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Disabling EGR

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by dieselman, Jul 4, 2010.

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  1. dieselman

    dieselman Senior Member

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    In general it's felt that having the EGR (exhaust gas recirculation) system on diesel engines is good for reducing the NOX output but bad in all other respects.
    It reduces economy, creates more smoke, increases problems and maintenance requirements due to clogging the intake and can reduce overall engine life.
    As a result of wanting greater economy I decided to stop the exhaust gas being recirculated. The problem with doing this on a modern engine is that the EGR valve operation is monitored by the MAF sensor.
    The only way to disable the EGR and not trip a fault code and limp home mode is to fool the MAF into thinking the EGR is still working.

    On another forum I saw a member Karteck was also looking into this and performing some testing on what resistance values to use to create the required drop in MAF output when the MAF should be operating. He provided the below circuit to use.

    The basic circuit for this comprises of two resistors to act as a potential divider and a diode to stop 12v being fed into the MAF circuit.

    By connecting into the EGR vacuum transducer activation wire this causes the circuit to only operate when the transducer should be operating the EGR valve.

    The standard circuit is a 1k ohm resistor, a 470 ohm resistor and a diode. 1/4 Watt resistors work OK.

    [​IMG]

    The above is for a W210 300TD but the same components should suffice for most applications, but the connections will need to be determined.

    First locate the EGR vacuum transducer and disconnect the wiring plug. Using a meter check which wire is the 12v feed and which is the active low signal wire.

    [​IMG]

    Next go to the MAF sensor and again using the meter source the signal wire, which should be Pin5.

    For ease of connection trace these wires back to the engine ECU. The easiest way to do this is to disconnect the connector, remove the screw in the back of the connector and prise the connector apart to reveal the wires.
    In practice removing the screw and operating the over centre catch will part the connector.

    [​IMG]

    Build the circuit and insulate the components then after locating the appropriate connections (12v, EGR active low, MAF signal) strip the insulation from the wires and solder the mod in place, then make good the insulation.
    You will need to disconnect the EGR transducer electrical connection, so ensure you tape it up to stop any water ingress.

    The final installation will look something like this, although normally the wires are tucked away by the side of the loom.

    [​IMG]


    The next diagram is for a ML270 just to show the connections. It's the same components, just different ECU connections.

    [​IMG]

    W210 300TD is:

    Switched 12v (sorry, can't remember which pin I used)
    EGR signal = Pin 35
    MAF signal = Pin 21

    ML270 CDi:

    12v = Pin 37, plug 3
    EGR signal = Pin 60, plug 3
    MAF signal = Pin 24, plug 4

    I think the above will work for all Vacuum transducer type EGR valves, but the connections may vary.

    if you try this mod please report back your connections.
     
    M Z likes this.
  2. turbopete

    turbopete Senior Member

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    isnt it easier to just blank it off?
     
  3. OP
    dieselman

    dieselman Senior Member

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    Won't work. As mentioned, it will throw an error code and Limp Home mode.;)
     
  4. turbopete

    turbopete Senior Member

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    so i can only assume that somehow the maf knows how much is being recirculated by the egr somehow? surely the maf is at the intake though and the egr connected more directly to the manifold, for heat purposes if nothing else?
     
  5. OP
    dieselman

    dieselman Senior Member

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    The EGR operation is indeed monitored by the MAF.

     
  6. turbopete

    turbopete Senior Member

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    so surely the flow from the egr would have to go through the maf wouldnt it? and surely the gases would be too hot for the maf to withstand? or am i missing something?
     
  7. Naraic

    Naraic Moderator

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    Its's monitored electronically.
     
  8. OP
    dieselman

    dieselman Senior Member

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    The MAF is in the cold intake the EGR enters further downstream. the MAF then monitors the reduced cold intake when the EGR valve admits hot recirculated gas.
    The biasing circuit drags the MAF voltage lower when the EGR signal line goes low.
     
  9. oigle

    oigle Senior Member

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    Well done dieselman. Was hoping you might do this. As you were the initial source of info on this shunt, you were logically the man to do it.
    I hope now that the mods place this in the "sticky" area as there are a lot of people that can benefit from this modification.
    Good finale to the long thread on the subject.
    Well done.
     
  10. soup nazi

    soup nazi Senior Member

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    DieselMan
    Thanks for the photo's. I took a look at my 2003 ML 270 yesterday and noticed the following differences;

    The wire from MAF pin 5 to the ECU Pin 24 plug 2 is Brown/White.

    The return wire from the Vacuum Transducer to ECU goes to Plug 3 pin 50 is Grey/Black. (there is no pin 60, it only goes to 52. Easy to mistake I initially read it as 62)

    The 12V Red/Grey from ECU Pin 37 plug 3 is correct.

    I am counting the plugs with the one closest the engine being number one as they have numbers on the plugs.

    I will do the mod soon and will post photos etc on the other original thread. Well done for doing the work on the design its more involved than some might think. I just wish the same existed for my dads VW Mk 5 Golf Tdi.
    SN
     
  11. alexanderfoti

    alexanderfoti Moderator

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    doesnt the maf detect the lower pressure when the valve is opened?

    Also TOP NOTCH info! saved me masses of problems/money! Thanks
     
  12. oigle

    oigle Senior Member

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    As I didn't personally do the job or look at the wiring involved, I took the details provided by my leccy. He was probably not as careful as he should have been in writing them down. I understand transposing grey with green as he wrote Gr to start with. The others - I don't know. Plug numbers differences may be as a result of counting from different ends.
    As Daryl has personally inspected the wire colours etc., I am quite happy to go with the colours etc nominated by him. Maybe alexanderfoti might like to confirm as he personally did his too.
    Really, all said and done, the wire colours at the afm and transducer need to be confirmed anyway with each individual vehicle and then located in the ecu wiring loom. The 12v source seems to be undisputed. On that basis, any model can be modified, using the shunt diagram as provided by dieselman.
     
  13. OP
    dieselman

    dieselman Senior Member

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    It would be best if you post your Mod back into this thread so all the EGR mods are together, unless you would rather not.
    Why not apply the same mod to the VW Golf, the same principles apply. I intend to do it to our VAG car when I get time.

    So it appears there is another configuration for the ML 270. It indeed appears that every car is going to need to be diagnosed separately to any other as the wire colour and ECU pins change.
    Thanks for the feedback.:)

    The wire from MAF pin 5 to the ECU Pin 24 plug 2 is Brown/White.

    The return wire from the Vacuum Transducer to ECU goes to Plug 3 pin 50 is Grey/Black.

    The 12V Red/Grey from ECU Pin 37 plug 3.
     
  14. wemorgan

    wemorgan Senior Member

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    Very good write-up Will, thanks. Do you have an estimation of the mpg gains this will make? Also, would you anticipate any issues come MoT time? (which gases do they measure on diesel cars?)
     
  15. television

    television Always remembered RIP

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    This excellent mod should not be detected on a MOT test as the EGR valve does not open at idle
     
  16. OP
    dieselman

    dieselman Senior Member

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    It does on a diesel as that's when the EGR is most required to reduce the free oxygen so reducing NOX output.

    Removing the EGR should reduce particulate output so should possibly improve the smoke test reading.
    The Citroen is pre EGR and the official mpg rating is 2mpg better than the same car equipped with EGR.
     
  17. television

    television Always remembered RIP

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    When I get a diesel SL I will get better ;);)
     
  18. OP
    dieselman

    dieselman Senior Member

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  19. television

    television Always remembered RIP

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    Thanks and that explains well what you are up to,, and I am a little bit wiser :D:D
     
  20. S.Speed

    S.Speed Senior Member

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