What is in a MAP sensor?

[gdouaire]

I had a DOA MAP sensor for a 3.8, bought on ebay as a replacement, so I pried it open to see what's in it.

It's a minuscule surface mount chip with a vacuum port on it. The rest of the sensor is just an empty plastic box to match the footprint of the OEM sensors:

Closer look at the core circuit :

Then I looked through my things and found an original GM MAP sensor. Much different, the enclosure is filled with electronics and some gooey clear silicone covers everything:

Behind the white square, there's the actual sensor, not a diaphragm, something else very small and a bit dirty from years of use:

I don't think the aftermarket vs OEM work on the same principle at all.

I am not sure that the needle hole on the chip on the aftermarket sensor would be tolerant to dirt in the long run.

 

[69hurstolds]

Impressive. I've never pried one apart. Nice to see what's in them. Because of what you did, I would surmise that the OE sensors are likely more accurate, more sensitive to vacuum changes, and therefore, more beneficial to the car. Probably not worth the testing, but just the fact that so much more went into the production of the OE stuff, there must've been a reason for it.

 

[86 Salon]

The OE sensors are much better than the cheap sensors. I was at a GM training class back in the 80's and the instructor told us that there were seven circuits required to operate a HEI ignition module. He told us the a good Niehoff had 12 circuits. A GM module had over 2000 circuits. The extra circuits were there for circuit protection.

 

[64nailhead]

It’s a MAP sensor - not really
Complicated. Probably an updated pressure port.

 

[69hurstolds]

You got to know which type of sensor you need, kids. Typically, the V8 carb cars use a manifold differential pressure, aka VAC sensor under the hood + a barometer under the dash (same part number as a MAP sensor). The MDP sensor works opposite of a MAP sensor. With a MAP, as vacuum goes deeper, the output voltage to the ECM drops. With an MDP, the output voltage to the ECM goes UP when vacuum goes deeper. Their outputs are opposite of each other for the same vacuum signal. They both look exactly the same at 10 paces away. Has to be done by part number. DON'T TRUST THE AFTERMARKET LABELS. (Read the post in the link below for further info). GM stamps or inks at least the last 3 of the part number on the sensors themselves. Aftermarkets may, or may not. This is a problem if you don't know what you have.

OLDS Thread 'Olds School: 307 Olds V8 MAP sensor or MDP?'

Feb 6, 2022

Caveat- this is mainly for Oldsmobile 307s, to which I'm more familiar with than say, the 305 Chevy engine. I believe since they use the same sensors, they work the same, but I have done absolutely no further research on them, thus, if you know something different, please correct me where I'm off my rocker. Also, I do not claim to be an expert, but I've piddled around with emission equipment on G-body Oldses enough to feel confident I can troubleshoot the Olds emission stuff enough to keep my butt out of a bind.

NOTE: A MAP sensor is NOT an MDP sensor. Period.

One of the sneaky things...

• 69hurstolds
• Replies: 0
• Forum: Fuel / Air / Boost / Emissions

• 

I do have to add something, however. Some of the older MAP sensors that were used as BARO sensors under the dash for the gas V8 cars, had a foam sleeve "cover" that slid down over the plastic dog nut nipple on the BARO sensor port. It had adhesive on it to stick it to the base to keep it from falling off. This is very likely the only reason the 16006833 had a different part number than the MAP sensor under the hood. Otherwise they work the same. The foam was supposed to be a "cover" for the port since it just measured ambient air pressure. Like an air filter to keep dirt and junk out of the port. This foam must be the same foam used in headliner boards, because over time, it gets brittle and turns to dust when you touch it. Ask me how I know. Anyway, I was doing a google search and came up with this pic showing one still (sorta) intact! I've never seen one lately fully intact. Except for the one on the 85. I touched it and poof. Foam dust. The foam should cover the nipple end as well. When used as a BARO sensor, it just hangs out under the dash over by the ECM. And unlike the engine, the port is NOT connected to anything, obviously. It's just used as a reference signal for the ECM to compensate for surrounding ambient air pressure. So if you have one of these, and need to use it under the hood, just remove the foam before hooking it up to the vacuum tube. Ensure you suck any dead foam out of the tube as well with a vacuum cleaner or something. Later versions after 833 did not have the foam, since it was a MAP sensor part number anyway.

