MAP sensor
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Senior User
Joined: Jun 2004
Posts: 164
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From: yuba city, ca
MAP sensor
Hows it going everyone? I have narrowed a problem down to the map sensor. I would just like to know the purpose of this do-hickey as I am new to working on fuel injection cars. 90 aerostar 3.0 by the way.
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
Muffinman I hope it's ok if I argue with you 
MAP stands for Manifold Absolute Pressure. MAF is Mass Air Flow.
A MAP sensor basically senses the manifold vacuum in the engine to tell the PCM how much load is on the engine. The air flow etc is inferred from the vacuum reading and TP reading etc.
A bad MAP wont always show up in tests and can cause rough idle, stalling, black smoke etc. They dont go bad too often though.
MAP stands for Manifold Absolute Pressure. MAF is Mass Air Flow.
A MAP sensor basically senses the manifold vacuum in the engine to tell the PCM how much load is on the engine. The air flow etc is inferred from the vacuum reading and TP reading etc.
A bad MAP wont always show up in tests and can cause rough idle, stalling, black smoke etc. They dont go bad too often though.
Posting Guru
Joined: Jun 1999
Posts: 1,642
Likes: 6
From: Northern California
Racerguy is 100% correct! MAP sensors are another one of those parts, that the aftermarket produces a lot of junk crap. You can replace the Motorcraft factory part, for one that is much cheaper in price. 6-7 months later the problem returns, usually when you least need it (the week of Christmas with rain or snow!!) I learned the hard way. For example, I replaced my Map sensor at around 95,000 miles when the emissions and driveability issues went wacko. Balked at the dealer price. Used a Carquest part, lasted 5 months same symptoms. Replaced with Auto zone part, another 6-7 months then crappy performance returns. I know instantly what the problem is when it happens, usually with little or no warning. That is about a 3,000 mile timeframe between the two aftermarket sensors. Bite the bullet, and purchase a Motorcraft MAP sensor. Almost 40,ooo miles on the Motorcraft MAP sensor, and the van runs fine in all types of driving conditions. True story... ED
Laughing Gas
Joined: Jun 2004
Posts: 1,240
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From: Dallas, Texas
Originally Posted by Racerguy
Muffinman I hope it's ok if I argue with you
MAP stands for Manifold Absolute Pressure. MAF is Mass Air Flow.
MAP stands for Manifold Absolute Pressure. MAF is Mass Air Flow.
Thread Starter
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Senior User
Joined: Jun 2004
Posts: 164
Likes: 0
From: yuba city, ca
Originally Posted by Racerguy
Muffinman I hope it's ok if I argue with you
MAP stands for Manifold Absolute Pressure. MAF is Mass Air Flow.
A MAP sensor basically senses the manifold vacuum in the engine to tell the PCM how much load is on the engine. The air flow etc is inferred from the vacuum reading and TP reading etc.
A bad MAP wont always show up in tests and can cause rough idle, stalling, black smoke etc. They dont go bad too often though.
MAP stands for Manifold Absolute Pressure. MAF is Mass Air Flow.
A MAP sensor basically senses the manifold vacuum in the engine to tell the PCM how much load is on the engine. The air flow etc is inferred from the vacuum reading and TP reading etc.
A bad MAP wont always show up in tests and can cause rough idle, stalling, black smoke etc. They dont go bad too often though.
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Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
Yes, a vacuum leak or bad fuel pressure regulator, possible bad O2 sensor can all cause it. If you know someone with a Ford with a MAP sensor that you could try that would be a quick and easy test.
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Joined: Apr 2001
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Likely the fuel pressure regulator then. The regulator is a round, shiny, chrome plated affair on the fuel rail atop the upper manifold. It has two fuel lines going to it plus a vacuum line. Pull off the vacuum line and see if it there is any fuel present in the line. If so, the regulator is bad and must be replaced. Usually, a bad regulator is accompanied by a noticeable dark exhaust plume. A bad O2 sensor will keep the engine in cold (rich) startup loop and cause poor mileage but not as bad as you describe. If you smell raw fuel, the regulator is likely the problem.