No Injector Quantity Deviation for Cylinder 4

Discussion in 'VW Mk3 Jetta, Passat TDI and other/older diesels' started by Chris George, Mar 7, 2017.

  1. Chris George

    Chris George New Member

    Joined:
    Oct 31, 2016
    Messages:
    5
    Car:
    15 Audi Q7 TDI; 98 VW Jetta TDI
    Location:
    Bremerton, WA
    Should AHUs (98 Jetta TDI) show Injector Quantity Deviation for all 4 cylinders under Grp 13 in VCDS . . . or is it a comparison between cylinder for just the first three values?

    Mine shows:
    1 0.46
    2 -0.19
    3 0.42
    4 blank

    Is this normal (please say yes) or does this mean the ECU doesn't see cylinder 4 firing or something else?

    No Codes (except Radio Amplifier intermittent ground).
    Timing Good (very slightly advanced)
    IQ is ~4.5 at idle once warm.

    I have been troubleshooting poor gas mileage and low torque at low RPMs:
    -Found that a rat made a next under the window cowl and chewed through the MAP hose . . . cleaned up the mess, checked the wires (look good), replaced the hose, and check for leaks . . . .still poor mileage (25-30 vice 40-49) and low RPM torque.
    -Started VCDS troubleshooting and saw that the Engine Coolant Temp was not getting above 36C . . . checked resistance on the ECT sensor, saw it was bad, and replaced it. Now slowly gets up to 70s at idle and low 80s after a long drive, but still poor mileage and low torque.

    I am worried based on the above that cyl 4 is not firing and am planning to check injectors and compression. Will do these regardless of what the answer to the above is, but it could help me think in the right direction if I knew what to expect. I pulled the rocker cover this afternoon . . . didn't see any irregularities with cam or lifters (at least from the topside). Appreciate an answer to the injector deviation question and any other recommendations.

    -Chris
     
  2. audi1z

    audi1z Member

    Joined:
    Oct 16, 2010
    Messages:
    406
    Car:
    Audi 80 1Z Engine
    The values are references to cylinder #3 which is the one with the needle lift sensor.
    The IQ deviations look very good, similarly the IQ.
    Group 13 has to be read as follows:
    1 - deviation cyl 4 to cyl 3;
    2 - deviation cyl 2 to cyl 3;
    3 - deviation cyl 1 to cyl 3;
    4 - blank, because in this measurement logic meaningless;

    The slow warming might indicate problems with your thermostat. But that should not be the reason for poor torque.
    I would check the MAF values and particularly the boost pressure.
     
  3. Chris George

    Chris George New Member

    Joined:
    Oct 31, 2016
    Messages:
    5
    Car:
    15 Audi Q7 TDI; 98 VW Jetta TDI
    Location:
    Bremerton, WA
    Thanks, good to hear that it is not likely a deep mechanical problem. I was going to go down the path of a thermostat problem until I saw the deviation numbers . . . thanks for setting me straight. I just wish the thermostat was in a more convenient spot . . . I'll check MAF and boost numbers before I drain the coolant again (changed about 15K ago). I will test the compression . . . since I finally splurged on a 'relatively' cheap test kit.
     
  4. audi1z

    audi1z Member

    Joined:
    Oct 16, 2010
    Messages:
    406
    Car:
    Audi 80 1Z Engine
    The cylinders a such equal that all of them would have a comparable low compression. Consider that. Regarding the "cheap test kit", kepp in mind that you must not expect to measure values comparbale to those of the factory.
    Cheers
     
  5. Chris George

    Chris George New Member

    Joined:
    Oct 31, 2016
    Messages:
    5
    Car:
    15 Audi Q7 TDI; 98 VW Jetta TDI
    Location:
    Bremerton, WA
    Providing an update for anyone who happens to look for resolution on similar problem: The MAF and MAP look good on datalog (MAF reads higher than specified due to mods, but consistently). 20 minutes of highway driving to reach 80C this morning with more than half the radiator covered and outside temp of 2C. By the logs it looks like not only is my relatively new thermostat stuck open, but the coolant glow plugs are having no effect either (I do not think they have ever been changed). I will update after I have swapped the thermostat (again) and troubleshot the coolant glow plugs.
     
  6. audi1z

    audi1z Member

    Joined:
    Oct 16, 2010
    Messages:
    406
    Car:
    Audi 80 1Z Engine
    Remind that the coolant glow plugs are switched on only at temperatures below about 5 °C (coolant and intake). There are two relay switched circuits, controlled from the ECU. You can check the switching separately with VCDS (output tests), or monitor in group 16.
    The readings (VCDS) of the related temperature sensors are ok (VCDS, group 7) ?
    Cheers
     

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