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  1. #1
    AL_B's Avatar
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    Hesitation and Can I believe this Rolling Road Figure?

    Hi everyone,

    As most people know my car has had an intermittent hesitation problem for over 2 years, and I've still not got to the bottom of it. [img]/ubbthreads/images/graemlins/bang.gif[/img]

    Anyway, a couple of weeks ago I felt I should throw a bit of money at it, and booked it in with Awesome GTi just round the corner.

    They (Andy and Jim) were very friendly and very helpful. I gave them lots of info on what I have already tried etc. Which they appreciated.

    Their investigation was not fully conclusive, but it was highly likely that it was the MAF sensor. They said it had thrown an error code, but unfortunately the mechanic had not saved the code before clearing it.

    Anyway, I asked them to try out a new MAF and see if the car was any better. I also asked Jim to put it on their rollers.

    Jim compared a brand new MAF and the alledged "faulty" one on my car. During the rolling road testing (12 runs in all), both MAF's performed fine. And no hesitation occurred.

    I kept the "faulty" MAF fitted as I intended to get it replaced under warranty yesterday at the dealers. Which they didn't because no errors were reported.

    Anyway.....the result of the rolling road at Awesome-GTi (DynoJet WinPep 7) was:

    195.63 bhp and 201.01 lbft @ wheels

    Run conditions: 77.8 degF, 30.24 in-Hg, Humidity: 35% DIN: 1.00

    Jim and Andy said add approx 40 to the bhp figure to get the figure at the flywheel. Apparently the software/rolling road struggles with Haldex in trying to work out the rolling resistance to get the flywheel figure.

    What do you think?

    I know this is a very different rolling road to others out there. So is 40 about right to add?

    AL

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  3. #2
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Alan, you can really only add the figures from the RR that relate to losses. If they didn't measure drag output then you can't reliably add anything to the known wheel figures.

    The wheel figures look high for a standard car and in my experiences drag losses are usually in the region of 60-80bhp. It depends how the car was run - full 4wd, partial 4wd or 2wd also.

    Also, torque is torque and generally no differentialtion is made between wheel torque and flywheel torque- the RR torque figure is THE torque figure and in which case it's low - as reflected by your own VAGCOM runs and previous dyno runs.

    Did they log boost? Did they / can they log req throttle with actual throttle position? All useful - a faulty TB will give hesitation and low power potentially... What about logging misfires, fuelling, mixture etc....

    I'm still stumped for a more definitive solution though [img]/ubbthreads/images/graemlins/frown.gif[/img]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    Alan, you can really only add the figures from the RR that relate to losses. If they didn't measure drag output then you can't reliably add anything to the known wheel figures.

    The wheel figures look high for a standard car and in my experiences drag losses are usually in the region of 60-80bhp. It depends how the car was run - full 4wd, partial 4wd or 2wd also.

    Also, torque is torque and generally no differentialtion is made between wheel torque and flywheel torque- the RR torque figure is THE torque figure and in which case it's low - as reflected by your own VAGCOM runs and previous dyno runs.


    [/ QUOTE ]

    I know David. When they said "just add 40", I didn't like it. It's not exact enough for my liking.

    I know the figures look high AND that losses on rolling roads are usually between 60-80bhp. But this is a different kind of rolling road. And they say very accurate, based on the cars they have had on it.

    It's one of those rolling roads where the wheels of your car sit on the drum of the rollers, not in between two sets of rollers for each wheel. Car looks very precarious when on there.

    So I think there may actually be less friction/resistance between wheel and roller anyway, hence why the lower figure to "add".

    Regarding torque. Isn't torque proportional to BHP? If so, if you loose bhp through the drive train, wouldn't you loose torque too?

    Personally, I know I have used VAG-COM to log torque, and thus work out BHP. Which is lower than what the car should produce. But we've always questioned how accurate that method is.

    [ QUOTE ]

    Did they log boost?

    [/ QUOTE ]
    No

    [ QUOTE ]

    Did they / can they log req throttle with actual throttle position?

    [/ QUOTE ]
    Not sure.

    [ QUOTE ]
    a faulty TB will give hesitation and low power potentially

    [/ QUOTE ]
    I know but how do I get it checked.

    [ QUOTE ]
    ... What about logging misfires, fuelling, mixture etc....

