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GM 3-bar map sensor

Discussion in 'Forced Induction' started by Cashizslick, Feb 14, 2004.

  1. Cashizslick

    Cashizslick !i!i!i!i!i!i!i!i!i!i!i!

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    So, when i turbo my car, can i use a GM 3-bar map sensor instead of a missing link???

    If the answer is no, tell me why not lol.



    - thanks in advance, cash
     
  2. Loco Honkey

    Loco Honkey Banned

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    Read a few posts down about why you NEED a missing link when using an FMU.
     
  3. pissedoffsol

    pissedoffsol RETIRED

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    Honda's have a 2-bar map sensor. 1 bar (14.7xxxx psi) roughly equates to 1 atmoshphere, or the enviroment in which we live in.
    that leaves roughly 1 bar left for postivie boost....

    but the 2-bar, is really less than 2 bars.

    obd0, will max out at 9.4 psi at 0 elevation.
    obd1/2 will max out at 10.65 psi at 0 elevation.

    anything more than that- it simply CAN'T read it- REGARDLESS of what voltage its putting out.

    the 3-bar, is, well, 3-bars... which will give you about 25-26 psi as the max boost level, give or take your elevation.

    but, since it still operates on voltage, it will not work properly with a stock honda ecu.

    for example (just numbers out of my head)
    .5 volts on a 2-bar will read 5 psi.
    .5 volts on a 3-bar will read 8 psi.

    more so, it works the opposite way- sending a psi reading as a voltage to the ecu. if its sending the wrong voltage, the ecu will send the wrong amount of fuel to compensate-regardless of fmu's, injectors, and so forth.

    here we are, once again- Fuel Management.

    That's why you can't use a 3-bar "sucessfully" with a stock honda ecu and some check valves.

    The missing link is a check valve. It's goal is to block nearly ALL positive boost pressure to the honda map. Even though it can READ 10-ish psi, the ecu will throw a map code at 2-3 psi, because it simply doesn't know what to do with it. It wants to see vacuum- not boost. And, rightfully so, as our hondas are N/a, and the ecu's are not equipped to handel boost, and thus, don't know what it is.

    This is bad. basically, you're tricking the one thing that monitors your motor- the ecu. it really has no idea whats going on, and leaves it up to you to set it up properly.
    That said, a small setup with an fmu and a check valve, is perfectly fine for low boost applications. There isn't a huge gain, and thus, not a huge power level nor need for much additional monitoring to take place.

    The next step up is the VAFC hack.
    It doesn't use a check valve.
    However, the concept is the same- trick the ecu.
    by running way too big injectors, and tuning them with the vafc to say -30%, in effect, you are altering the map sensors output voltage reading to the ecu by -30%. this is called a piggy back. It takes a REAL reading from the REAL sensor, controls it, and then sends a flase reading back to the ecu. Once again, this relies on you to set it up properly, and limits the control of the ecu itself.

    Enter hondata, standalones and so forth. by chipping the ecu to have boost functions, our formerly N/a ecu can suddenly read, interpret, and return results. Taking it a step further, we can tune said ecu to work for our exact setup.
     
  4. highlife

    highlife Senior Member

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    another easy answer is IF u use a stand alone system etc.."hondata,Aem EMS" then u dont need the missing link.

    ppl tend to use te missing link with FMU/FCU
     
  5. d2149

    d2149 Member

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    somewhat off topic, GM is notorious for fucking up their map sensors. It took me 3 attempts at buying a GM 3 bar sensor to get one that worked. First time they gave me a 2bar, second time was just plain defective. That's what you get with GM.
     
  6. Cashizslick

    Cashizslick !i!i!i!i!i!i!i!i!i!i!i!

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    Hey thanks guys, very informative.
     
  7. pissedoffsol

    pissedoffsol RETIRED

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    the one you want is from the 89 trans am turbo (3.8 v6 turbo like the buick gran nationals.)
    the buick, is a 2-bar, as are all the rest.
    only the 89TA is a 3-bar.

    GM Part# 16040749
    however, it is out of stock and out of production.

    no fret- they have released a re-issue, which was not standard equipment...

    New GM Part# 12223861

    go here: http://www.gmpartsdirect.com/

    and enter in the part numbers in the block to view the part.
     
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