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Thread: MAP sensor instead of MAF?

  1. #1
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    Default MAP sensor instead of MAF?

    Has anyone every looked at using a MAP sensor on our engines instead of a MAF sensor when upgrading to FI?
    -Mike
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    i'm not sure that its possible w/the stock ecu. if you run something like megasquirt its very easy,esp since we already have a seperate iat sensor.

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    What do we know about the Contique ECM's? Has any body ever studied the pin outs and what kind of software logic is being used and if it can be modified. I know the Honda guys have had pretty good success with this aspect of things.

    I guess I don't know the limitations of the SCT Xcal PRP either... If a guy were to look at the pin outs of the ECM and determine that there was an unused pin and a unused sensor power pin... I wonder if you could wire s MAP sensor in that way and then set it up to be monitored via the Xcal programming and use it as an input to determine your AFR.
    -Mike
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    you can find the pinouts on the old forum.

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    Do you mean switching to a speed density system as opposed to MAF? There's TONS of info on MAF vs SD in the mustang world...how you can translate it to the CSVT, I'm not sure, but it's a goo dplace to start looking IMHO.

    Good Luck!

    RJ


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  6. #6
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    Quote Originally Posted by tozovr View Post
    Do you mean switching to a speed density system as opposed to MAF? There's TONS of info on MAF vs SD in the mustang world...how you can translate it to the CSVT, I'm not sure, but it's a goo dplace to start looking IMHO.

    Good Luck!

    RJ
    Yea that's what I'm trying to do. Speed density likes boost more then MAF systems. Is there a particular Mustang site that you can point me to?
    -Mike
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  7. #7
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    What issues are you having? Speed density has more issues adapting to FI than than MAF systems.

    Here's an article on someone switching to a MAF setup because of issues with speed density: http://www.fordmuscle.com/archives/2...sion/index.php

    All the newer cars are MAF and the FI setups work fine as long as you tune the car correctly.
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  8. #8
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    Quote Originally Posted by Blackcoog View Post
    What issues are you having? Speed density has more issues adapting to FI than than MAF systems.

    Here's an article on someone switching to a MAF setup because of issues with speed density: http://www.fordmuscle.com/archives/2...sion/index.php

    All the newer cars are MAF and the FI setups work fine as long as you tune the car correctly.
    Yea that's what I've been finding. I've just heard that MAP sensors are better for FI, but apparently that's not necessarily true according to what I'm finding in my web searches...
    -Mike
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  9. #9
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    in the early 90's gm had maf sensors on 2.8 v6's. but they were cheap and unreliable. they had a bulletin out to switch to the speed density system since they had a map in place already the computer just relied more on that information and eliminated the maf reading. performance went down as well as fuel efficiency as a result. i was told then by a gm engineer that there is no substitute for the maf reading. he said it was a shame their maf's were so cheaply made! lol i don't know if that helps but it's interesting.
    95 Mystique Zetec ATX
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  10. #10
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    Speed Density is usually easier to calibrate for high HP combinations than Mass Air, but only because it is far more difficult to build and calibrate a MAF sensor that can for example precisely meter 0-1000 cfm (which would be necessary at or over 1000 hp) while outputting a 0-5v signal which must then have a corresponding calibration factor in the ECM. Speed density on the other hand merely needs a MAP sensor capable of reading the relavant pressure (multiple bar is not uncommon) and an ECM lookup table that has been scaled to include relevant operational pressure ranges.

    However, hardware capabilities aside (lets assume that we have capable hardware for our engine output goals) MassAir tuning is easier than SpeedDensity. For MassAir you input the MAF calibration info into the ECM, establish a series of AF ratios required for a variety of Load:RPM bins and the ECM is able to determine fueling requirements based on readings from the MAF, assuming settings are accurate fueling should be accurate. On the other hand, with Speed Density, the AF goals based on Load:RPM still need to be established, but one must establish a Volumetric Efficiency table (VE) for an individual engine or fudge it enough to work generically (OEM style). Furthermore, the SpeedDensity system will only accurately compute fueling needs when the VE table is properly established for the engine which means running it though all the operational areas (on a dyno preferably) and manually adjusting the VE table.

    Either way, closed loop operation (especially with WB) simplifies matters slightly in that the ECM is able to compensate for diminished precision as components age, for estimations made during mass production, or compromises made during tuning. Self adapting (learning) systems aid in keeping everything happy as well, but either/both of these adaption methods are tuning assistants and not replacements for precision tuning.


    Speed Density systems can be every bit as fuel efficient as Mass Air, but only when the lookup tables (VE specifically) are tuned to accurately reflect the demands of the engine being controlled and are adjusted over time to reflect changes in engine demands with age.

    The biggest hurdle that must be overcome with the majority of Mass Air systems is that the end user is retuning a factory ECM to provide fueling control during conditions never anticipated by the original programming. This results in caps on how far a factory ECM can be manipulated to continue providing fueling. Factory ECM's tend to have hardware and/or firmware limits on how advanced and how precise they can function; at some performance point you reach a limit on how far you can push a factory ECM.

    All that being said, most (if not all) Mass Air systems resort to open loop direct fuel look up bins at high load (WOT operation) which can often be scaled to cover extreme operation areas otherwise beyond the ECM's capabilities by dyno tuning and manually telling the ECM how much fuel to spray.
    Last edited by Pope; 02-13-2008 at 03:00 PM.
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