What is in a MAP sensor?

CopperNick said:

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?


Nick

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64nailhead said:

A MAP and MAF sensor are doing the same thing - basically. Meaning they are supplying data to the ECM so that ECM can determine how much fuel to add via a 2 axis table with one axis being RPM and the other being the MAP or MAF reading. A MAF sensor reads the actual amount of air being ingested, where as a MAP sensor makes an assumption. Both use feedback from an O2 sensor to make fine tuning trims onto the AFR (emissions). Both have advantages and disadvantages. A MAF sensor is more precise than a MAP sensor, hence the reason that all modern vehicles use a MAF rather than MAP sensor.

The MAP sensor has to have it's manifold source somewhere downstream of the throttle plate(s) and MAF sensor has to be upstream of the throttle plates. Both are are supplying an input voltage that is calibrated to the ECM that is in use.

During accel and decel there are other settings in the ECU to adjust the fueling and spark. Look at the two pics attached. These are using a 4 bar MAP sensor - 1 bar = 14.7 psi. So -14.7 to 0 psi is 1 bar, then 0 psi to 44.1 is 3 bar. Add them together to get to 4 bar. The line (trace) on the non-colorful pic shows what part of the table is being used during a WOT pass at 30lbs of boost.

FWIW, this table is doing nothing more than mimicking what a carburetor is doing. The accel and decel are the squirters and accelerator pump lol. And the timing tables are doing the same as a stock HEI with vacuum advance has done for 50+ years. Don't be intimidated by a sensor, table or ECU. It's using the same info everyone has used since carbs and dizzies have been in use.

Click to expand...

64nailhead said:

A MAP and MAF sensor are doing the same thing - basically. Meaning they are supplying data to the ECM so that ECM can determine how much fuel to add via a 2 axis table with one axis being RPM and the other being the MAP or MAF reading. A MAF sensor reads the actual amount of air being ingested, where as a MAP sensor makes an assumption. Both use feedback from an O2 sensor to make fine tuning trims onto the AFR (emissions). Both have advantages and disadvantages. A MAF sensor is more precise than a MAP sensor, hence the reason that all modern vehicles use a MAF rather than MAP sensor.

The MAP sensor has to have it's manifold source somewhere downstream of the throttle plate(s) and MAF sensor has to be upstream of the throttle plates. Both are are supplying an input voltage that is calibrated to the ECM that is in use.

During accel and decel there are other settings in the ECU to adjust the fueling and spark. Look at the two pics attached. These are using a 4 bar MAP sensor - 1 bar = 14.7 psi. So -14.7 to 0 psi is 1 bar, then 0 psi to 44.1 is 3 bar. Add them together to get to 4 bar. The line (trace) on the non-colorful pic shows what part of the table is being used during a WOT pass at 30lbs of boost.

FWIW, this table is doing nothing more than mimicking what a carburetor is doing. The accel and decel are the squirters and accelerator pump lol. And the timing tables are doing the same as a stock HEI with vacuum advance has done for 50+ years. Don't be intimidated by a sensor, table or ECU. It's using the same info everyone has used since carbs and dizzies have been in use.

Click to expand...

What's The Difference Between MAF And Speed Density Setups?

Mass air flow and speed density are the two most common means of measuring how much air is being sucked into an engine, but what’s the difference?

www.carthrottle.com

doood said:

I recall the MAF from my LM7 has an internal IAT, and there is still a MAP on the intake. I replaced all my sensors before I put the motor in the Monte. I recall the Holley aftermarket ECU use something called 'speed density' whereas the stock LS1/LM7 ECU accomplishes the same with MAF. Apparently, speed density is the way to go when you don't want a MAF in the way of the feed hole (signal pegged upscale) in a 9s white Monte doing the g-body shuffle with a 500lb/hr fueling rate. If you have a somewhat normal car, the MAF is the way to go.

What's The Difference Between MAF And Speed Density Setups?

Mass air flow and speed density are the two most common means of measuring how much air is being sucked into an engine, but what’s the difference?

www.carthrottle.com

Click to expand...

doood said:

I recall the MAF from my LM7 has an internal IAT, and there is still a MAP on the intake. I replaced all my sensors before I put the motor in the Monte. I recall the Holley aftermarket ECU use something called 'speed density' whereas the stock LS1/LM7 ECU accomplishes the same with MAF. Apparently, speed density is the way to go when you don't want a MAF in the way of the feed hole (signal pegged upscale) in a 9s white Monte doing the g-body shuffle with a 500 1100lb/hr fueling rate. If you have a somewhat normal car, the MAF is the way to go.

Click to expand...

69hurstolds said:

When you're dealing with a factory ECM, it's looking to control the leanest burn possible to pass emission standards, while delivering acceptable drivability and performance across the RPM range. It was really an EPA thing. The aftermarket ECU's are far more tuneable for sure. But they all do pretty much the same thing. Get the most power out of each drop of fuel and control the entire thing within its bandwidth. Either way, ALL the sensors need to be doing their jobs so the brain can figure out if adjustments are needed and how to make those adjustments if needed.

I'm going back to my 4th gen Camaro days here, but there were definitely some LS1/6 cars that came with a MAP (back of the intake) and a MAF. As mentioned, the IAT was part of the MAF on later LS cars, but some earlier LS cars used a separate MAT (manifold air temperature). IIRC, the MAP was used for altitude adjustments, helped in ignition timing, and it saved your butt on speed density if the MAF junked out. I could be wrong, as I haven't studied the 4th gen F-bodies in a good while.

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