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MAF issue

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by bhonok, Dec 3, 2012.

  1. bhonok

    bhonok Senior Member

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    Your Mercedes:
    ML 270 CDI 2001, OM612
    2001, ML 270 CDI. Recently purchased. Trying to sort out many problems. Car runs, but blow black smoke and no power uphill. MAF is not getting 12 volt supply from Red/blue wire post 4 in connector. when test 2 and 3 show 5 volts, but 3 & 4 show none. traced this wire all the way to ECU. Solid wire ... Tried to run hot wire from battery, but getting alarming constant beeps possible from throttle module...So maybe MAF is dead but first need to power it to test..Any help is appreciated...
    I have cleaned inlet manifold and all seems OK But need to know how much lateral movement should the actuator of motor produce.. Mine only open flaps fractionally some 20%.
    Next project is vacuum system and turbo( dripping oil)
    Many thanks.
     
  2. television

    television Always remembered RIP

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    Your Mercedes:
    2002 SL500, 216 CL500, all fully loaded
    5 volts is the max used in this system, so that is Ok , it is not expensive for your engine, do not buy from Ebay
     
  3. mej

    mej Senior Member

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    Your Mercedes:
    S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
    Since you already suspect the inlet port shut off motor/flaps, why not try this cheap option first? Courtesy of Alex Crow, Dman and others.

    Inlet port shut off motor delete (CDI2)
    ________________________________________
    A popular mod now, is to disable the inlet port shut off flaps, particularly on 270 CDI (612) engines.
    This is usually done because of damage to the flaps from wear and tear, accelerated by EGR gasses.

    It is possible to replace the entire manifold, but at significant cost, and some of these cars are old and unloved now!
    Even if the manifold is changed, problems can still occur with the actuator motors (M55) jamming and signaling faults to the ECU.
    So, how to do without the system...

    To remove the flaps is simple, but leaves big holes in the intake manifold.
    To plug these holes, I cut short sections of 16mm threaded bar, tap threads in the holes, fit the plugs with superglue, and finally drill and lockwire them for good luck.

    With me so far?

    But we still have a problem, if the motor is removed, a fault code will be logged, stating 'M55 inlet port shutoff motor signal wire resistance too high'.
    Yes, the motor can be left in place and connected to the loom, and if working there will be no fault code.
    However, as is often the case, the motor may have heavily worn gears, and frequently jam.
    This will log a different code - 'M55 inlet port shutoff motor signals fault through ground keying', which simply means the integrated circuitry in the motor has seen that its mechanism is jamming, and has signalled a fault to the ECU by temporarily grounding out the signal wire.

    So, if the motor is worn and jamming, we have a problem, but we do not want to replace it with a new one, especially now there are no flaps fitted.

    Getting there now...

    So, to cut to the chase, all we need to do to avoid logging fault codes, is wire in a resistor between the signal (PWM) wire and the 12v wire to the M55 motor.I have found that values from 1k to 10k ohms work - 20k ohms is too high.
    I have opted for 4.7k ohms on my testbed, and so far all is well - no codes being logged.

    I should add that you can buy these mods on ebay http://www.ebay.co.uk/itm/Inlet-port...item1e6a7d237e , but they are rather more expensive than a 4.7k ohm resistor...
     
  4. OP
    bhonok

    bhonok Senior Member

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    Your Mercedes:
    ML 270 CDI 2001, OM612
    Thanks for response. 5 volts is OK, but I am not getting 12 volts to MAF. This red/blue wire that runs from ECU to MAF is solid but carries no voltage... I don't know if my MAF is OK until I power it up. Now car runs the same with MAF disconnected...I would appreciate if somebody with same vehicle can disconnect MAF connector and measure voltage between socket 2 and 4. If there is 12 volts there with ignition on it means something wrong with my ECU.
    Thanks
    My mistake ... the voltage should be checked between socket 2 and 3, not between 2 and 4.
    Thanks
     
    Last edited: Dec 6, 2012
  5. television

    television Always remembered RIP

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    There is no 12 volt going to the MAF as far as I know, just the standard 5 volt logic voltage. If it is the same unplugged then it could well be faulty.

    I had all the data on these but its gone when my computer crashed, I will be getting some data back soon.
     
  6. OP
    bhonok

    bhonok Senior Member

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    Thank you MEJ for excellent input. Before I go for this big job I need to be sure my motor or actuator are faulty . I suspect, but you know " innocent until proven guilty" Motor seems OK and manifold and flaps are cleaned. Now I need to know how much movement of the actuator should there be for system to function well.? As I said mine only opens flaps some 20% Is it enough or it should be complete opening.
     
    Last edited: Dec 6, 2012
  7. OP
    bhonok

    bhonok Senior Member

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    I checked MAF connector and out of 5 only 4 wires are there. Red/blue, Brown/tan, Brown /yellow and Yellow/white. the Yellow/green socket is empty. With key in position 2 the voltage between #3 B/T and# 4 B/Y is 5 volts which is correct, however according to electrical diagram there should be 12 volts between # 2 R/B and # 3 B/T. and I do not have it even with motor running????
    Maybe your system is different...
     
