Is the Map Sensor Reading the Same as a Vacuum Gauge

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Manifold Accented Pressure MAP Sensors

past Larry Carley copyright 2019 AA1Car.com

The Manifold Absolute Pressure level (MAP) sensor is a key sensor because it senses engine load. The sensor generates a point that is proportional to the corporeality of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment.

When the engine is working difficult, intake vacuum drops as the throttle opens wide. The engine sucks in more air, which requires more fuel to keep the air/fuel ratio in balance. In fact, when the computer reads a heavy load bespeak from the MAP sensor, it usually makes the fuel mixture go slightly richer than normal and then the engine tin produce more power. At the same time, the computer will retard (back off) ignition timing slightly to prevent detonation (spark knock) that can damage the engine and hurt operation.

When conditions change and the vehicle is cruising along under low-cal load, coasting or decelerating, less ability is needed from the engine. The throttle is non open up very broad or may be airtight causing intake vacuum to increase. The MAP sensor senses this and the computer responds by leaning out the fuel mixture to reduce fuel consumption and advances ignition timing to clasp a petty more fuel economy out of the engine.

Typical MAP sensor outputs for an older GM application.

HOW A MAP SENSOR WORKS

MAP sensors are called manifold accented pressure sensors rather than intake vacuum sensors because they measure the pressure (or lack thereof) within the intake manifold. When the engine is not running, the force per unit area within the intake manifold is the same as the exterior barometric force per unit area. When the engine starts, vacuum is created inside the manifold past the pumping activity of the pistons and the brake created by the throttle plates. At full open throttle with the engine running, intake vacuum drops to almost zero and pressure level inside the intake manifold once again nearly equals the exterior barometric pressure.

Barometric pressure typically varies from 28 to 31 inches of Mercury (Hg) depending on your location and climate conditions. Higher elevations have lower air pressure than areas next to the ocean or someplace like Death Valley, California, which is actually beneath sea level. In pounds per foursquare inch, the atmosphere exerts fourteen.7 PSI at sea level on boilerplate.

The vacuum inside an engine's intake manifold, by comparing, tin can range from zero up to 22 inches Hg or more depending on operating conditions. Vacuum at idle is always high and typically ranges from 16 to xx inches Hg in well-nigh vehicles. The highest level of vacuum occurs when decelerating with the throttle closed. The pistons are trying to suck in air simply the closed throttle chokes off the air supply creating a high vacuum inside the intake manifold (typically 4 to five inches Hg higher than at idle). When the throttle is all of a sudden opened, as when accelerating hard, the engine sucks in a big gulp of air and vacuum plummets to zero. Vacuum so slowly climbs support as the throttle closes.

When the ignition cardinal is first turned on, the powertrain control module (PCM) looks at the MAP sensor reading before the engine starts to determine the atmospheric (barometric) force per unit area. And then in event, the MAP sensor tin serve double duty as a BARO sensor. The PCM then uses this information to adjust the air/fuel mixture to recoup for changes in air force per unit area due to tiptop and/or weather. Some vehicles use a separate "baro" sensor for this purpose, while others employ a combination sensor that measures both called a BMAP sensor.

On turbocharged and supercharged engines, the situation is a little more complicated considering under boost in that location may actually be positive force per unit area in the intake manifold. But the MAP sensor doesn't care because it just monitors the absolute pressure level within the intake manifold.

On engines with a "speed-density" electronic fuel injection system, airflow is estimated rather than measured directly with an airflow sensor. The calculator looks at the MAP sensor signal along with engine rpm, throttle position, coolant temperature and ambient air temperature to guess how much air is entering the engine. The computer may also take into account the oxygen sensor rich/lean signal and the position of the EGR valve, also, before making the required air/fuel mixture corrections to keep everything in balance. This approach to fuel management isn't as precise equally systems that use a vane or mass airflow sensor to measure actual airflow, but it is non as circuitous or as costly either.

