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desertjoe 
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Joined: 23 Sep 2013
Location: New mexico
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 Topic: what does a MAP sensor do,,,,?
Posted: 17 Apr 2022 at 7:43pm |
My little 2006 HHR has started to kinda jerk at stop signs like it wants to die,,,but running down the hiway it does just fine,,,no miss or nuttin,,,I run by Oreillys and they threw their tester on it and that was what their tester said was the problem.
I finally fount the dang MAP (Manifold Absolute Pressure) sensor down under the fuel rail and I guess it senses the manifold VACCUM then sends a signal of sorts to the ECU. As long as the engine is running,,,it SHOULD have some engine vaccum,,,right?? Wonder why they call it a Manifold Absolute "pressure" sensor,,,, The manifold always has a vaccum instead of pressure,,?The sensor plug has 3 pins I was thinking of sucking on the end while my meter is hooked to the pins to see if any change,,,?? Anyone got a clue,,,?
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Tbone95
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Joined: 31 Aug 2012
Location: Michigan
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Posted: 17 Apr 2022 at 8:19pm |
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Joe, they call it absolute pressure, because until there’s a perfect vacuum, there’s some pressure above 0 absolute. It’s like elevation versus sea level. Less air pressure but still some. So, absolute pressure measures vacuum, a number between 0 (perfect vacuum), and atmospheric (about 14.7 psi standard), indicating the level of vacuum.
Clear as mud? Feel like I didn’t say it very well.
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DiyDave
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Posted: 17 Apr 2022 at 8:36pm |
You should be able to test with a pump up vacuum tester, if the sensor has a vac hose going to it. You might have to rig up pipe fittings, to connect to the tester, if its a straight electrical unit... Consult youtube or a manual... 
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LouSWPA
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Posted: 17 Apr 2022 at 9:48pm |
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to add to what Dave said, I seriously doubt you can test it 'by mouth'. but, if nothing else, use a syringe, free from pharmacy, if you do not have a hand vac pump.
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I am still confident of this;
I will see the goodness of the Lord in the land of the living.
Wait for the Lord;
be strong and take heart and wait for the Lord. Ps 27
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LouSWPA
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Posted: 17 Apr 2022 at 9:51pm |
 Tbone95 wrote:
Joe, they call it absolute pressure, because until there’s a perfect vacuum, there’s some pressure above 0 absolute. It’s like elevation versus sea level. Less air pressure but still some. So, absolute pressure measures vacuum, a number between 0 (perfect vacuum), and atmospheric (about 14.7 psi standard), indicating the level of vacuum.
or 0 to 30" of mercury, round no's.
Clear as mud? Feel like I didn’t say it very well. |
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I am still confident of this;
I will see the goodness of the Lord in the land of the living.
Wait for the Lord;
be strong and take heart and wait for the Lord. Ps 27
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DaveKamp
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Posted: 17 Apr 2022 at 10:07pm |
Actually, most Manifold Absolute Pressure sensors' peizoelectric elements will measure ANY pressure, it's simply that MOST of the time, the absolute pressure in the manifold is substantially LOWER than ambient pressure.
Remember- ambient pressure is 'not' constant. A barometer reading now, and in 12 hours, will be different, because atmospheric pressure changes as a result of weather... and atmospheric pressure in Mecca, California, is not the same as that of Miami, Minneapolis, or Fort Bridger, Colorado.
Joe, the MAP sensor's job, is to identify to the EFI computer what amount of fuel will be necessary to provide a proper fuel mixture for the engine, under varying atmospheric conditions, and changes in THROTTLE POSITION.
The MAP sensor's primary partner is the Throttle Position Sensor (TPS), and it compares those to engine speed (the crankshaft position sensor and camshaft phase sensor), measures engine temperature through the Coolant Temp Sensor, and uses the front Exhaust Oxygen Sensor to make fine adjustments.
A carbeurator does exactly the same thing, in a mechanical, analog (non-digital) way... it compares atmospheric pressure (on the fuel in the float bowl) against pressure in the carb venturi (which is a demand signal created by airflow velocity change through the convergent and divergant zones) and meters out fuel based on that difference in pressure, AND... the surface area of the exposed fuel inside the fuel jet.
Can you test it? Yes, but no. You can see it respond on a test set, but you can't see what it looks like to the COMPUTER... a bad MAP can look perfectly fine, when it is, in fact, going berzerk. Same goes for the Throttle Position Sensor. It'll look just dandy on a voltmeter, but when the computer is trying to read it, a little worn-spot in that sensor will cause the computer to get some bad data, and it'll be all angry-stumbly.
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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steve(ill)
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Posted: 17 Apr 2022 at 10:42pm |
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MAP sensors do go bad...... I have a 2013 F150 with a turbo charged engine and the "MAP" actually measures BOOST pressure according to FORD... If the "expected pressure" goes "out of range" then the light comes on..... If it is on ALWAYS, then probably sensor is bad.. Mine would come on once a month and i had to reset.. Apparently the sensor was about 90% " correct" in measuring pressure... NEW SENSOR.. no little light for the past year.
Edited by steve(ill) - 17 Apr 2022 at 10:44pm
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fixer1958
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Posted: 18 Apr 2022 at 8:19am |
Well what I would do is put a vacuum gauge on it and see what the actual engine vacuum is reading idling. Should be steady around 16-18 inches. Just because it is flagging the map sensor doesn't mean that is the problem. Possibly a vacuum leak, rotted hose etc. Check the purge valve in the evap system. It's on the intake, one hose is dedicated manifold vacuum the other goes to the rear evap cannister area. If the solenoid sticks open it creates issues. More common stuff. Does it have oil in it? Those engines tend use oil and slowly eat themselves causing timing chain issues. Take a spark plug out and see what it looks like. Black? Sounds like it is possibly loading up to me. Look at the basic chit first before throwing parts on.
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dee_veloper
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Posted: 18 Apr 2022 at 12:53pm |
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