    [/ QUOTE ]
    Logged loads. But nothing is showing.

    [ QUOTE ]

    I'm still stumped for a more definitive solution though [img]/ubbthreads/images/graemlins/frown.gif[/img]

    [/ QUOTE ]
    So am I and everyone I have spoken too.

    Cheers

    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Some top'o' the head thoughts:

    Can the throttle potentiometer on a DBW car give jittery readings that might result in jerky idle? Just a thought.

    My A3 was throttle-cable and had a jerky idle. When I had the throttle body cleaned, it helped, but not for long. Getting a new MAF might have helped too, but I did that not long before I sold the car.
    I remember the guy showing me where to look on the throttle body to see how much travel the valve had - you can see a metal disc on the outside, with a pie-shaped wedge sticking out, which hits parts on the outside of the main throttle body to control the min/max limits of the valve.

    He basically said that when gunked up, the valve doesn't have all the travel it needs, and can't maintain the fine control that it wants to, hence the jerkiness. I don't know whether the throttle body valve control is the same on DBW cars.

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    Re: Hesitation and Can I believe this Rolling Road Figure?


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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Thanks for your thoughts bk.

    It is slightly different on DBW cars. I have had the TB off, cleaned it, re-fitted, and done an electronic adaptation to reset it. But doesn't mean there isn't a problem with it - there could be. It's just how do I find out - there are no errors in VAG-COM.

    The problem is, it could be one of a hundred things, but no errors are being reported. [img]/ubbthreads/images/graemlins/frown.gif[/img]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    so you're still hunting it down eh AL? come-on Lad get a grip!

    looks like mine has surging on part throttle - nothing major but still enough for me to notice compared to my previous 2 S3's. I've changed the MAF, spark plugs, N75 valve but still no difference. Next will be the Lambda's when I find time.

    Stumped!

  9. #8
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    I know the figures look high AND that losses on rolling roads are usually between 60-80bhp. But this is a different kind of rolling road. And they say very accurate, based on the cars they have had on it.

    It's one of those rolling roads where the wheels of your car sit on the drum of the rollers, not in between two sets of rollers for each wheel. Car looks very precarious when on there.

    So I think there may actually be less friction/resistance between wheel and roller anyway, hence why the lower figure to "add".

    [/ QUOTE ]

    The bottom line is that your car should make the same figures on every road regardless of the method employed to measure power. If GTis rollers generate less drag, then this must be part of the cailbrations to make it accurate. To say that it creates less drag and therefore the wheel HP figures are greater is very misleading - your car should make x hp at the wheels on the road, on any dyno etc...

    Jim @ star has a device to measure actual throttle opening (i'm told) and it maps much quicker than vag-com so that momentary fluctuations missed by vagcom can be detected.

    I'd be really keen to see for myself what your car does, as I'm sure mine does it too, and most other S3s to a greater or lesser extent. Perhaps it relates to ECU revision and the speed with which they all react to inbound parameters?

  10. #9
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    My hesitation problem was caused by the fuel pump. I replaced it and all problems solved. Nothing else i had done prior to this made any difference. Unlikely in your case as mine was a 4bar pump running flat out at 4 bar... where as S3 is 5 bar pump @ 4bar. Changed mine for 5bar and as is well.

    Just thought i would mention it.

    Rich

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Rich, was your hesitation on part throttle or full?

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Simon. Are you back in an s3. What happened to the rs4?
    Al. Chill out. Just drive the thing. [img]/ubbthreads/images/graemlins/grin.gif[/img]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    Rich, was your hesitation on part throttle or full?

    [/ QUOTE ]

    Part throttle, off boost at around 2000-2500rpm

    Rich

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    Simon. Are you back in an s3. What happened to the rs4?


    [/ QUOTE ]

    Hello John. Yes back in S3 land again. Recently moved house and needed some extra pennies for an extension, plus with the prospect of falling RS4 residuals, decided it was time to sell back in June (got a very good price for my mint car considering the prices now). Really miss the car - power, flexibility and 'Noise'. Was starting to get peed with the attention it attracted.

    How many turbos you been through since I've been 'Away'? [img]/ubbthreads/images/graemlins/smile.gif[/img]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    [ QUOTE ]
    Rich, was your hesitation on part throttle or full?

