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Old 01-11-2005, 12:59 AM   #1
DrtJnky
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Default Manifold pressure sensor

Does anyone know, for sure, what decisions the computer makes from the info the MAP sensor sends it. I do not think most mass air cars have a MAP and was thinking it is only used to regulate the stock boost control solenoid?
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Old 01-11-2005, 10:24 AM   #2
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Anyone ?????
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Old 01-11-2005, 10:31 AM   #3
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It uses it for boost control and fuel cut. I don't think it makes any fueling decisions based on MAP voltage, but it's possible it uses it to calculate the timing load zone? I dunno.
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Old 01-11-2005, 10:31 AM   #4
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limp home mode, ie bad maf sensor
overboost fuel cut

hth
ken
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Old 01-11-2005, 01:19 PM   #5
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boost measurement
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Old 01-11-2005, 01:37 PM   #6
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Most mass air cars, which is to say most cars, don't have a MAP because most cars are normally aspirated.
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Old 01-11-2005, 05:15 PM   #7
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The MAP sensor is located on the intake manifold just after the intercooler. Under normal conditions its output is used to feedback to the wastegate control solenoid. Under extraordinary conditions such as high speed, overboost, or MAF sensor failure it can be called upon to many things (fuel cut and "limp home mode"). I suggest the EcuTek forums if you would like to know more. Stephen or Ben can answer your question to any detail level you would like.

Why do you ask, maybe that is a better question for these boards?
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Old 01-12-2005, 03:34 AM   #8
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what the Adventage MAF over MAP for turbo car?
Save gas?
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Old 01-12-2005, 11:27 AM   #9
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In general MAP sensors are used on cars were the computer uses a speed/density map to make are fuel adjustements. MAF is Mass Air Flow, a sensor that tells the computer how much, how dense, and what temperature the air is. My two cents, Mass air motors react much better to modification, but the add a restriction to the intake. Speed density has no such restriction but requires the computer to do more " if X / Then Y" calculations to figure the cfm of incomming air.

I and the guys I work with are more old school. IE> Mustang 5.0/ Buick GN/ And the DSM Eclipse/Talon. I posed the question to them.....Why couldn't you remove the MAP sensor, install a pipe Tee, Put the sensor in the top of the tee and connect a MBC to the other end. Now you have adjustable boost with all the control of the ECU.
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Old 01-12-2005, 12:43 PM   #10
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john banks has done just that, iirc. he used bleed mbc.
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Old 01-12-2005, 04:27 PM   #11
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I don't think one is better than the other. MAP=speed density, they are synonyms. MAP based tuning is more flexible/adaptable to the addition of some parts. You don't have to worry about intake diameter or strange air currents in the intake. Large turbos don't max out the MAF senso, like so many of the Subys do.

I'm not sure why MAF based fueling is so popular. In the end you get the same information: the mass of air entering the engine. MAF is a more direct measurement of mass, but the sensors are very tricky (there are several kinds of MAF sensors). Perhaps at one time, computation power was limiting and MAF outputs a voltage that corresponds to mass. With that you would not need to calculate at all. MAP requires pressure, temperature, and volume to output a mass, but at the very least pressure and temperature must both be measured accurately and the density of the air computed--something a mechanical controller cannot do without a logic board.

Remember guys the Space Shuttle runs on the equivalent of a Commodore 64; we have come a long way fast.
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Old 01-12-2005, 05:53 PM   #12
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Quote:
Originally Posted by bboy
Remember guys the Space Shuttle runs on the equivalent of a Commodore 64; we have come a long way fast.