Also, briefly mentioned in the post, that they made 1 bar and 2 bar (1 bar = 14.7 psia) sensing MAPs for G-bodies. You need to ensure you get the right one, even if using it as a BARO. The output signal varies due to the pressure rating. Boosted cars, like the GN/Turbo Buicks got a 2 bar sensor. The gas/diesels got a 1 bar sensor. You MUST get the right MAP/BARO for your car. Again, it's easy to tell on the last 3 numbers of the part number stamped into the sensor on top of where the plug goes. This only applies to GM sensors. Have no idea about the aftermarkets.

Confused even more, yet?

The info below can help you decide. It's VERY important to not get the wrong one. Turbo Buick guys can probably attest to that. (Even the boosted LS guys use 3 bar or even 4 bar sensors, but they're different shapes and plugs, so no worries on making that mistake for your G-body.)

The last 3 numbers stamped on top of the plug port should tell you. 460 equates to 16017460. This is usually followed by the manufacture date. Last digit of year, then day of the year. 8= 1988 most likely, 267th day.

What nobody tells you, and you cannot tell by looking, is which part numbers are 1 bar, 2 bar, etc. Below can help. I only included p/n's that you would probably find and use. There's probably some more, but I'm too lazy.

1 Bar - 039 (16137039), 460 (16017460), 835 (16006835). You can also use the baro sensor 833 (16006833), but make sure to remove all remnants of any foam.
2 Bar- 886 (16009886), 012 (16038012), 539 (16254539), 241(12569241)
3 Bar- 749, 861 (included just to ensure you avoid using these on your stock G-body should you run across them)

 

[CopperNick]

Okayyyyy......... now me here at my normal level of confusion for a Monday Morning. The topic is MAP, meaning Manifold Absolute Pressure, I hope, and just to compare and contrast them here, how does that line up or compare with an MAF or Mass Air Flow Sensor? Two different sensors doing two different jobs according to their text book definition.

So where specifically in the manifold would the pressure sensor typically be installed to get the most accurate reading or is it just plugged into a port in the manifold to "sample" the varying values of pressure and transmit that data to its controller?

And while I am adding mud to the matter, wouldn't any change in Air flow based on either acceleration or deceleration cause both the MAP and MAF to alter the readings they are generating?



Oh yeah, be careful with the MAP acronym. Among other things it can stand for "Morning After Pill"!! (Hey, no lie here, google the acronym and just see the shear volume of possibilites for those three little letters)


Nick

 

[69hurstolds]

Okayyyyy......... now me here at my normal level of confusion for a Monday Morning. The topic is MAP, meaning Manifold Absolute Pressure, I hope, and just to compare and contrast them here, how does that line up or compare with an MAF or Mass Air Flow Sensor? Two different sensors doing two different jobs according to their text book definition.

So where specifically in the manifold would the pressure sensor typically be installed to get the most accurate reading or is it just plugged into a port in the manifold to "sample" the varying values of pressure and transmit that data to its controller?

And while I am adding mud to the matter, wouldn't any change in Air flow based on either acceleration or deceleration cause both the MAP and MAF to alter the readings they are generating?



Oh yeah, be careful with the MAP acronym. Among other things it can stand for "Morning After Pill"!! (Hey, no lie here, google the acronym and just see the shear volume of possibilites for those three little letters)


Nick

Depends on the system, but you're on track. I'm not an electrical systems engineer, nor do I claim to play one on TV.