    [/ QUOTE ]

    Part throttle, off boost at around 2000-2500rpm

    Rich

    [/ QUOTE ]

    hmm mines lower down the rev range too whilst on part throttle.

    How easy are these throttle bodies to swap? might tap Dunc up to swap his throttle body as a test.

  16. #15
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    [ QUOTE ]
    [ QUOTE ]
    Rich, was your hesitation on part throttle or full?

    [/ QUOTE ]

    Part throttle, off boost at around 2000-2500rpm

    Rich

    [/ QUOTE ]

    hmm mines lower down the rev range too whilst on part throttle.

    How easy are these throttle bodies to swap? might tap Dunc up to swap his throttle body as a test.

    [/ QUOTE ]

    Throttle body is a 10 min job to swap. It is definately worth a go. Fuel pump as i say is unlikely as an S3 wont be putting the strain on it that would cause it to knacker itself.

    Rich

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    John, Simon,

    Good to hear from you guys again.

    Hey, I'm chilled. Well, as chilled as I can be. Just tired of trying to find the problem.

    I can't ignore it though guys. It's got to be fixed. That's just me.

    On a recent trip down to Reading and back, the hesitation was happening very frequently. On a recent fast-ish drive round the peak district with the TT forum folks - this time the hesitation was happening all the time, in 3rd, 4th, and 5th and at various points in the rev range.

    David,

    Could you convince Jim @ Star to have a look at this problem? I have limited finances though I'm afraid.

    Cheers

    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]

    The bottom line is that your car should make the same figures on every road regardless of the method employed to measure power. If GTis rollers generate less drag, then this must be part of the cailbrations to make it accurate. To say that it creates less drag and therefore the wheel HP figures are greater is very misleading - your car should make x hp at the wheels on the road, on any dyno etc...

    [/ QUOTE ]

    Just to be clear. GTI didn't say it creates less drag. That was my theory, due to the suggestion of adding 40 to the bhp. Where on any other rolling road, you tend to add about 60-80bhp, like you said.

    I agree with you, the car should put out at the wheels the same power regardless of rollers or road.

    I'm confused, I'm no expert on the various types of rolling roads. But there is obviously some difference.

    Cheers

    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Just been looking through some of my logging which I performed for Wak.

    He has been very helpful, trying to help me analyse the logs and get to the route of the problem. Unfortunately, the logs don't show anything - everything looks like it is performing fine.

    The runs which I performed were done on the 18-Sep, the day before the car was at Awesome. Air mass flow was consistantly in the region of 180-189g/s at 5600-6100 rpm on a 3rd gear pull. I've only just properly read Wak's comments, he suggests that a reading of 189g/s equates to approx 237bhp....which in his experience is perfectly possible for a standard car as they loosen up. He's seen it before.

    Based on that....the day after, at Awesome, they suggest that my car has 195bhp + approx 40bhp = 235bhp.

    Coincidence? Maybe. Or maybe, Wak and Awesome are both right.

    Just thought I'd share that. Doesn't explain the hesitation though.

    Cheers

    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    This is when you find out you've got a twitchy nerve in your right leg, and it's wobbling on the throttle all the time. [img]/ubbthreads/images/graemlins/smile.gif[/img]

  21. #20
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    This is when you find out you've got a twitchy nerve in your right leg, and it's wobbling on the throttle all the time. [img]/ubbthreads/images/graemlins/smile.gif[/img]

    [/ QUOTE ]

    hahahahaha [img]/ubbthreads/images/graemlins/grin.gif[/img]

  22. #21
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]

    The runs which I performed were done on the 18-Sep, the day before the car was at Awesome. Air mass flow was consistantly in the region of 180-189g/s at 5600-6100 rpm on a 3rd gear pull. I've only just properly read Wak's comments, he suggests that a reading of 189g/s equates to approx 237bhp....which in his experience is perfectly possible for a standard car as they loosen up. He's seen it before.

    Based on that....the day after, at Awesome, they suggest that my car has 195bhp + approx 40bhp = 235bhp.

    Coincidence? Maybe. Or maybe, Wak and Awesome are both right.



    [/ QUOTE ]

    ...and I don't for one minute believe a standard car produces 237BHP genuine on an accurate dyno.

    Every car I've ever seen run has been around 225 or slightly less...210s tend to make slightly more...the difference in boost between a 210 and a 225 does not equal 15BHP...the truth appears to be that the 210s are 210BHP genuine...whereas 225s are 225 PS at best.

