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Overboost but not overboost

Discussion in 'TD5' started by tom1979, Jun 18, 2022.

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  1. sierrafery

    sierrafery Well-Known Member

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    You are right but it happens as i said in post #14, i've seen false driver demand fault codes triggered by low fuel pressure(only on Eu3 engines) and as that code is TPS related the EML can come on as well, not very common but it happens, as about the pump IMO this particular part is not compulsory to be genuine even though it's a lottery, they will deliver the fuel regardess of brand eventually not last so long or be noisy but there are good pumps at 1/3 of a genuine's price like Stark for example
     
  2. tom1979

    tom1979 Well-Known Member

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    So, there was a driver demand fault “Problems detected with driver demand (logged)”.

    just once with the ignition on and engine off I made the same fault come back by pressing the throttle fully down, I cannot make it do it again
     
  3. sierrafery

    sierrafery Well-Known Member

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    Then it can be the TPS itself too but i'm inclined to suspect a fuel pressure issue as when you push the throttle down the pressure doesnt reach the necessary limit to bring up the revs as expected at that throttle position and usually the TPS issues are not so intermittent and not only under load... try this as first step: Check Td5 fuel pump HP
     
    Last edited: Jun 23, 2022 at 9:30 AM
    tom1979 likes this.
  4. Discodevon

    Discodevon Well-Known Member

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    I had that fault code logged when I had a non genuine turbo arm on my turbo, changed it to a genuine part and it went along with the splutters
     
  5. tom1979

    tom1979 Well-Known Member

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    Should the mV be constant at all revs or just at idle?
     
  6. sierrafery

    sierrafery Well-Known Member

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    It should be around the idle value at all revs but it might fluctuate a bit, if it drops hard under rpm the pump is gone
     
  7. tom1979

    tom1979 Well-Known Member

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    At idle it flickers between 20-24mV. I’ll get someone to rev it shortly
     
  8. sierrafery

    sierrafery Well-Known Member

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    Seems that the pump is OK then
     
  9. sierrafery

    sierrafery Well-Known Member

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    Is your ECU remapped?
     
  10. tom1979

    tom1979 Well-Known Member

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    Yes it is.
     
  11. sierrafery

    sierrafery Well-Known Member

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    Then try again with MAF unplugged and if the symptom doesnt occur that way regardless of load we'll speak then
     
  12. tom1979

    tom1979 Well-Known Member

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    At the weekend I tried with the MAF unplugged and had no issues so assumed (maybe wrongly) the MAF was at fault
     
  13. sierrafery

    sierrafery Well-Known Member

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    If with MAF unplugged there are no issues at all BUT with a genuine MAF does the same then the problem is with the turbo or a slight boost leak somewhere as the air flow exceeds the cut-out limit while the boost is below expected at a high driver demand then the fuelling is increased as to reach the boost target which creates higher than normal sucction = too high air flow reading. It's quite common such symptom to occur on remapped Eu3 engines if the air flow limit was not raised in the fuel map...that's why the EGT is a bit higher than normal on your's
     
    Last edited: Jun 23, 2022 at 3:36 PM
  14. Discodevon

    Discodevon Well-Known Member

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    A few tuners offer a maf delete in the remapping,what do you feel about this? Obviously a new genuine maf sensor is near £200 pounds now
     
  15. sierrafery

    sierrafery Well-Known Member

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    I didnt feel well about this at the beginning but i changed my mind cos I have friends with Eu3 engine who did it and IMO if the tuner guy knows his stuff it's the best option cos you dont have to worry about MAF anymore while the engine can run very well based on MAP/rpm fuelling addapted for green top injectors and only the genuine MAF is 100% reliable also it's possible that your problem is with the turbo, wastegate or a slight boost leak which occurs only under heavy load so not even a genuine MAF would work with that. At the price of genuine MAF's i'd go for a remap if i was you, and if you do it tell them if you have bigger tyres cos the fuel map can be addapted to that too
     
  16. tom1979

    tom1979 Well-Known Member

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    I always recommend keeping the MAF, even on the EU2 engines I think they run better. But Sierrafery is also right in that if they are mapped out properly there should be no issues
     
    Last edited: Jun 23, 2022 at 6:43 PM
  17. tom1979

    tom1979 Well-Known Member

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    so I unplugged the MAF again today , and no problems.

    assuming there are no problems over the next few days what could have suddenly starting making the MAF have issues?

    I’m confident there are no boost leaks, the whole intake and exhaust systems have been smoke tested under pressure.
     
  18. sierrafery

    sierrafery Well-Known Member

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    The MAF has no issues the problem is the increased air flow so if you are 100% certain there's no leak...which can be through the wastegate port too then it's possible that the turbo cartridge is worn and it must turn harder to deliver boost which means more sucction too... once your's is remapped anyway better get a proper remap with deleted MAF than change several sensors cos the incresed sucction is killing them as well
     
  19. tom1979

    tom1979 Well-Known Member

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    the vehicle was remapped in January 2020 by a well known tuner who’s been doing it for 20ish years, but the problem only began a few weeks ago. It is possible the turbo could be worn but I have not noticed air flow readings that might exceed the MAF limit which I think is around 680kg/hr or thereabouts.
     
  20. sierrafery

    sierrafery Well-Known Member

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    You can rarely observe those readings in instrument mode, save an inputs fueling log with MAF connected then we'll see if that's the case or not but the fact that the vehicle behaves well with MAF unplugged is enough evidence for me that the problem is with the air flow ...unless you want to spend big money for a genuine MAF to see how it goes then or just to end up the same
     
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