Apollo 11 used "the equivalent of 3 Commodore 64s" to get to the moon..."the Space Shuttle" now is a tad bit more equiped
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Old 01-13-2005, 12:40 AM   #13
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Mass air is so popular 'cause it tells the computer how much air is entering the computer. Speed density never really knows how much air is going into the motor it can only estimate based off air temp, man. vac or pressure, air temp. It then uses a set of base maps to do the calc. to cfm. These base parameters are why speed density systems, from the factory, are less adaptable then mass air systems. When you improve the whole system and more air gets into the engine mass air see's this, speed density still has to assume the base it was given.
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Old 01-13-2005, 02:18 PM   #14
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Speed density is no less accurate than mass air flow, it all comes down to the accuracy of your measurement devices. The idea that MAP based systems are less adaptable is just silly. Do you think Physics is voodoo?

The Space Shuttle's computer runs at 25 Hz (not MHz) and originally had 40K of memory that was eventually upgraded to 256K of memory. Five identical computers run the shuttle (redundancy in case one goes bad, and for processing). They have not been substantially upgraded since 1981, and they were adapted from IBM AP-101 computers originally designed in 1971. Commodore 64 is a pretty good match, better than a 8086-based computer which would seem like lightening.
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Old 01-13-2005, 02:29 PM   #15
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The biggest problem with a speed/density system (MAP) is that you need to know the volumetric effeciency of the engine at all RPM points and throttle angles. Changing anything which affects air flow will throw those VE maps off and make the ECU think it's getting less air than it really is.

Throw on that turbo-back exhaust and now your engine flows a lot more air than stock at the same intake pressures. With a MAP system the ECU will lean the engine out when it goes to closed loop fueling. With a MAF system, the ECU will see the additional air and compensate by adding more air.

That is the primary benefit of a MAF over a MAP system. The drawback is that MAF sensors are generally more fragile, expensive and restricts the intake tract more than a MAP sensor, although they are getting better all the time.
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Old 01-13-2005, 04:21 PM   #16
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Good summary, they both measure air and permit development of a starting tune (fuel and spark maps), albeit VE makes things difficult. Optimization is always an issue.
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Old 01-13-2005, 06:12 PM   #17
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I don't think I'll hijack this thread (whose value remains uncertain) by posting a link to a paper which describes the architecture of the flight director computers. I suspect that engine management geeks would also be interested to read how these computers operate.

The most fascinating aspect, in my opinion, is that the arbiter for the four computers "voting" outputs occurs at the actuator level. That is, each control servo receives all of the votes and discounts erroneous signals at the servo level. It's a brilliant and surpisingly simple solution. But can you imagine how expensive our cars would be if they used such a system?

http://www.research.ibm.com/journal/...ibmrd2001E.pdf
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Old 01-13-2005, 08:07 PM   #18
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Quote:
Originally Posted by MojoHand
I don't think I'll hijack this thread (whose value remains uncertain) by posting a link to a paper which describes the architecture of the flight director computers. I suspect that engine management geeks would also be interested to read how these computers operate.

The most fascinating aspect, in my opinion, is that the arbiter for the four computers "voting" outputs occurs at the actuator level. That is, each control servo receives all of the votes and discounts erroneous signals at the servo level. It's a brilliant and surpisingly simple solution. But can you imagine how expensive our cars would be if they used such a system?

http://www.research.ibm.com/journal/...ibmrd2001E.pdf
The shuttle now uses an AP-101S, that link is outdated. Thinks like the Pathfinder use bits from the IBM RS/6000.

Did someone say speed density? :loL:
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Old 01-14-2005, 12:15 AM   #19
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Quote:
Originally Posted by bboy
Good summary, they both measure air and permit development of a starting tune (fuel and spark maps), albeit VE makes things difficult. Optimization is always an issue.

Both systems do not measure air? Mass air measures air, Speed density calculates air? The vol. efficiency doesn't just make things difficult, its the whole show for Speed Density. Unless there is a piggyback or replacement computer you can not go outside the base map for VE. Mass air will go to the limits of the injectors, fuel pump, ect. That is why I said I believe Mass Air to be more adaptable.
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Old 01-19-2005, 03:39 PM   #20
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This was a good find, balance view of MAF vs. MAP based tuning:

http://www.wincom.net/trog/efi.html
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