    But 237BHP standard...I doubt it.

    For the record...my 'strong' 210 made 208BHP as standard!



    ...and to add my thoughts on peak MAF sensor readings...
    I've logged standard MAF, de-screened MAF, Samco inlet pipe, modded airbox and K&N panel filter all in different combinations and all have showed different airfolw readings...some better...some not where you would expect better...
    None, however, have actually translated a theoretical increase in MAF flow to a BHP increase! Not one...

    In fact, my MAF airfolw peak went down with a modded airbox and K&N filter...the engine made the same power but slightly better torque...and felt much better on the 'ass dyno'.
    Not what should have happened according to the MAF flow!

    Just my comments AL...fuel to the fire and all that...

  23. #22
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    Every car I've ever seen run has been around 225 or slightly less...210s tend to make slightly more...the difference in boost between a 210 and a 225 does not equal 15BHP...the truth appears to be that the 210s are 210BHP genuine...whereas 225s are 225 PS at best.

    But 237BHP standard...I doubt it.

    For the record...my 'strong' 210 made 208BHP as standard!


    [/ QUOTE ]
    I believe the quoted 210 and 225 are both PS, VAG being German and all. I know the 210 Leon CR's were quoted as 210 PS.

    210 PS * 0.9863201652997627 = 207.1 BHP
    (conversion formula from wikipedia)

    So 208 BHP is about right for a "strong" one.

    225 PS * 0.9863201652997627 = 221.9 bhp for what it's worth.

    [edit] I presumed the 237 BHP figure was a chipped one... could be about right for a mild chip, or a slightly sick car. [/edit]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Glen,

    Always appreciate your opinion on this stuff. As I do from anyone who has years of experience.

    Like I said, I too, find it hard to believe. And butt-dyno...it doesn't feel like the car has 235-237bhp.

    I really haven't progressed solving the real problem, and at the same time, may have wasted 60 quid having the car dyno'd.

    Timbo,

    Car is absolutely standard. No chip.


    Cheers

    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?



    in November with very cold temperatures.

    and from Ross-Techs site.
    " Here's a good sanity check for the status of your MAF. Do a full-throttle run all the way to redline in a single gear (second works fine). Group 002 usually shows air mass in g/s. Your peak airflow should be roughly 0.80 times your horsepower. So, if you have a stock 150 hp 1.8T, expect around 120 g/s. If you see significantly less than that, you MAF may be on the way out. This still works if you are chipped, but "race" programs may make more power through timing, rather than airflow. Therefore, take all readings with a grain of salt."

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]


    How many turbos you been through since I've been 'Away'? [img]/ubbthreads/images/graemlins/smile.gif[/img]

    [/ QUOTE ]

    ooh. One or two. Plus an engine of course. Rod through block. Then burnt out a valve on cylinder 2 on the new engine.
    Now on low comp pistons, pauter rods, ported, polished big port head, vf34 20 housing, and the cars gone mental. 60-100 in third of around 5 seconds. Need to get a bigger turbo now. Another 500rpm of lag might be alright [img]/ubbthreads/images/graemlins/grin.gif[/img]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Alright Al,
    Still not got to the bottom of the problem eh!

    Have you ever thought of saying sod it and moving on?

    JamS3 - had a similar problem (down on power) and couldnt resolve it. He tried changing all sorts, MAF, coilpacks, sensors galore. Luckily he befriended a guy at the dealership, which saved him a few .
    In the end he said sod it and has a nice new Dolphin Grey S3 instead of a poorly Red one.
    Just a thought before you keep on throwing money at it. It could go on forever. [img]/ubbthreads/images/graemlins/bang.gif[/img]

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Hi Paul!

    Good to see you are still around. [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

    It's not a bad idea swapping for another S3 or even a different car all together. But...when you change, you could inherit a car with similar or worse problems. But if you are lucky I guess you could get one with no problems. That's my view. At the very least - I know where I am with this one...I know whats been changed etc.

    Plus I can't afford to change cars...house, saving to get married etc. I know you know all about that stuff! [img]/ubbthreads/images/graemlins/grin.gif[/img]


    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Yep still around Al. Just tend to read, rather than post a lot now.
    Theres still Audi blood running through me, that'll never change. Quite like the A3 Sportback (read "Pram"back) so I may be tempted in a few months.

