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low boost and have checked everything i think?

Discussion in 'A4/S4 forum(B5 Chassis)' started by BigBen, Mar 16, 2010.

  1. BigBen
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    BigBen Member

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    [Mar 16, 2010]
    Hi, my 1.8t was having erratic boost issues since i got it- sometimes it would pin you to the seat and other times it felt flat as.

    The car came to me with superchip eprom fitted (documented and stamped ecu cover)

    In a bid to cure this i have changed dv to forge splitter, n75 to the J version, boost hoses all replaced, TIP replaced with silicone, but still the problem continues. Changed FPR vacum hose, changed vavum hose from DV to inlet.

    On the vdo boost gauge it under load will bosst to 0,5 bar maximum then drop back instantly

    When i rev it and jump off throttle the revs hunt low for maybe 5 seconds then stabilize at 850rpm as expected. Read as much as possible and can't work it out- have swapped the maf to another one and that was same?? HELP!
    :readit:
    Last edited: Mar 16, 2010
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  3. B5NUT
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    B5NUT Well-Known Member VCDS Map User

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    [Mar 16, 2010]
    Throttle body calibration? (For the low revs)
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  4. BigBen
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    BigBen Member

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    [Mar 16, 2010]
    Yeah have disconnected the battery and short the positive and neg then reconnect, this realigns the throttle body like vag com..?
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  5. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 16, 2010]
    A standard AEB should boost to 8psi or 0.5-0.6Bar. Chipped i'd expect 14-15psi or 1bar. It should hold that boost to around 5krpm at least.

    Are there any fault codes?

    The N75 J valves are known to cause problems, the boost spikes too quickly, and the ECU goes into limp mode
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  6. BigBen
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    BigBen Member

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    [Mar 16, 2010]
    Hi mate,no faults.I fitted the J version to see if the fault lay with old N75- i could try and swap them back. Anybody had any problesms with vacuum pipes around the servo- only asking as i seen a video on you tube about boost leak on b6 and i had big one off inlet mani to servo??

    It's burstin my tights this is as is the idle :motz:

    Thanks for replies thus far folks
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  7. BigBen
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    BigBen Member

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    [Mar 16, 2010]
    Could this be the wastgate sticking open? :crying: What would the symptom of that be- could i repair it without removing the turbo
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 17, 2010]
    thing is, if its electronic, it should log a code, and if it was mechanical it would log a code.... When our wastegate broke there was a fault code saying it couldnt generate any boost.

    Perhaps a MAF fault? That could give wonky readings and not pop a code i guess. if your near me i've got a spare you could test with...
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  9. BigBen
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    BigBen Member

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    [Mar 17, 2010]
    Thanks but I'm in Edinburgh. I have cleaned the maf with maf cleaner, made no difference. It's bursting my head it is.....:motz:
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  10. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 17, 2010]
    Hmm...

    I'll be in edinburgh in a few weeks, so i guess we could try it then?

    Unplug the MAF and see if the car drives better. If it does, its almost certainly the culprit.
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  11. BigBen
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    BigBen Member

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    [Mar 17, 2010]
    Well that would be interesting to try..... do you beleive that could cause the boost loss? Sometimes it flys but others it's poo..............
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  12. BigBen
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    BigBen Member

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    [Mar 17, 2010]
    What symptom would a stuck open wastegate give me? I am leaning towards this as it trys to build boost but just drops back down..... Can the wastegate be repaired or replaced?

    Also quickie question what FPR is fitted to our cars 3 or 4 bar?

    Thanks guys
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  13. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 17, 2010]
    If the wastegate was stuck open you'd get no boost at all.

    I guess if the actuator was weak, it might do what you describe, but then the ECU would notice it cant make any boost, and flag up a fault code.

    Have you tried unplugging the Airflow Meter yet?

    4Bar FPR on an AEB
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  14. BigBen
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    BigBen Member

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    [Mar 17, 2010]
    Will try unplugging the MAF tomorrow and see if any different. Also want to check the vacum hose the goes to the servo to make sure it's sound.

    I will report back.....:bye:
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  15. BigBen
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    BigBen Member

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    [Mar 18, 2010]
    So this morning changed back to N75 c and it is bit better,it is spiking at about 0.7 0.8 bar which i think is only 12psi............. that's not right???

    I done pressure test on syste and allowed it to build to 1.5bar and it held with no leaks or problems.

    I have been in touch with forge regarding the splitter valve i have fitted and am disappointed they are not helping me??? WTF I have the valve now dialed all the way to the right making the spring as tight as possible? It leaks air from the 'trumpet' all through the revs then when you lift off it blows off as it should.

    Also had a fault code for engine temp sensor today but cleared it and and inspected the connector put it back on ran it for 20mins and no code re-appeared? I did buy a new green temp sensor when i got the car but it had much slimmer pins and different shape to current one- obviously for different 1.8T engine. If that sensor is at fault intermittently could that cause low boost?

    The way i feel about forge after sales at the moment is not worth writting but hopefully they will get back to me today to clarify if the valve should be bleeding air all the time?? I will advise what they say..


    :no:bloody splitter
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  16. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Mar 18, 2010]
    If you are not chipped that value is correct 12 PSI is around what a TQS should be giving you. Mine does the temp sender code now and again, and i have a new sender in there and the wiring checks out as best as i can tell. The next step will be replacing it from the sender plug direct to the ECU for me,so for now will probabbly leave it as is,lol
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  17. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 18, 2010]
    This is why its completely pointless fitting barry valves. Just fit a nice standard 710N. You've got far too many variables going on, and a leaking dump valve isnt helping anything. Its certainly not supposed to be leaking.

    Sensor wouldnt cause low boost, just potentially bad running. A faulty thermostat can also cause a CTS fault code, i had it pop up a few times with the faulty stat.

    Mark: its not a TQS i dont think, but it probably is the remap only making 12psi. I've heard a few times that superchip maps only make around 185hp.
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  18. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Mar 18, 2010]
    Ahh my bad, in which case it could be right, my old Chimped Uk map ran around 12 PSI averagly. Sometimes spoked more under massive load or in warmer weather etc As everyone is aware the cooler weather tends to lend itself to lower boost due to less pressure needed due to the air being denser ( like me DOH!)
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  19. ado66
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    ado66 New Member

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    [Mar 26, 2010]

    don't think so
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