  8. mej

    mej Senior Member

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    Your Mercedes:
    S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
    Can't give you a figure (say in degrees) for the motor movement, bit it's quite noticeable as you peer down through the manifold from above.

    I attach a diagram of my (OM646.961) MAF wiring, but may be of little help. I think you're saying your plug has 5 pin slots, so I'm sure deffo should have the 5 wires.

    When I did the flaps on mine (150k mi) and a W210 320Cdi (200k mi) they were very bunged up and totally disgustong repectively, so prob worth a revisit. I can't check the voltages on mine just now to confirm there's no 12v to power the sensor, but as Malcolm says the signal transfer runs on 5v.
     

    Attached Files:

    • MAF.pdf
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  9. mej

    mej Senior Member

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    Your Mercedes:
    S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
    Sorry - forgot to mention; the MAF is B2/5
     
  10. television

    television Always remembered RIP

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    That is correct
    Plus 5 volt
    Ground
    Reference
    Output
     
  11. OP
    bhonok

    bhonok Senior Member

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    Hi Malcolm. As you see from file attached there should be a voltage between sockets 2 and 3, plus reference voltage 5 between 3 and 4. Yet this diagram from gasoline vehicle. I need somebody with ML 270 CDI to help me with this dilemma
     

    Attached Files:

  12. television

    television Always remembered RIP

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    My computer is brand new and I cannot open that yet :(
     
  13. mej

    mej Senior Member

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    Your Mercedes:
    S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
    Is yours a ENGINE 612 in MODEL 163.113 up to 31.8.01?
     
  14. television

    television Always remembered RIP

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    No it will be a diesel starting with a 61 and one more
     
  15. mej

    mej Senior Member

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    Your Mercedes:
    S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
    The 612 is a diesel isn't ? I have from the WIS Document number: pe07.16-p-2000-99gh, Document title: Wiring diagram of common rail diesel injection (CDI) control module a schematic which shows the MAF B2/5 as having pin 3 Bu GND, pin 5 Y/W SIG, pin4 +5v Bu/Y, pin 2 12v R/Bu. No pin 1 shown.

    Hope this is of some use.
     
  16. OP
    bhonok

    bhonok Senior Member

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    Your Mercedes:
    ML 270 CDI 2001, OM612
    My engine is diesel, 612963. Model 163 113. The schematic and wiring that mej is referring to is correct. MAF connector has 5 sockets but only 4 wires . Position 1 is not occupied. And wire R/BL at socket 2 should deliver 12 volt... This wire in my car runs from ECU (connector 4 pin 11)to MAF. So it looks like ECU is not supplying...unless I am missing something???
     
    Last edited: Dec 8, 2012
  17. mej

    mej Senior Member

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    Glad we sorted that out!

    Broken wire? Previous owner clumsy intervention? If you have no 12v feed, would suggest a temporary direct, switched, 12v shunt to the MAF to see if this improves matters. Also strongly recommend the insertion of the resistor in the M55 swirl flap motor plug and disconnecting it as described earlier. Possibly as 2 separate operations to assess the effect of each independently.
     
  18. OP
    bhonok

    bhonok Senior Member

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    Your Mercedes:
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    Thank you MEJ. The Red/Blue wire is solid all the way and there are no traces of tempering in ECU box. I have already tried to run a hot wire straight from battery to MAF socket 2. Unfortunately I am getting very alarming beeping sounds like some system goes for self test that wouldn't stop and I am afraid to burn ECU or throttle control module. Maybe I am not taking into consideration the amperage issue... I have trouble identifying the source and a reason for this non stop buzz. My vehicle is very challenging...
    About flaps I am with you. Try to explain how it would affect performance and especially consumption. After all they were designed by engineers for some reason and arguing with engineers is not one of my strong points...
    Thanks again. Boris
     
    Last edited: Dec 8, 2012
  19. mej

    mej Senior Member

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    Your Mercedes:
    S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
    I can think of no further action to suggest on your ML. I regret to agree the ECU does look to be a possibility. As to the swirl flaps, my experience is limited to my OM 646 220cdi and my d-in-law's OM613 320cdi. In both cases the flaps were very gunged up and I removed them as others have done. A search for threads on MB sites is your best bet. Here's one - http://www.mbclub.co.uk/forums/engi...di-inlet-manifold-flaps-remowal-pictures.html.
    Both the family cars run well without the flaps, possibly with improved consumption. The general opinion is that the flaps may help combustion and emissions when the car is new, but at 100+k miles and mucky they restrict the inlet flow severely. Then there's the possibility of the motor failure (I had it on an earlier 320 cdi of mine) where the cost of replacement is significant for no tangible benefit, and possibly worse consumption.

    I hope you find your way through the problem.
     
  20. mej

    mej Senior Member

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    Except I did suggest a switched 12v feed to the RBu pin. Perhaps if the ECU sees there is already a supply on start up it doesn't like it?

    Bon courage
     

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