    I here what your saying about your S3 Al. I suppose its just annoying when your running out of options, without throwing fistfulls of cash at it over and over again.
    As long as your still enjoying the car mate thats all that matters.
    Its just that if the problem was happening to me, I'd be waiting for it to hesitate everytime I drove it and it would drive me nuts. I'd end up hating it and getting rid.

    [ QUOTE ]
    house, saving to get married etc. I know you know all about that stuff!

    [/ QUOTE ]

    Yep definately in the club now, even got the dog and kid.
    As a joke when I sold the S3 and bought the Leon, the wife even bought me a pipe and some paisley slippers.
    I got some lovely slippers and a diesel astravan, she got a brand new Leon Cupra R. Work that one out. [img]/ubbthreads/images/graemlins/bang.gif[/img]

    I wouldnt change it though. [img]/ubbthreads/images/graemlins/love_4.gif[/img]

    Good luck in your quest, hope you sort out the problem. [img]/ubbthreads/images/graemlins/beerchug.gif[/img]

  30. #29
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Well fellas, just thought I'd post an update on this following the cars service and running it for a week or two on motorway driving etc.

    The verdict is, hesitation is still occurs, but is happening less now. It's only happened once or twice this week. And one of those instances I am unsure about.

    So the service may have helped (new plugs, new oil, air filter etc.) or it could perhaps be something to do with the lower ambient and intake temps. What with the weather being cooler now.

    Going to order a new MAF I think, just to compare against.

    AL

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Al have you ever got round to replacing the lambda sensors? Or logging the values from these, it gets on my nerves eveyone suspecting the MAF sensor immediately. It can throw you in the wrong direction.

    Also have you thought about the coil packs degrading, i had one blow on me again the other day, about 2 yrs ago they were changed by roadside due to them breaking down. I did not think i would have any problems again but there you go.

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    What about the ECU ? I know it's an expensive thing to try, but sound like you done everything else ?

  33. #32
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Thanks for the suggestions again guys.

    My hesitation problem could also be caused by this...

    Power loss / clutch

    I really need to get my car down to somewhere like AmD.

    We currently have possibilities of:-

    MAF
    Fuel Pump
    Fuel Pressure reg
    Throttle Body
    Throttle position sensors
    Clutch
    Dual Mass Fly Wheel

    [img]/ubbthreads/images/graemlins/frown.gif[/img]

    AL

  34. #33
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]


    On a recent trip down to Reading and back, the hesitation was happening very frequently. On a recent fast-ish drive round the peak district with the TT forum folks - this time the hesitation was happening all the time, in 3rd, 4th, and 5th and at various points in the rev range.

    David,

    Could you convince Jim @ Star to have a look at this problem? I have limited finances though I'm afraid.

    Cheers

    AL

    [/ QUOTE ]

    Al - I'm having similar problems i think. Car was running perfectly, no hesitation, smooth acceleration etc... had it remapped at AMD and a new Diverter Valve and now it's got some sort of hesitation. If i hold revs at anywhere between say 3,000 and 4,500 rpm for a second or so and then ease off i kind of get a hesitation, like a jump, which feels a bit like fuel flow. Passengers can't feel it, just me. And I can feel it through the accelerator... any ideas? I've been back to AMD and been VAGCOMd which didn't show anything, i've a newish MAF, they've replaced the DV which they thought could be sticking and suggested it could be the N75? I'm booked back in to get it on the rollers soon - anyone got any suggestions of what it could be? Could it be fuel flow do you reckon? Maybe the remap?????
    Help! It's driving me mad (excuse the pun)!
    [img]/ubbthreads/images/graemlins/noidea.gif[/img]

  35. #34
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    TQS,

    Hi mate. Your problem sounds slightly different to mine. How big is this jump and what does it feel like through the accelerator?

    I have heard these hesitations could be caused by fuel supply and/or throttle bodies. But similarly it could be caused by a dodgy plug or coil pack. There is just so much that can go wrong.

    If you've changed the MAF and DV, I would then suggest replacing the N75, and also clean your throttle body and do a throttle body adaptation aftwards. Then see how it goes.

    As my experience shows, its trial and error with this stuff. More a matter of eliminate possible items by replacing them, test after each individual replacement item.

