MAP Sensor Does What?

Discussion in 'General Tech Talk' started by hombre, Mar 3, 2008.

  1. hombre

    hombre .020 Over

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    Here's what I've learned so far... feel free to educate me if I've left anything out. :eek:

    Basic fuel delivery to the engine is determined by the MAP sensor and RPM signal. The Throttle Position sensor and Baro Sensor support these two. The MAP sensor takes the place of the power valve in a carburetor and vacuum advance diaphragm on a distributor. When engine load is high, the fuel injectors remain on longer. The sensor ignores the signal from the O2 sensor under high load. You can cause the mixture to go very rich by disconnecting the vacuum supply to the MAP sensor... the engine will run extremely rich. The ECU also retards the timing under high load.

    The MAP sensor controls the Acceleration Enrichment Tables in the ECU. Acceleration Enrichment is additional fuel used to improve throttle response, much like an accelerator pump on a carburetor. This fuel is applied in response to a positive throttle position rate of change or a positive manifold pressure rate of change. The resulting increase in manifold pressure can cause some of the fuel in the intake runners to undergo a phase change from vapor to liquid. Some of the liquid fuel can coat the walls of the intake runners instead of flowing into the cylinder. If additional fuel is not supplied to offset this effect, the engine will experience a lean condition.

    If you disconnect the MAP sensor vacuum line, problems can include detonation, power loss, stalling, rough idle, and poor fuel economy. With a disconnected MAP sensor vacuum line, the ECU "sees" high load. It compensates by lengthening the fuel injector pulse width and retards the ignition. So if you then re-tune the engine with a disconnected MAP sensor, you no longer have "load" info going to your ECU when you need it. This will result in a loss of performance, and in the worst cases... burned pistons. The only way to compensate for this is to tune an engine with a disconnected MAP sensor way too rich... not for performance. Most supercharged R3 riders don't notice the lack of performance because they are comparing it to their naturally aspirated experience... and don't have digital A/F indicators.

    A supercharged R3 can be re-tuned to run smoothly with a 2 bar MAP sensor. Is it perfect? No... ideally when installing a 2 bar MAP sensor on a 14psi boosted engine, you should tell the ECU the new MAP sensor parameters. Like this...

    [​IMG]

    IMO, this is the option that is needed in the TuneBoy program... not a MAP sensor delete button.
  2. Pig9r

    Pig9r Turbocharged

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    This post carries the same disclaimer
    The way I understand it is that the Rocket is speed density FI at small throttle openings only (up to 7%). Speed density uses MAP sensors and RPM to determine volumetric efficiency. The baro sensor takes a reading at start up to determine the ambient pressure, then the difference between the ambient pressure read and the MAP sensor helps calculate air density. Since air density changes with temp, there is also an intake air temp sensor. This info determines engine load and is referenced with engine speed. Since there is no MAF sensor, the amount of air entering the engine can't be determined. The a/f map is referenced based on the calculated load and the injectors are pulsed with the prescribed amount of fuel accordingly. The O2 sensor trims fueling where directed in the a/f map, (also at smaller throttle openings.) There is also a knock sensor to retard timing when detonation occurs.

    From throttle openings greater than 11% it relies on throttle position and engine speed to determine load. MAP sensor readings aren't referenced here.

    The ECU will interpolate between both of the above when the throttle position is between 7% and 11%.
    Last edited: Mar 3, 2008
  3. hombre

    hombre .020 Over

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    Good addition, Brian... the MAP sensor becomes irrelevant after 11% throttle (except when changing altitude). But nearly all "cruising" is done at less than 7% throttle... so most acceleration will begin within MAP sensor functional range. If there is no MAP sensor (as in disconnected), there will be no acceleration enrichment.

    If the R3 has a knock sensor, I sure would love to know where it is... that would make timing improvements way easier. Have I missed it in the manual? :confused:
  4. Pig9r

    Pig9r Turbocharged

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    I think you are right. I assumed that since it is OBDII it had a knock sensor, but it doesn't appear to be that advanced.
  5. Pig9r

    Pig9r Turbocharged

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    Where does you intake air temp sensor go with your SC setup?
  6. hombre

    hombre .020 Over

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    That's one reason I bought the dyno... to "see" the detonation and make timing improvements to my IC supercharged tune. Timing changes with step testing scared the pants off my former dyno tuner... no confidence. I believe the MAP sensor also retards the acceleration timing on the R3... so IMO with a disconnected MAP, "sweet spot" timing would not be possible.

    You're sussing out another of my HP tricks, aren't you? With the standard SC the IAT sensor has to go upstream of the supercharger... otherwise the temp of the compressed air will max out sensor. But with the intercooled version the IAT can go where it will actually do some good... just before the throttle bodies. The intercooler keeps the compressed SC air within IAT limits.
  7. HeR3tic

    HeR3tic Turbocharged

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    Map value and TPS value corrections - how do I do that

    That is all well above my head. I'll need more time to digest it all. But, the point about "most cruise speed are a 7% (below the 11%)" is pertinent towards my present inquiry. Hence, upon acceleration I have a momentary starvation in at least one cylinder. The map values for #1 and #2 are consistently equal. But number #3 is consistently lower by a value of approximately 30 or 3.0 depending on which TB screen I'm looking at. Dash values read 480 480 and 457 while sensor values appear with a tenths value (48.0,48.0,45.7). Am I looking in the correct direction at a possible cause for my ills and how do I correct this??

    Second to that is the TPS value indication as .680. I'm looking for a link herein that lead to the correction steps. If I understand it correctly this value should be .600 volt??? I believe I've got a handle on what mechanism(s) may require manipulation but verification would be appreciated.
  8. Pig9r

    Pig9r Turbocharged

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    Perhaps balancing the throttle bodies and resetting the TPS would help.
  9. hombre

    hombre .020 Over

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    HeR3tic

    I assume you have TuneBoy and know how to connect it. If you open TB Diagnostics and go to the sensors page (bike on, not running)... read primary TPS voltage. Adjust it by loosening the screw and VERY SLIGHTLY turning sensor one direction or the other. You will find that the sensor is EXTREMELY SENSITIVE, and that you have to recycle sensor page to get updated TPS voltage reading. To get around this, click re-set ISCV at bottom, and TPS voltage will go "real time" ( but still sensitive). Dialing the correct voltage can be frustrating given the sensitivity, and will even change when tightening screw. But keep at it, and you will succeed. Then follow instructions at bottom of page to re-set ISCV as well.

    I agree with Brian, that your TBs probably need balancing. Remember they are all set on #1, and that if you use TuneBoy to balance, the sensor page does not provide an instant (realtime) data update. You may have to refresh sensor page to read change. I personally think a good throttle balance tool like TwinMax is easier.
  10. HeR3tic

    HeR3tic Turbocharged

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    Awesome help! thanks gentlemen. the detailed info Hombre IS appreciated. I'd have twisted it a quarter turn :p good input! That puts me in mind of adjusting the distributor on a VW.
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