A MAP sensor does not care what air flow into the intake is. It only senses absolute pressure of the intake manifold, hence the name, compares it to the reference voltage, and sends back a signal to the engine controller as an input. Constantly. The MAF measures air flow, turns it into an electrical signal, and sends that signal back to the computer as just another input to help the computer decide timing and fuel and egr adjustments, etc. Again, constantly. You would think a throttle opening, the MAP would sense a pressure rise (vacuum dropping) and the MAF would sense the air flow into the engine going up. These two signals (among others) are digested into the ECM or whatever computer system it's using it for, and the brain box determines if those signals are in the expected range with each other. Along with a zillion other inputs from the engine. If everything is in spec, it adjusts fuel/timing/egr/etc., as needed as it figures out what's what. It does it in a blink of an eye, in human time. OBD1 or II, or newer gets more complex as the generations evolved. Crude example: Computer expects ? amount of mass air flow at 30% throttle opening, and vacuum should be whatever at a certain rpm, at normal operating temperature. If those 3 inputs are what the computer compares and expects, everything is cool and it puts out whatever the brain says fuel maps and timing curves and whatever, should be. If the computer determines by those inputs the timing needs adjustment, then it adjusts timing to be whatever according to those conditions and abilities.

CCC components are like a baseball team. The manager is like the ECM. The players only concentrate on doing their own jobs well. They can't do much about what the other players are doing. The manager oversees the action on the entire field and constantly monitors and adjusts all 9 guys as neccessary as game conditions change. Guy on second base taking too big of a lead? Move the shortstop or 2nd baseman closer to the bag if it makes sense. Pull hitter at the plate? Instruct the catcher to tell the pitcher to throw the ball on the outside of the plate, keeping away from the batter's wheelhouse. Adjust, adjust, adjust as the inputs come in at real time. Of course, if a player falls down and is injured, doesn't do his job and allows too many runs, the manager throws a code (timeout) and a light flashes on the dash for YOU to do something about it. So you probably have a bad sensor and it needs to be replaced by a new part off the bench.

And yes, pressures and air flows change with the throttle position (which the computer also sees via the TPS). Constantly changing inputs, and constantly changing outputs to keep everything running inside the acceptable limits. If not, then after a bit of time, it'll toss you a code.

 

[Kra5379]

It’s probably a VAC sensor not a MAP sensor. They look identical on these but are not interchangeable because of the way they read and transmit data. In short a MAP measures absolute pressure and a VAC measures pressure differential. When you add vacuum to the MAP, the voltage signal to the ECM decreases, when you add vacuum to a VAC voltage to the ECM increases

 

[Clone TIE Pilot]

Okayyyyy......... now me here at my normal level of confusion for a Monday Morning. The topic is MAP, meaning Manifold Absolute Pressure, I hope, and just to compare and contrast them here, how does that line up or compare with an MAF or Mass Air Flow Sensor? Two different sensors doing two different jobs according to their text book definition.

So where specifically in the manifold would the pressure sensor typically be installed to get the most accurate reading or is it just plugged into a port in the manifold to "sample" the varying values of pressure and transmit that data to its controller?

And while I am adding mud to the matter, wouldn't any change in Air flow based on either acceleration or deceleration cause both the MAP and MAF to alter the readings they are generating?



Oh yeah, be careful with the MAP acronym. Among other things it can stand for "Morning After Pill"!! (Hey, no lie here, google the acronym and just see the shear volume of possibilites for those three little letters)


Nick

For Monte Carlos, they were either mounted on the passenger wheel well on earlier models or on the intake manifold behind the carb on later models. The Vac sensors had a vacuum line running from the sensor to a barb on the back of the carb next to the brake booster port. The Baro sensors were also not always under the dash, later Monte Carlos that had manifold mounted Vac sensors placed the Baro sensors on the passenger wheel well next to the ESC module. Each division had different layouts for the CCC system.

 

[doood]

looks like the OEM is a strain gauge (makes sense; voltage vs. deformation under pressure). Likely the replacement has a strain gauge too (miniaturized under the hole in the IC?).