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MAF Delete (CDI 2)

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by stumo, Nov 19, 2019.

  1. stumo

    stumo Senior Member

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    Your Mercedes:
    ML270CDI 2002 facelift| Sprinter 316CDI 2003 LWB
    NOTE: This only works if you have the EGR delete already done from here:
    https://forums.mercedesclub.org.uk/index.php?threads/disabling-egr.68928/.
    (It could be made to work if you still have EGR, but you may need to put a 470 Ohm resistor between MAF pin 5 and EGR PWM signal at the ECU end.)
    • Are you sick of going into limp home mode all of the time?
    • Are you having trouble finding a genuine MAF sensor amongst all the fakes?
    • Are you burning through expensive genuine MAF sensors at an alarming rate?
    • Then you've come to the right place!
    I decided to try this mod after a spate of early failures on genuine Pierburg MAFs on some ML270s I maintain. New genuine MAFs here cost $250 a pop, and the best I was getting out of them was 6 months.

    But this simple circuit emulates a MAF just fine on my ML270 (and presumably other CDI2 based vehicles as well). All you do is connect a 5k6 resistor and a standard diode in series, between the 5V Reference pin and MAF signal input pin, at the MAF sensor connector (pins 4 and 5 respectively). Then you just leave the MAF sensor unplugged.

    The way it works is that it provides a valid MAF signal to the ECU. The MAF signal pin is a high impedance input to the ECU, so a tiny current flows from the +5V pin, through the resistor, then it gets dropped by about 0.7V by the diode, then the ECU sees about 4.3V on the input. This voltage corresponds to a ECU MAF reading of about 540mg/Hub using star diagnostics. This is at the top end of the range expected by the ECU depending on air temp and barometric pressure.
    20191106_140506.jpg


    This allows the ECU to run without any restrictions due to the MAF reading.

    When EGR is activated, the EGR delete circuit comes into play... Now the 20mA or so current flows out of the +5V ref MAF pin, through the resistor, and through the diode, where it gets read by the ECU again, but this time there is a 470 Ohm resistor there from the EGR delete circuit which pulls down the voltage via the ratio between our new 5k6 Ohm resistor and the EGR delete 470 Ohm resistor. This results in a MAF reading of around 200mg/Hub. This reading tells the ECU that the EGR is working as expected and prevents EGR faults from being logged.
    20191106_124114.jpg
    20191106_124137.jpg


    This is the entire circuit, simply plug it into your MAF loom connector and buy yourself a beer or two with the $250 you just saved.
    Capture.PNG


    I made mine so that the legs of the components were shaped and soldered like the pins on the MAF sensor, so they fit snugly into the MAF loom connector.
    20191106_132423.jpg


    You can also play with different resistors and diodes if you find it still gives you codes. I also tried an LED with an 3k3 resistor and it worked fine as well. But I switched out for the above because it was too bulky with the LED. The key things are: You need a diode to drop the voltage below 5V when in non-EGR mode, and you need a resistor to divide down the voltage when the EGR is active and its 470 ohm resistor is pulling pin 5 down.

    PS. anyone concerned about the job of the MAF on these... don't. Its only there so that the ECU can detect EGR malfunction, this is a requirement of EURO2. The ECU also may or may not have a maximum fuel limit map based on MAF, but that would only normally come into play if the MAF reading was very low, for example a heavily blocked air filter, or blocked CATs. But in that case the MAP/IAT sensor combo will cause the ECU to limit fuel appropriately anyway. One thing is for sure the ECU loves putting the car into limp mode when the MAF sensor fails. This mod prevents that. If you are still worried, know that my 316CDI Sprinter has the same engine and ECU as my ML270, but it comes without EGR from the factory. And hence it doesn't have a MAF sensor from factory either.
     
    Last edited: Nov 19, 2019
    Kev555, MLFaN, gassed up and 2 others like this.
  2. bob 6600

    bob 6600 Senior Member

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    Very interesting post!
     