    Its a bloody nightmare unfortunately.

    AL

    PS: how much did AmD charge for the investigation. PM me if you do not wish to post the amount etc.

  36. #35
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Hi - it's not a big jump like a lunge or anything, just a slight gap in deceleration and it's only the driver that can feel it 'underfoot'... just a bit strange that it's only happened post remap/dv replacement... AmD have been really helpful though so far

  37. #36
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    TQS

    I have this also. So does my mate with a standard S3.

    I thought it was normal..

    Perhaps everyone else can give it a try?

    Hold the revs about 4000 for a few secs (as if you are waiting to floor it) and then floor it... What happens?

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Also try holding about 4k revs for a few seconds and then easing your foot off the accelerator (which is when it happens for me) - there';s kind of like a gap in fuel flow and it feels to me like a bit of a spli-second judder/surge before deccelerating smoothly. It doesn't always happen but it is noticeable on longer journeys.

    I don't think this is normal given it only started happening to me post remap.

    Also, my mpg has seriously dropped on a motorway run from over 30mpg to barely 25mpg which makes me think it could be fuel related as i was told by all that motorway mpg should improve if anything!

  39. #38
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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    [ QUOTE ]
    Rich, was your hesitation on part throttle or full?

    [/ QUOTE ]

    Part throttle, off boost at around 2000-2500rpm

    Rich

    [/ QUOTE ]

    Hi, I am an imposter here! I come from the newer A3 board, current car from today will be a 2.0T S-line quattro, right, this problem you have, I also own an old workhorse in the shape of a tuned 300ish hp T5. There was a lot of talk on the Volvo website about EXACTLY this type of missfire, eventually they solved it by fitting a new lambda sensor, the "theory" behind this was that the lambda was out of spec causing the ECU to have trouble in believing the difference between the signals from MAF/throttle position and lambda, I would be tempted to try a new lambda

    on the rolling road stuff, I have a lot of experience on RR's, none are the same, we used to use AMD at the village site with Geoff and also at the time the car was being pulled into Porsche GB quite frequently for power tests, there was a lot of speculation the PGB had "upped" the calibration because at that time they were having a lot of trouble with 993RS's not making the quoted 300bhp mark. Another very important aspect for Turbo cars is trying to keep the intercoolers cool on the rolling road, very hard to get a genuine air flow through them in my experience. The easiest RR we used to use was a Dyno jet inertia type, very repeatable and figures were very close to manufactures claims, but I have never seen a FWD one, can't the FWD be switched off like the TT?

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    Had something about the same with a Nissan. It turned out to be the a doggy connector to the MAF. A real pain to find. Also my brother had something similar which was cured by taking the earth wire from the MAF straight to the chassis, another common Nissan fault.

    The Lambda could have some contamination on its surface. So before trying a new one take the one out you have and stick it in half a lemon over night. Believe it or not it will come out looking like new.

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    Re: Hesitation and Can I believe this Rolling Road Figure?

    [ QUOTE ]
    There was a lot of talk on the Volvo website about EXACTLY this type of missfire, eventually they solved it by fitting a new lambda sensor, the "theory" behind this was that the lambda was out of spec causing the ECU to have trouble in believing the difference between the signals from MAF/throttle position and lambda, I would be tempted to try a new lambda


    [/ QUOTE ]

    Interesting...
    But lambda is only of use in closed loop mode below about 2500RPM due to the narrow operating band of the VAG lambda sensors...or so I believe.

    ECU closed loop control operates where the lambda can measure the mixture over a fairly small range - hence idle to approx 2500RPM.

    I had a lambda sensor go bad on my golf GTI and idle was bad, town driving was rough and MPG was awful, but above 2500 it was perfect and made perfect power on the rollers with no hesitation above the open loop changeover point.

    As far as I know, the S3 also only uses lambda in closed loop mode below approx 2500RPM although ther second lambda sensor IS used to bring in a check light and possible 'limp' mode if the post cat measurement goes way out of spec...but again, I believe this to be a narrow band type that is set to measure post-cat differences in mixture that happen to be within it's narrow band of measurement.

    Hence, I can't see the lambda sensor causing a missfire like hesitation at 4000+ RPM...I may be wrong though.

    Lambda is easy to map with VAG-Com, so it shouldn't be too hard to spot irregularities.

 

 
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