RPM keeps climbing with no throttle?

Discussion in 'Forced Induction - 5.0L V8 Engine' started by ForYourOwnGood, Jun 26, 2019.

  1. OP
    OP
    ForYourOwnGood

    ForYourOwnGood Well-Known Member

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    No I was careful not to move it at all. I know better than to damage those diaphragms.

    OEM throttle body, yes catch can and no long tubes. I have a tune revision that disables the rev hang I just haven't had a chance to get it flashed yet. This effect only happens some of the time so its really hard to pin down. I have checked for vacuum leaks and had it smoked, my buddy has one of the smoke generators and plug kits. I'm also not getting any symptoms of unmetered air in the system at all.
     
  2. aleccesarenriquez

    aleccesarenriquez Well-Known Member

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    DId you ever figure out the issue? I'm having this exact same issue right now. Log looks identical

    upload_2020-5-25_3-6-57.png
     
  3. aleccolin

    aleccolin Well-Known Member

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    Can you log throttle plate position also?
     
  4. aleccesarenriquez

    aleccesarenriquez Well-Known Member

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    Do you know what that pid might be called? Don't really see any mention of a throttle plate position in the ones I have listed.
     
  5. aleccolin

    aleccolin Well-Known Member

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    No, but I think they're called Throttle Angle and Throttle Angle Desired (?)
     
  6. aleccesarenriquez

    aleccesarenriquez Well-Known Member

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    Doesn't look like Lund included those pids in their config file. Be interesting to see if the throttle body is actually getting stuck open like that.
     
  7. Burkey

    Burkey Well-Known Member

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    Here’s one of my logs from a Lund tune. Note the selected PIDS (rpm, pedal and throttle blade).
    Here’s the thing:
    I distinctly remember this particular log and how I had to pedal it a bit at the top of third gear.
    You can see me dancing on the throttle to straighten the car up, but according to the log, the throttle blade remained wide open (it absolutely did NOT remain wide open).
    I can’t explain what’s going on here. 120900D5-49FC-4FFD-8469-21FA91AD5EBD.png
     
  8. Avispa

    Avispa Well-Known Member

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    Faulty throttle position sensor maybe. Its the only way the PCM knows where the throttle really is. An intermittent sensor might not throw an error code.

    You'd think after 15 years with electric throttles thus kind of stuff wouldn't happen but....
     
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  9. aleccesarenriquez

    aleccesarenriquez Well-Known Member

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    Didn't know ETC_ACT was throttle angle. Here is that same log. Looks like throttle closes a little bit after I left off but for some reason rpm spikes to over 8100 anyways. Throttle angle seems to decrease too so it's not getting stuck open either.

    Looking at your log shows an even more substantial throttle delay. Have you tried to resolve that or have you just made it an afterthought? I did notice your rpms fell accordingly when you did let off. Mine just sky-rocketed.

    Lund did get back to me and said the behavior was normal. Not entirely convinced yet.

    upload_2020-5-27_2-13-20.png
     
  10. Burkey

    Burkey Well-Known Member

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    That’s the weird part, there is NO delay in reality. Not sure why the log shows what it shows. I clearly remember having to get off/on the juice to straighten it up, along with the car doing as a I’ve asked (as you can see with the rpm change).
    If you look at it carefully, you can see where the wheel spin started, my reaction on the pedal, rpm dropping cos it hooked again, me having another gentle stab at it and then giving up.
    I’ve highlighted (in red) the bit where I’d say I’ve “called it” and the bit where the ETC_ACT decides to drop off. The time difference between those event is 0.12 seconds.
    The interesting part to me is that the ETC_ACT doesn’t move at all until the pedal is at 3%.
    I can’t explain any of it. The car drives just fine, no hang, nothing of the sort.
    It’s as though the PID isn’t grabbing the data correctly for whatever reason. BA264072-26AA-488D-865C-F75E602CBF6D.jpeg
     
  11. aleccesarenriquez

    aleccesarenriquez Well-Known Member

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    Might be due to a slower sampling rate from the throttle sensor?

    My issue is a little bit different though. Your rpm seems to respond fine to letting off, while mine wants to go to the moon.
     
  12. aleccolin

    aleccolin Well-Known Member

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    How are your BOVs plumbed? Are they venting to atmosphere? Where is the boost/vac reference coming from? You don't have a check valve in the boost reference line, do you?
     
  13. Burkey

    Burkey Well-Known Member

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    I think you’re dead-on. Even when the pedal goes WOT at the start, you can clearly see the lag in response of the etc PID. Seems that it’s not the most reliable source of data.
     
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  14. aleccesarenriquez

    aleccesarenriquez Well-Known Member

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    They are routed off the vacuum block, along with everything else. No check valves
     
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