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By Counterman
In the automotive context, a solenoid converts electrical energy into mechanical work. It’s important to clarify this because from a scientific standpoint, a solenoid is defined as a type of electromagnet, with multiple different uses that ultimately aren’t relevant in the automotive space – nor would I be qualified to attempt an explanation that requires a deep understanding of physics.
But I can explain how an automotive solenoid works. Operation is based on electromagnetism, a concept that automotive technicians are very familiar with and learn early on with basic electrical theory.
Any time current passes through a conductor – in this case a wire – an electromagnetic field is generated. When the wire is wrapped tightly into multiple coils, the magnetic field is intensified. Since like poles repel each other magnetically, motion can be created by positioning a magnetic object in the generated field. This electrical fundamental is the basis of operation for solenoids, as well as electrical motors and alternators.
In the case of an electromechanical solenoid – the type we’re used to in the automotive context – the magnetic field acts upon a moveable armature, causing it to be pulled in a particular direction. The armature is connected either directly, or through a lever to another device, providing the mechanical movement to that device.
The advantage to solenoid operation is the speed with which a mechanical reaction can occur. One of the most common solenoids we’re used to is a starter solenoid. A look at the exploded view of a typical starter and solenoid (Figure 1) will help illustrate how a starter solenoid works.
Starter Solenoids
The starter solenoid has two functions, both of which use mechanical motion. When the windings in the solenoid are energized via the ignition switch circuit, the resulting magnetic force pulls the plunger into the solenoid. This causes the fork to throw the starter pinion outward to engage in the teeth on the engine flywheel. As the plunger reaches the end of its travel, it pushes together two large high-amperage contacts that allow the current from the battery to flow into the starter motor, causing it to rotate.
The starter solenoid is well-known by vehicle owners – even if they don’t know much else about cars – primarily due to their infamous reputation of causing a no-start problem. Also well-known is the “home” remedy to hit the solenoid or starter with a hammer to make it work. While this usually works for the first few times a problem occurs, it can easily damage the internal components of the solenoid or starter, and it’s not a recommended practice for this reason.
The common no-start symptoms related to a starter or its solenoid are:
No noise at all when attempting to start the vehicle A clicking noise A deeper clunk sound The sound of the starter motor spinning but not the engine When there’s no noise at all, the first thing to check is the starting circuit to make sure power is getting to the solenoid activation terminal.
A clicking noise can mean the solenoid is being energized, but unable to properly engage due to internal binding. However, this also is usually caused by a “dead” battery. A deep clunk sound indicates that the plunger is working properly and engaging the starter pinion into the flywheel, but current is not flowing into the starter, due to either a poor connection leading up to or within the solenoid or worn starter brushes.
If the starter motor alone spins, it means a problem with the mechanical action of the solenoid plunger, fork or starter pinion has prevented it from engaging the flywheel. The vibration from striking the starter can create a temporary solution to any of these problems, but temporary is the reality.
Other Solenoids
On today’s vehicles, there are many different types of solenoids. A push-and-pull solenoid is one that operates with a fixed range of travel, such as the starter solenoid described above. The plunger of the solenoid travels in one direction or the other (it may push, or it may pull) when energized, and a spring returns it to the non-energized position.
Another example of a push-and-pull solenoid is a trunk-release solenoid. Even though these are built into latch assemblies on most newer vehicles – and not so audibly intrusive – on older cars that featured trunk-release buttons on the dash you could hear the tell-tale clunk of the solenoid operating by pressing and releasing the button.
Power door locks utilize a solenoid that is considered a holding solenoid. By reversing the polarity, this type of solenoid will move in either direction, then remain in that position while unenergized until reverse polarity is applied.
Proportional Solenoids
Now it gets interesting. A proportional solenoid is one whose position can be controlled in a precise manner. The primary use for a proportional solenoid is to manage operation of pistons and valves for accurate control of fluid flow and pressure. For example, proportional solenoids are used in automatic-transmission valve bodies and for torque-converter lock-up control, fuel injectors, variable-valve-timing actuators and in antilock brake systems.
When compared to the basic electrical function of a push-pull or holding solenoid, proportional solenoids require a more advanced control. This control is pulse-width modulation (PWM), which is a method for controlling the amount of power sent to any given component. During PWM, the vehicle ECU continuously switches the power on and off in a circuit. The longer the power is on, the more power is sent to the circuit.
Determining the position of a PWM-controlled solenoid is achieved by the control unit monitoring the current flow through the solenoid. Along with all other forms of automotive technology, solenoids have evolved from basic electrical devices and control to highly precise actuators, relying on equally precise control to meet today’s demands of efficiency and performance. But they’re both still in use today.
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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 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 RockAuto
See what's new at RockAuto in the August Newsletter!
Headlines at RockAuto: Calorstat Cooling System Parts New RockAuto Commercial VW Golf Trivia "The Obvious Problem" Blunder CV Axle Lock Rings Denny's 1969 Pontiac Firebird And More...
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