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Thread: Strange Behavior under full throttle

  1. #1
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    Strange Behavior under full throttle

    Hello all,

    Had my audi a3 1.8T 2001 for 2 years now and had it remapped a year ago. Ever since the remap I've had a problem where under full throttle there would be a kind of power on off, on off, up through the revs until i changed gear and then same again. I can hear the induction then DV release then induction again as it happens but obviously under full throttle i dont want any boost loss.
    That's not all, after driving a random amount of time (could be 10mins, could be 2 hours) there would now be a power loss. Not so much limp mode but nothing like the usual power I'd get. The strange thing is if i reset my car (ignition off then on) then I would have power again until it goes off again and then a quick off and on and its fine again.
    But wait there's more. If I'm gunning it, as in joining a motorway ofcourse, through 2nd and 3rd gear I'd have power and the as soon as i change to 4th i lose all power and foot to the floor the car actually slows down like its bogging down or something. Just for say 10 seconds then its back again.

    I have scanned my car using VCDS and i got that 17705 pressure drop error.
    After having this for a year i think it's about time I fixed it so any help would be appreciated.

    Cheers.

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  3. #2
    beachbuggy's Avatar
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    First part sounds very much like over boost, and throttle plate protection kicking in. If the car over boost/surges then the throttle closes to reduce boost, fwhen this happens you get a vacuum and the dv will open. When pressure drops , throttle opens until the next time.

    I would suggest if you've checked All the boost Pipes and other bits then it's going to be a bad remap.
    k1ano likes this.

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    sideways steve's Avatar
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    I'm with beachbuggy on this one, sounds like overboosting to me. Have a good look at the actuator too as it may be that its sticking. Failing all that though it could just be a bad map.

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    Alais DJA's Avatar
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    Quote Originally Posted by sideways steve View Post
    I'm with beachbuggy on this one, sounds like overboosting to me. Have a good look at the actuator too as it may be that its sticking. Failing all that though it could just be a bad map.
    I'm also gonna throw in a new fuel filter, and clean up your injectors.

    Always good to clear the source

    550 cc Injectors / Milltek Exhaust Manifold

    Forge Silicone / Goodridge Hoses / EBC A/R

    G60 SMF / Launch Control Map

    Powerflex Black A/R / H&R Anti-Roll Bars

    Carbon Wrapping / 104Db @5400 RPM

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    Quote Originally Posted by Alais DJA View Post
    I'm also gonna throw in a new fuel filter, and clean up your injectors.

    Always good to clear the source
    May aswell get plugs while your at it.

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    MDG
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    and for the pressure drop fault?

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    sideways steve's Avatar
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    Quote Originally Posted by MDG View Post
    and for the pressure drop fault?
    That would be thrown up because of the overboost issue.

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    Who did ur remap and how long ago? Could u not speak to them about these issues?
    p

    THE BLUE BEAST, TAKEN FROM ME, GONE BUT NOT FORGOTTEN
    RTECH STAGE 2 REMAP NOW RUNNING 223 BHP AND 253 FTLB OF TORQUE,
    SUBARU IMPREZA WRX ESTATE SOON TO BE RUNNING 340 BHP
    ANTI LAG/LAUNCH CONTROL/MAF LESS/ LOVE IT !!

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    Thank you for all the feedback so quickly. The remap was done by a company called Remap Science in bradford. They spent all day on it as they had to plug directly into the ECU. They did say that there was an unlimited warranty on the remap so maybe first port of call is to give them a ring.
    I have next week off, being an aircraft technician in the army I have literally no spare time hence why it's taken so long for me to get round to this. So i will get everything a good clean and check all the hoses next week.

    I'm pretty sure it's a boost issue due to the fact that its such a smooth effect with no juddering or misfiring.
    I take it theres no way to adjust the boost and that disabling the throttle plate protection valve or switch wouldn't be a very good idea.

    Cheers.

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    beachbuggy's Avatar
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    have you checked the pipe that runs to the actuator from the N75 as well? that may have come off and as a result the boost isn't being regulated.

