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Thread: Diesel MAF sensor alternative...

  1. 22nd March 2012, 09:05 PM #1
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    DiscoJakes
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    Diesel MAF sensor alternative...

    Morning all

    I jokes the other day about making a cheap MAF sensor for the TD5. Now one of my friends dared me to put it in practice.

    So basically you have +12v feed, ground and then a 0-5v output back to the ECU.

    It must measure air flow, so plenty computer fans laying around....
    As is it gave me rough readings and only about 2.3v max.

    So the circuit now evolved with a cap and a zener diode to clip at 5v.
    Problem is still I don't get enough volts.

    So my Q is the following - can I use the fan's generated output to feed a LM317 opamp circuit using the +12v original feed?

    Any suggestions or help?
    thanks
    jakes
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  2. 23rd March 2012, 01:05 AM #2
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    DiscoJakes
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    Ok, one of brain buddies suggested that I would be better off using the 3rd wire from the fan. The PIC pickup and running a converter from the microprocessor. This will surely be more accurate but would add to cost.
    Still not a bad idea for a very cheap MAF sensor that will work...
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  3. 23rd March 2012, 03:48 PM #3
    Dougal
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    It'll give you a signal, but will it compensate for air density and how accurate will it be?
    Will the results be linear or quadratic?
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  4. 24th March 2012, 07:34 AM #4
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    The TD5 MAF sensor only does air flow.
    Density gets read from the AAP sensor, which also reads ambient air temp. On a side note high altitude compensation can be done via fooling the AAP sensor and increase fueling.

    Actually the TD5 ECU is quite happy when fed a constant 4.5v from the MAF sensor!!! Makes one think about spending so much money on sensors sometimes...
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  5. 24th March 2012, 08:57 AM #5
    Dougal
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    Is the stock MAF a hot film or hot-wire type?

    In the average diesel ecu of that era (I haven't been inside TD5 code) the MAF is used as another smoke limiter. If you feed it high voltage signal then in many conditions you won't notice the difference, your fuel will still be limited by torque limiters and boost pressure sensors.

    But I suspect there will be times the ECU is relying on the MAF signal more than others, in these situations you might find excessive EGT's or even smoke where you wouldn't with a working MAF.
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