were commonplace just a decade or two ago are becoming much less common today.
An example of this is the throttle-position sensor (TPS). This small plastic sensor would be mounted on the throttle body, usually on the opposite of the throttle cable. The TPS was used to tell the engine control unit (ECU) what angle the throttle body was being opened to by the driver, and the ECU would adjust the fuel as needed based on this data as well as other inputs.
A faulty TPS reading can cause a number of drivability concerns, including:
• Unexplained bucking or jerking of the engine
• Surging engine idle
• Engine stalling, stumbling or hesitation
These sensors were rather inexpensive and usually pretty easy to replace. They didn’t fail too often, but I can remember having to replace them on a few of my own vehicles, as well as some customer vehicles. So what happened to throttle-position sensors, and why don’t we see them as often today?
Throttle-By-Wire
Throttle-by-wire technology has been called by many names, but it operates on a simple principle – an electronic throttle body is used to meter the air entering the engine. This electronic throttle body is controlled by the ECU based on a number of inputs including accelerator-pedal position, mass airflow, manifold air pressure, wheel speed and more. But the important thing to understand is that there is no longer a mechanical link between the accelerator pedal under the dashboard and the throttle body on the engine. So why is this important?
By decoupling the accelerator pedal from the throttle body, automakers are able to precisely control the throttle angle in all operating conditions to maximize throttle response and traction, reduce emissions and improve fuel economy. Throttle-by-wire systems are able to maximize the benefits of variable-valve timing and direct fuel injection by precisely controlling how much air is introduced to the engine.
With the advent of throttle-by-wire systems, we’ve seen a change in how the ECU measures the throttle position. The TPS still is being used today, but it’s now incorporated into the electronic throttle body. In fact, some electronic throttle bodies may contain more than one TPS. By using multiple sensors, the ECU can monitor and compare both sensor inputs. Redundancy in electronic systems can be a very good thing.
We’ll talk more about the pros and cons of throttle-by-wire a little bit later, but the fact that the TPS is now incorporated into the electronic throttle body can be a big drawback down the road. You see, it means that the system is now less serviceable than it was in the past. If a TPS failed on a cable-driven throttle body, you could replace the sensor for around $30 to $40 and be back on the road. If a TPS fails inside an electronic throttle body, now you have to replace the entire unit, and that could cost hundreds of dollars.
Then, after the electronic throttle body has been replaced, you’ll need to perform a “relearn procedure” so the ECU can learn how the new throttle body reacts to input, and where the internal mechanical stops are located. Failing to perform this critical step can cause a number of drivability concerns, and a costly customer comeback.
There has been a trend in the automotive space for quite some time now where components are becoming more and more “modular.” When I say “modular,” I really mean “pre-assembled.” After all, vehicles are engineered to go down the assembly line as fast as possible. They’re not engineered to be easy to work on. So it makes sense that automakers would get creative with incorporating certain components together into a modular assembly that can be installed more quickly. Of course, the major drawback with this idea is that the replacement costs are increased, and that cost will eventually fall onto the vehicle owner once the warranty period expires.
Advantages & Disadvantages of Throttle-By-Wire
Throttle-by-wire systems offer a number of advantages. They contain fewer moving parts, so that means less maintenance and lower overall vehicle weight. Their precision allows for improved fuel economy and reduced tailpipe emissions, as well as a better overall driving experience for the typical driver. Finally, the throttle body can be used to help the traction or stability control regain vehicle control.
These systems also have a few drawbacks. They’re more expensive to develop, manufacture and replace. They’re more complex due to the wiring and electronic control units that are used. Some drivers may complain about a time delay or “lag” in engine response after they change their accelerator-pedal input.
Finally, they’re harder to service for technicians. Sure, there aren’t any cables or linkage points to grease or maintain, but the real difficulty lies in the electronic controls. Complex wiring and communication systems are needed in order to control the electronic throttle body and related systems. There also are special procedures that must be followed whenever servicing the electronic throttle body. If an electronic throttle body is replaced, the relearn procedure must be performed. This has a profound effect on engine performance, drivability and idle quality.
If you find yourself selling a replacement electronic throttle body to a customer, there are a few questions you should be asking. Do they have a scan tool that’s capable of bi-directional control? A simple code reader won’t work here. They need the real thing in order to relearn the new electronic throttle body. Many electronic throttle bodies are installed in plastic intake manifolds, so it’s a good idea to sell them a new throttle-body seal as well. Finally, it’s a good idea to check with the customer to see if they’ve inspected the wiring harness and connections for any signs of rubbing, fraying or other issues. These sorts of problems can come back to bite them later on down the road.
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