Some other advantage of speed-density EFI systems is that they are less sensitive to vacuum leaks. Whatsoever air that leaks into an engine on the dorsum side an airflow sensor is "united nations-metered" air and actually messes up the fine balance that's needed to maintain an accurate air/fuel mixture. In a speed-density system, the MAP sensor will detect the slight drop in vacuum caused by the air leak and the figurer will recoup by adding more fuel.

On many GM engines that have a mass airflow sensor (MAF), a MAP sensor is besides used as a backup in example the airflow betoken is lost, and to monitor the performance of the EGR valve. No modify in the MAP sensor signal when the EGR valve is commanded to open would point a problem with the EGR system and set a fault lawmaking.

ANALOG MAP SENSORS

The MAP sensor consists of 2 chambers separated by a flexible diaphragm. I chamber is the "reference air" (which may exist sealed or vented to the outside air), and the other is the vacuum chamber which is continued to the intake manifold on the engine by a rubber hose or direct connection. The MAP sensor may exist mounted on the firewall, inner fender or intake manifold.

A pressure level sensitive electronic circuit inside the MAP sensor monitors the movement of the diaphragm and generates a voltage indicate that changes in proportion to force per unit area. This produces an analog voltage signal that typically ranges from 1 to 5 volts.

Analog MAP sensors accept a three-wire connector: basis, a five-volt reference signal from the estimator and the return signal. The output voltage normally increases when the throttle is opened and vacuum drops. A MAP sensor that reads i or two volts at idle may read 4.5 volts to 5 volts at wide open throttle. Output generally changes virtually 0.7 to 1.0 volts for every five inches Hg of change in vacuum.

FORD DIGITAL MAP SENSORS

Ford BP/MAP sensors (barometric pressure/manifold absolute force per unit area) likewise mensurate load merely produce a digital frequency signal rather than an analog voltage signal. This type of sensor has additional circuitry that creates a 5 volt "square moving ridge" (on-off) voltage indicate. The bespeak increases in frequency as vacuum drops.

At idle or when decelerating, vacuum is high and the BP/MAP sensor output may driblet to 100 Hz (Hertz, or cycles per 2nd) or less. At wide open up throttle when there is virtually no vacuum in the intake manifold, the sensor's output may jump to 150 Hz or higher. At zilch vacuum (atmospheric pressure), a Ford BP/MAP sensor should read 159 Hz.

MAP SENSOR DRIVABILITY SYMPTOMS

Anything that interferes with the MAP sensor's power to monitor the pressure differential may upset the fuel mixture and ignition timing. This includes a trouble with the MAP sensor itself, grounds or opens in the sensor wiring circuit, and/or vacuum leaks in the intake manifold (airflow sensor systems) or hose that connects the sensor to the engine.

Typical driveability symptoms that may be MAP related include:

* Surging.

* Crude idle.

* A rich fuel condition, which may crusade spark plug fouling.

* Detonation due to likewise much spark advance and a lean fuel ratio.

* Loss of power and/or fuel economy due to retarded timing and an excessively rich fuel ratio.

A vacuum leak will reduce intake vacuum and cause the MAP sensor to indicate a college than normal load on the engine. The computer will try to compensate by richening the fuel mixture and retarding timing -- which hurts fuel economy, performance and emissions.

MAP SENSOR CHECKS

Beginning, make sure engine manifold vacuum is within specifications at idle. If vacuum is unusually low due to a vacuum leak, retarded ignition timing, an exhaust brake (clogged converter), or an EGR leak (EGR valve not endmost at idle).

A depression intake vacuum reading or excessive backpressure in the exhaust system can trick the MAP sensor into indicating at that place is a load on the engine. This may result in a rich fuel condition.

A brake in the air intake (such as a plugged air filter), on the other hand, may produce higher than normal vacuum readings. This would result in a load depression indication from the MAP sensor and perchance a lean fuel condition.

