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TD5 MAF Bypass Mod?

Discussion in 'TD5' started by bankz5152, May 27, 2018.

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  1. bankz5152

    bankz5152 Well-Known Member

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    Been looking at AJS Tyres race 110s which are very impressive to say the least! Ones pushing 240bhp :eek::eek:

    I noticed one of them is using a MAF bypass whicb was mentioned on here a week ago or so.

    Looks like you plumb a 20mm hose into the clean side of the airbox and introduce it after the MAF in the intake pipe or through the DCV. Which in theory should allow some air to bypass the MAF and reach the turbo without sending the MAF out of range and messing with things.

    Video


    Pics from AJS, bit more advanced than something I would do but you get the idea.

    29512609_1804864342907901_6322181902039635414_n.jpg 29512853_1804864469574555_7344183828943352817_n.jpg

    Anyone got any experience or comments on this?

    Reason behind it is my 110 is highly tuned and with the MAF plugged in it doesnt lile the top end, tends to kangeroo and loose power. Tried two genuine MAFs with the same result. According to both BAS ans TD5inside it is down to the MAF going out of range and confusing the ECU so its been left unplugged.
     
  2. sierrafery

    sierrafery Well-Known Member

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    That air flow bypass mod is a bad ideea IMO, the MAF readings will be lower on the whole curve than the reality which can mix up the management worst than with it unplugged and increase the EGT, the correct way is to modify the air flow chart in the fuel map as the upper limit to be 800kg/hr but if you dont want to pay for that it's better to clamp the voltage on the MAF at 4.6V at least the ECU will get correct readings untill the top just that the output will not exceed 680 then... any skilled electronist should be able to make you such clamp and should not be as expensive as a boost box which is the same kind of circuit, i couldn't find this kind of limiter in UK https://splitsec.com/product/vc3-100-voltage-clamp/
     
  3. bankz5152

    bankz5152 Well-Known Member

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  4. sierrafery

    sierrafery Well-Known Member

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    IMO that device would also alter the whole curve which i dont like
     
  5. bankz5152

    bankz5152 Well-Known Member

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    What do you mean by alter the whole curve?

    Surely the MAF would read the maximum it could flowing through it, the turbo then gets that air plus more fed through it and the MAP compenstates accordingly?

    I didnt even know the MAF max limits could be altered within the ECU never seem such a service advertised.

    How does the voltage clamp help?
     
    Last edited: May 27, 2018
  6. sierrafery

    sierrafery Well-Known Member

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    The MAF is calibratd from factory to give a voltage output between 0 - 5V according to the air mass aprox as in the attached graphic, when the air mass gets to 680kg/hr then output is close to 4.7V where the ECU cuts fuelling to protect the turbo from overspeed, bypassing the flow with a pipe or using a ''corrector" like that from the link will give to the ECU a false reading so the real air mass will be differentt than the one calculated by the ECU... a voltage clamp will let the curve to be exactly the same so the air mass calculation will be real just that when it gets to the upper limit it will stay there not exceed that voltage like it happens now.... the MAP doesnt compensate anything which is MAF related, it simply measures the boost level... a voltage clamp on the MAF is the same thing like a boost box for the MAP which doesnt let the ECU get higher reading than the overboost limit regardless of the real boost

    MAF output graph.jpg
     
  7. bankz5152

    bankz5152 Well-Known Member

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    Ahhhhhhhh ok that makes sense. So the voltage clamp, stops the MAF from reading above 5v and just keeps going as opposed to hitting 5v (or the max value) and telling the ECU and cuttjng fuel
     
  8. sierrafery

    sierrafery Well-Known Member

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    It stops the MAF from reading above the cut-out limit cos the MAF won't give higher output than 5V anyway just that the cut-out limit is below 5V around 4.6 or so i dont know exactly how much
     
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  9. bankz5152

    bankz5152 Well-Known Member

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    Cool. Ill see if my mate can knock one up for me and install it :)

    Simply case of tapping into the MAF plug?
     
  10. sierrafery

    sierrafery Well-Known Member

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    Yes
     
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  11. johnlad

    johnlad Well-Known Member

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    Bell auto services sell the maf clamp, as already stated it wires into existing maf connections, simple fit
     
  12. sierrafery

    sierrafery Well-Known Member

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    that BAS clamp is not available anymore, also any device like these(boost box included) are way to expensive for what they are, the clamp is doable with a zener diode and a resistor max 1 quid each
     
  13. johnlad

    johnlad Well-Known Member

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    Yes but not everyone has the technical ability to build there own maf clamp
     
  14. bankz5152

    bankz5152 Well-Known Member

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    True.

    I wonder by BAS stoppes selling them, seems unusual.
     
  15. johnlad

    johnlad Well-Known Member

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    I think if you give them a call they’ll sort one out for you
     
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  16. sierrafery

    sierrafery Well-Known Member

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    I revive this post by quoting myself and i must apologise for the above statement as even if in theory is logical in reality it's not the best solution cos the voltage drop on the circuit wwhen the extra voltage is drained alters the end of the signal curve... i tried. it works but i'm not pleased with the result cos it's too ''raw'', since then i became wiser and i can say that the attached scheme works well and IMO that's what it is in the BAS or other devices... though the overall cost of components doesnt exceed 10 quid, i described exactly which wire where to be connected, pins 1.2.3 are at the MAF's connector only one comes from the AAP cos it's the closest 5V source

    MAF cut out limiter.jpg
     
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  17. MJI

    MJI Well-Known Member

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    Not sure on this what I need to buy.

    I am pretty good with a soldering iron, but not an expert at electronics like you.

    Case of tell me what to do and I can do it. My most complex job was fitting a NICAM decoder to a HiFi Video Recorder so I could record stereo broadcasts.

    I have an account at RS components.

    But I can work from the above diagram for wiring.
     
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  18. MJI

    MJI Well-Known Member

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    I do get the occasional too much air flow warning on full throttle
     
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  19. Anton88

    Anton88 New Member

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    I’d be very interested if you could make me 1 and I’d pay you for you it, it’s alittle bit beyond me to make one thanks
     
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