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  3. Kaurinho

    Kaurinho Member

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    I have an c220 om646 i did egr delete after few tries, gonna try this one day to as my car is running unstable and using too much fuel. It vary a lot from 5-7l/100 km also on Tempomat on 1500 rpm it makes like giving throttle and than loosing power like from itself.. Maybe this helps, or if anyone has another trick?
     
  4. oigle

    oigle Senior Member

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    I guess this would indicate that if your MAF fails and you have already installed the egr delete, then there is no need to replace the crook MAF - just put your shunt in place?
     
  5. OP
    stumo

    stumo Senior Member

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    Yep thats right oigle. Also if you feel a bit down on power, you could rule out a MAF issue by putting this circuit in. Some MAF issues don't result in a code, they just cause fuel clipping by the ECU.

    Basically with this mod, you never have to buy another MAF sensor ever again! Or keep the diode and resistor in your toolkit in case you have a MAF go bad on a long trip when towing your caravan in the middle of nowhere.

    Even if you haven't done the EGR mod, I think all you would need extra is a 470ohm resistor between the MAF signal pin and the EGR PWM low side drive pin at the ECU end. Then you could probably disconnect the EGR connector at the transducer and have EGR deleted. Or plug it in when you want EGR again. You could even do it by running an external wire from MAF pin 5 to the EGR plug, then there is no dicking with the loom at all. The complexity of the EGR delete shunt is due to the MAF, which I have now deleted, so the EGR delete becomes much simpler.

    I don't think this works for OM646, its CDI3 no? In which case it will have a digital MAF sensor. This can only work with an analogue MAF sensor, in the same way as the original EGR shunt mod. So this will definitely work for CDI2, which IIRC is OM611, OM612 and OM613.
     
    Last edited: Nov 26, 2019
    oigle likes this.
  6. oigle

    oigle Senior Member

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    Might just do it before the MAF fails. Good insurance. Thanks Stumo
    Ian.
     
  7. Kaurinho

    Kaurinho Member

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    Thanks for infos... I woun't even try it than.. Even i think it isn't anything digital with that thing, it is just an cable with 5 pins
     
  8. MLFaN

    MLFaN Member

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    Gday mate,

    Great post. Ive been doing my 270 over the last 6 months. If the MAF is deleted would it then be possible to feed more cool air in via a modified air induction system, such as a snorkel etc? I just tried the EGR delete only to have the car go into limp and limit revs to 3000rpm . Replaced MAF after removing shunt. The issue seems to be that i burnt the MAF out by modifying the air induction prior to deleting the MAF. Im not game to try the EGR shunt again without having a spare MAF laying around. I need my car for work so ill try on my next lot of days off then try the MAF delete. Thanks in adavance.
     
  9. MLFaN

    MLFaN Member

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    Gday Oigle

    Just wondering if you are still active regarding the ML270?
    Cheers,
     
  10. OP
    stumo

    stumo Senior Member

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    I have a theory that newer MAFs can't supply the same kind of output current as the older MAFs. Normally this wouldn't be an issue because the ECU does not load the MAF output at all, but the EGR delete mod pulls 20mA from it. My original MAF lasted for 5 years and 70k km under the EGR delete mod before it died. But its "identical" replacement lasted only 6 months.

    If you do the MAF delete it should make the EGR delete simpler, all you would need then is a 470 ohm resistor for the EGR delete. I haven't tried it myself, but in theory it should work as described here...
     
  11. MLFaN

    MLFaN Member

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    I tried both MAF and EGR delete but it seemed to keep going into limp mode. Im confident i done the EGR mod correctly and i followed your instructions to the tee with the MAF delete, but no joy. When i get some time in the next few days i triple check my wire choices for the EGR mod. Ill buy a spare cheap MAF this week and try it all again. Im hoping to get these ones sorted then do the inlet manifold, after which i try get a MAP tune done so i can increase air induction to get more HP .
     
  12. oigle

    oigle Senior Member

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    Yep. Still have the ML270. Probably die with it. With mods done over years, seems almost bulletproof now so may as well keep it.
     