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    Checked the pipes and it is indeed connected both sides. Couldn't see a leak but it was raining and didnt have a torch when i looked.

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    Now it's just a question but you see the air line that goes into the airbox highlighted. Well my car has a cold air cone filter fitted with nowhere to put that pipe so the pipe is just covered with a pair of tights. I'm not sure what this pipe does so I'm curious as to whether this might allow crap into the actuator or any valves??

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    After abit of digging I've discovered that hose is just for the SAI system so no worries there. Am wandering how i can check the actuator for correct operation? Am guessing it's near the turbo. Pictures would be great or a link to one.

    Cheers.

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    I've rang up the remap place who said to give all the boost hoses a good check and if that doesn't pull anything up they will have a good look at it for me. So I've booked it in for a full boost leak and sensor check on wednesday failing that the remap people will work there magic.

    Plus I unplugged the N75 valve this morning and the car runs fine with no boost fluctuations, but with much less power. Seeing as it's still spinning up the turbo and there is still limited boost wouldn't I still feel symptoms if there was a boost leak? Doesn't this point towards a Map problems as the ECU is not restricting boost sufficiently?
    Last edited by andya22; 27th February 2012 at 16:51.

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    Quote Originally Posted by beachbuggy View Post
    First part sounds very much like over boost, and throttle plate protection kicking in. If the car over boost/surges then the throttle closes to reduce boost, fwhen this happens you get a vacuum and the dv will open. When pressure drops , throttle opens until the next time.

    I would suggest if you've checked All the boost Pipes and other bits then it's going to be a bad remap.
    Bingo ...

    I have been searching on the net tonight after a few things came together on a road test tonight - basically the symptoms you describe and those of the OP !

    I bought my car a few weeks ago with a star performance GTRS eliminator turbo, FMIC, milltek and sports cats ... it is re-mapped but detuned from it's original power output. I noticed on the test drive the car felt laggy (or not as responsive as I expected) compared to other turbo cars I have owned. Don't get me wrong the car is quick in the higher revs but not punchy - I put it down to the GTRS turbo taking longer to spool ...

    Anyway I was taken for a ride in an S3 on Saturday which was very much more like what I expected the S3 to be like - this was very quick right off the bat with a stock K04, stock intercoolers and a stage 1 remap. So this made me think my S3 should still be quicker than it is ...

    Tonight driving home I tried various road tests and realised that on part throttle the car feels very much quicker than it is on WOT and seems to reduce power at certain points independanyly of my foot position and I can here the dump-valve dumping on full throttle - I was originally thinking this was compressor surge. Whilsty driving if I turn the ignition off then power is restored until WOT conditions cause the power drop again. I realised something was happening but get no engine codes (using my OBDII scanner) - though Jim at start performance had indicated that boost cut had been removed/adjusted so guess this could be why no overboost code is stored ... By manipulating the throttle position and avoiding WOT then I get very much faster acceleration. I didn't know how to ask the questions and also realised I would probably be told to do some logging etc. which I will do as I gain more experience.

    Anyway this post has made a lot of sense as I was thinking compressor surge, timing being backed off etc. but I hadn't realised the Bosch 7.5 controls the throttle valve and dump valve based on overboost conditions as suggested here. My next course of action was to get stuck into improved diagnostics and measuring boost and re-connecting the N75 as a test. I also have several EBC's from my japanese car tuning days and so may try one of these rather than the forge unos which is currently fitted.

    I will eventually fit the 440 injectors I have and remap the car back to its original power as currently it runs at 265hp maximum but this is clearly not as driveable as it should be.

    Martin
    Last edited by k1ano; 1st May 2012 at 23:20.
    S3 2003 Avus Silver, Sunroof, Chrome Mirrors, Symphony II, Cruise, Heated Seats, Centre Armrest, Ambient Lights, GTRS Turbo, Forge FMIC, Sports Cats, MillTek, Coilovers ...

 

 

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