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Thread: Boosting problem on z20let

  
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    Darren_mk4's Avatar
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    Boosting problem on z20let

    I bought a mk4 gsi a few days ago but previous drove a c20let mk3 and dont think the mk4 is boosting all that great.

    its standard bar a cat-back, silly induction kit and dump valve.. there is also a homemade catch tank fitted?

    When boosting through the gears it starts to boost, then feels like its holding back but picks back up.

    What psi should they run standard?

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    pete-gsi's Avatar
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    in 5th mine over boosts to 10psi but holds at 8psi

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    1-2 gear max 0.5 bar, other gear boost 0.6-0.7 bar..overboost under 0.9 bar
    Astra Coupe Turbo / LPG conversion

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    Could be actuator mate I have this...
    FORMERLY WAVEYBLUEWATER

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    Darren_mk4's Avatar
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    Its due on the rollers on the 1st of november.. last night (on private roads!) it boosts through 1-3rd... but 4th and 5th seem to be dead, turbo is spinning but doesnt really pick up any speed??

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    Can't see why it'd be "gear specific" if you know what I mean, if it's not going to boost properly at say 3500 rpm then it'd do it in every gear??

    Do you have a boost gauge on it as you'd see then if the boost is dropping off then picking up again?
    FORMERLY WAVEYBLUEWATER

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    Quote Originally Posted by Waveybluewater View Post
    Can't see why it'd be "gear specific" if you know what I mean, if it's not going to boost properly at say 3500 rpm then it'd do it in every gear??
    Isn't the boost restricted in the lower gears on a standard ZLet?

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    Actually yeah it is isn't it but I'm sure that it's only 1st and 2nd though??

    But that'd mean that you boost better when it's restricted lol, some strange sh** going on there lol..

    No idea personally, could be any any the following that's being affected on higher boost?

    Boost Control Solenoid.

    Actuator struggling to keep the wastegate shut under all the exhaust gas pressure. (same as mine's doing - boosts, drop alot then equals out and boosts up a bit again)

    Dump valve leaking under high pressure as you have an aftermarket one on don't you?? (Is it a Bailey DV-26 / 36??)

    I don't know what else to suggest split vacuum hose??
    FORMERLY WAVEYBLUEWATER

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    boost is restricted via the ecu and speed related,this is done so it dont kill the gearbox,i'm thinking it dump valve relatated and would bet that the person b4 has taken the vacum pipe off the rear boost solenoid and put that up to the dump valve and blanked the re cerc valve on the turbo,if ya can m8 have look and follow the small vacum pipe off the dump valve and see where it tees into it should go behind the cross over pipe on top of the engine and onto the fuel pressure reg valve but i reckon yours goes either down the back of the engine or accross to the pipe tht should go onto the turbo by the air con pump
    courtney stage 3 zafira,Mitsubishi evo geek mapped to 389 and 470 lb of torque

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    Darren_mk4's Avatar
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    sorry to bump this thread but am told my turbo its ****ed.

    it was replaced by vauxhall in 2006 but now when left on idle for 10 seconds say and i move off it smokes... vxr turbo time?

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