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Hot!Turbo loosing psi after fast drive

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Matts_SW20
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2019/05/25 22:58:32 (permalink)
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Turbo loosing psi after fast drive

Hi Brains Trust, 
 
Been having this issue for a while. I have a 3S with a CT26 and Electronic Boost Controller and Fuel Cut Defender. 90% of the time it boosts perfectly and responds perfectly. But after I drive it hard and do some hard cornering and boosting the engine drops the psi of the turbo. It's likely pulling timing as the ECU has no control over the turbo as it go's through the EBC. What I want to know is why the hell its doing it. If I turn the car off and wait 5min it's fine so it's likely a sensor somewhere not doing what it should. I'm not getting any CEL lights so no codes to check. If someone can suggest an idea or provide me with a list of sensors I should replace please provide this. Any help is welcome at this point. 

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#1


19 Replies Related Threads

    Matts_SW20
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    Re: Turbo loosing psi after fast drive 2019/05/25 23:08:56 (permalink)
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    Normally with the EBC at no settings the stock boost is 12.5 but when this issue happens it reduces to 7psi and just feels like someones taken over the throttle and lowering it.

    MR2 Club of Australia (NSW Branch) Inc.
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    #2
    Falcon
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    Re: Turbo loosing psi after fast drive 2019/05/26 05:53:02 (permalink)
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    If you are still on the OEM ECU it is probably detecting detonation and doing exactly what it's meant to do and pulling timing to safeguard the engine.
    #3

    Matts_SW20
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    Re: Turbo loosing psi after fast drive 2019/05/26 09:25:27 (permalink)
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    If the knock sensor was picking up detonation then that would cause a CEL light though, wouldn't it?
     

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    Falcon
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    Re: Turbo loosing psi after fast drive 2019/05/26 14:33:03 (permalink)
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    You would expect it would. BUT. Not always.
    Cold dense morning air. A fair old bit of boot into it in third gear and it would no longer boost at all.
    Drove gently just fine. I'm crapping myself. After a couple of minutes it came back as though nothing had happened.
    No CEL at all. Boosts to 15 PSI just fine. Sometimes on the track when I'm giving it what for it will kinda go off song and it will chuck a CEL. No apparent reason but I assume it's detecting detonation. It's a Gen 3 with OEM ECU and a bit better turbo than stock. Hopefully someone with way more experience than me will come in on this topic.
    #5
    Carmikey
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    Re: Turbo loosing psi after fast drive 2019/05/26 17:13:52 (permalink)
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    What condition is your turbo charger in? I've had the same symptoms in a friend car, ended up being a worn seals in his turbo from memory. I'm sure there are other like reasons.

    Sent from my SM-J320ZN using Tapatalk

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    Matts_SW20
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    Re: Turbo loosing psi after fast drive 2019/05/27 20:57:51 (permalink)
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    I've never really had the issue on cold mornings. If anything its when the engine is hot. Could be detonation but I hope it isn't.
     
    I actually hope its the turbo because I have a CT20b ready to go on. The existing CT26 turbo has done 270,000k's so it's probably time for the upgrade. The only thing that bugs me is, wouldn't the problem be consistent if it was turbo related? This is why I think it's a faulty sensor or some electrical gremlin. 

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    feral4mr2
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    Re: Turbo loosing psi after fast drive 2019/05/27 21:21:18 (permalink)
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    i fail to see how even if the ecu has detected detonation and retarded timing that the boost pressure would be dropped, the turbo will still boost to what the ebc is set to.   

    if it's not blown, it sucks
    #8
    Matts_SW20
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    Re: Turbo loosing psi after fast drive 2019/05/27 21:24:29 (permalink)
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    These were my thoughts as well the turbo is not monitored by the ECU anymore. But it gets killed by something in the engine which I assume is it pulling timing given there's little else it could do that would reduce boost pressure. 

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    feral4mr2
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    Re: Turbo loosing psi after fast drive 2019/05/27 21:30:14 (permalink)
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    timing retardation doesn't reduce the amount of boost from the turbo.  

    if it's not blown, it sucks
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    Matts_SW20
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    Re: Turbo loosing psi after fast drive 2019/05/27 21:34:56 (permalink)
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    Something is reducing my available boost and I couldn't think of anything that would be other than timing. I assumed that if its retarding the timing then thats reducing cylinder pressure and the subsequent pressure to spool turbo? Forgive my lack of knowledge I'm no engineer. 

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    feral4mr2
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    Re: Turbo loosing psi after fast drive 2019/05/27 23:17:22 (permalink)
    +1 (1)
    Timing advance/retard alters the point of ignition (spark) in the compression cycle.  It cannot alter the maximum boost at the inlet manifold set by the wastegate.   
     
    Retarded ignition can actually premote earlier spool via higher EGT's, can also provide less/sluggish power, but as above not lower the amount of boost seen at the inlet manifold. 
     
    I'd be more inclined to look at the wastegate operation and ebc.  
     
     

    if it's not blown, it sucks
    #12
    chausta
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    Re: Turbo loosing psi after fast drive 2019/05/28 01:31:42 (permalink)
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    Has the tvsv been disabled?
    #13
    92 Hard Top
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    Re: Turbo loosing psi after fast drive 2019/05/28 12:17:31 (permalink)
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    If its a gen II you have tvis which is controlled by you the ecu, if knock is detected it will close the butterfly and you will have only four intake runners open above 3600rpm. After the car has been switch off and restarted it normally reset back to standard if it does not detected it again. This will affect what you feel. Hard corning low fuel in tank can give a lean out, create knock. Just double check for boost leaks etc.
    #14
    Matts_SW20
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    Re: Turbo loosing psi after fast drive 2019/05/30 18:07:06 (permalink)
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    Thanks for the input all. The Phantom boost leak is still eluding me. I've been hammering the car to work all week and not being able to replicate the fault. Really cold mornings the car will have a cough at peak boost but this is likely my EBC just regulating pressure as it wouldn't normally spool up that fast. 
     
    feral4mr2
    Timing advance/retard alters the point of ignition (spark) in the compression cycle.  It cannot alter the maximum boost at the inlet manifold set by the wastegate.   
    I'd be more inclined to look at the wastegate operation and ebc.  

    Yea I've spoken with Robk about this as well I was misguided thinking pulling timing would result in boost drop. We're convinced its a boost leak that only happens on some occasions but no idea where to start. I think it's time to just bite the bullet and swap in my CT20b
    chausta
    Has the tvsv been disabled?

    Yes, the turbo is not monitored by the ECU anymore it all go's through the EBC and I have a FCD to stop the boost cut.
    grosso
    If its a gen II you have tvis which is controlled by you the ecu, if knock is detected it will close the butterfly and you will have only four intake runners open above 3600rpm. After the car has been switch off and restarted it normally reset back to standard if it does not detected it again. This will affect what you feel. Hard corning low fuel in tank can give a lean out, create knock. Just double check for boost leaks etc.

    I thought TVIS was only a 4A thing. This could be a potential cause. I've ran diagnostics on the car and it hasn't recorded a knock code but it could be that maybe? Such a frustrating issue. 

    MR2 Club of Australia (NSW Branch) Inc.
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