A adept MAP sensor should read barometric air pressure when the key is turned on before the engine starts. This value tin can be read on a browse tool and should exist compared to the bodily barometric pressure reading to come across if they match. Your local weather channel or website should be able to tell you lot the current barometric pressure reading.

Bank check the sensor's vacuum hose for kinks or leaks. And so utilize a hand-held vacuum pump to check the sensor itself for leaks. The sensor should hold vacuum. Any leakage calls for replacement.

An outright failure of the MAP sensor, loss of the sensor signal due to a wiring trouble, or a sensor signal that is outside the normal voltage or frequency range will ordinarily set a diagnostic trouble code (DTC) and turn on the Check Engine low-cal.

MAP SENSOR SCAN TOOL CHECKS

On 1995 and newer vehicles with OBD Two self-diagnostics, a DTC lawmaking P0105 to P0109 would bespeak a fault in the MAP sensor excursion.

P0105....Manifold Accented Force per unit area/Barometric Pressure Circuit
P0106....Manifold Absolute Pressure/Baro Pressure out of range
P0107....Manifold Absolute Pressure/Baro Pressure Depression Input
P0108....Manifold Absolute Pressure/Baro Force per unit area High Input
P0109....Manifold Absolute Pressure/Baro Force per unit area Circuit Intermittent

On older pre-OBD II vehicles, the MAP codes are:

* General Motors: Codes 34, 33, 31

* Ford: Codes 22, 72

* Chrysler: Codes xiii, fourteen

On vehicles that provide data stream through a diagnostic connector and allow a scan tool to display sensor values, the MAP sensor'southward output voltage can be read and compared to specifications. Basically, y'all want to see a quick and dramatic change in the MAP sensor indicate when the throttle on an idling engine is snapped open up and shut. No modify would point a sensor or wiring mistake.

If the sensor is reading depression or at that place is no reading at all, bank check for proper reference voltage to the sensor. Information technology should exist very close to v volts. As well bank check the basis connection. If the reference voltage is low, check the wiring harness and connector for looseness, harm or corrosion.

Scan tools that display OBD II data will too display a "calculated load value" that can be used to determine if the MAP sensor is working or not. The load value is computed using inputs from the MAP sensor, TPS sensor, airflow sensor and engine speed. The value should be low at idle, and loftier when the engine is under load. No change in the value, or a higher than normal reading at idle might indicate a trouble with the MAP sensor, TPS sensor or airflow sensor.

If y'all display the MAP sensor output on a Digital Storage Oscilloscope (DSO), this is
what the waveform might look like as the throttle position, engine load and speed change.

MAP SENSOR BENCH TESTS

A MAP sensor can too be bench tested past applying vacuum to the vacuum port with a hand vacuum pump. With five volts to the reference wire, the output voltage of an analog MAP sensor should drib, and on a Ford digital MAP sensor the frequency should increase.

An analog MAP sensor's voltage tin can also be read directly using a voltmeter or oscilloscope. A digital MAP sensor's frequency signal can be read with a DVOM if information technology has a frequency function, or an oscilloscope. The leads would be connected to the signal wire and ground.

Warning : Practise Non use an ordinary voltmeter to check a Ford BP/MAP sensor because doing so can harm the electronics inside the sensor. This type of sensor can only exist diagnosed with a DVOM that displays frequency, or a scope or scan tool.

Another mode to check out a Ford digital MAP sensor excursion is to input a "simulated" MAP sensor signal with a tester that tin can generate an adjustable frequency signal. Changing the frequency of the simulated indicate should trick the computer into changing the fuel mixture (look for a change in the injector pulse width indicate).

No change would indicate a possible computer problem.

MAP SENSOR REPLACEMENT

If a MAP sensor needs to be replaced, make sure the replacement is the correct one for the awarding. Differences in scale between model years and engines volition bear upon the operation of the engine management arrangement.

If a vehicle is more than than five years old, the vacuum hose that connects the MAP sensor to the engine should likewise be replaced.

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Is the Map Sensor Reading the Same as a Vacuum Gauge

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