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  13. oigle

    oigle Senior Member

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    Cheap MAFS are usually a disaster unfortunately. With stumo's mod, it becomes irrelevant so maybe you need to persevere with the egr delete and his latest mod. My egr delete has functioned perfectly for 100000km now. Have yet to do stumo's extra mod.
     
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  14. MLFaN

    MLFaN Member

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    Ill keep going. Im in love with the car. Need to find a place in Brisbane i can get an inlet gasket from as i want to do that over my holidays. Ill also have another look at the EGR delete as im keen to keep the manifold clean. Im investigating getting A MAP ECU tune done here in Capalaba so i can delete the MAF and get more air in. Ive done a few other mods including rear bar and tyre carrier
     
  15. OP
    stumo

    stumo Senior Member

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    I wouldn't rush into a tune myself, the trans becomes the weak point and its a prick of a job with no hoist.

    My ml has no EGR, no MAF, no flaps, no cats, and it goes like a rocket. Enough that the ESP kicks in hard on a decent launch on dry tarmac. Everything else is stock.

    Its approaching 310k km now and it still drives really nicely with plenty of grunt. The interior and leather is still really nice, even after suffering raising 3 kids. Id like to think it could easily do 300k more.

    The inlet manifold is a big job to get out and in. I used brass 3/4" BSP pipe endplugs for the flap delete. Oven cleaner works well for cleaning all the crap out when removed from the car.
     
    Last edited: Dec 10, 2019
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  16. oigle

    oigle Senior Member

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    As stumo said - manifold is a bitch to do. Gaskets are O rings and get from MB themselves if you need them. Not too exxy. I reused the old ones. Why don't you spend a few dollars and get a car leccy to do the shunts for you? I did. Nice professional job that way. Cost me about $80 from memory. Big deal.
    As far as mapping goes, I got a mild map done to fix a bad lag off the mark from new. Dangerous at round-a-bouts. The grunt was increased mildly to around 500nm, if you can believe the mapper. Drives very nicely. No EGR, 1 CAT, left flaps in place as no sh1t in manifold now to stuff them up. Will do the maf delete if and when the maf gives up. Installed an extra cooler for the auto as I found it overheated when towing in Oz summers. Full Bilstein damper set made a huge difference to handling, especially when towing. I'll be keeping it for the foreseeable future.
     
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  17. OP
    stumo

    stumo Senior Member

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    Ok I just did this mod on another ML270 today. I tried my theory of a more simple EGR delete first but that was a no-go. It doesn't drive the EGR transducer like I thought it does.

    So I did the normal EGR delete first (https://forums.mercedesclub.org.uk/index.php?threads/disabling-egr.68928/). Then the MAF delete. This ML needed a 8k2 resistor and diode for the MAF delete. It seems to pull more current into the ECU on the MAF pin that mine does. Mine uses a 5k6 resistor. On this ML the voltage needed on the MAF signal line is around 2.2V when EGR is off, and 1.5V when EGR is on. I have yet to measure the voltages on mine - it just worked first time.

    I have no idea why the 2 cars are different. They are both 2002 facelift Oz delivered and only 1 month apart. Mine is April and this one is March. Weird. The good news is the MAF delete has fixed the dangerously slow initial lag this ML had when pulling away. Maybe that issue is related to the difference in current I have seen here who knows. We certainly couldn't fix the issue with a new MAF and there were no codes. It just took forever to pull away from stopped. Mine never had that issue.
     
    Last edited: Dec 13, 2019
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  18. ajlsl600

    ajlsl600 Senior Member

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  19. oigle

    oigle Senior Member

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    I had that issue from new and resorted to a remap to fix it.
     
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  20. MLFaN

    MLFaN Member

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    Just took the inlet manifold out and cleaned it up. Not as dirty or worn as i expected. Will tap and put back together this evening if all goes well. Was a dirty job with a couple of small challenges getting it out but not impossible. Took just over 2 hours and i didnt need to remove fuel rail or anything. Was thinking about removing the heat exchanger. Any ideas guys? 20191216_125133.jpg
     

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