Bi-Turbo Turbo Lag?

[ChuckMountain]

So I have myself an A6 Saloon Black Edition Bi-Turbo 320ps car which I have had for just over 2 months and done 2,500 miles or so and am mainly loving it. (Even the fuel economy is not too bad compared to my 2.0 Multitronic ;) )

I have one small concern and I don't if its just my imagination or not.

Sometimes it seems considerably quicker at the lower end of the speed end in say the 0-40 section than others. Normally the driver knows when he puts his foot down that the car will go and you expect the acceleration. Sometimes though I am unprepared for how "quick" it can be and accelerates through the lower end of the engine RPM very quickly (does not change gear). Other times it seems "considerably" slower not as much push back in the seat etc. Not sure how this is for example impacting 0-60 time.

Am I imagining it or not? I can't work out if its something going on with the gearbox deciding to change down and momentary delay or there is something more fundamental like the small turbo isn't providing the necessary boost it should do.

I do change Car modes and often vary between Economy, Auto and Dynamic and what I would say is that Economy can often get to a higher speed, not necessarily quicker but because there is less engine braking when you take your foot off the throttle so its natural momentum will take it quicker.

I have VCDS and there are no relevant faults flagged on error scan and have enabled the lap timer and boost appears to be displaying at bottom end.

Anybody got any tips or ideas of what to try? My nearest Audi garage is a good 30 mins away and I am sure if I took in they would test it but possibly not notice because overall it still seems quick.

[Scott K]

It's the gearbox. If you kick down it can take a second to decide which gear to go in then it takes off like a scalded cat. You can test it by pushing the gearstick to manual and using the paddles. Coming to a junction, I now knock the box into S so there is less hesitation. It is frustrating but you do get used to it. With a bit of luck they may upgrade the software.

[ChuckMountain]

Thanks Scott, sorry I should have added have tried it in manual, sports and "normal" and though there is a difference in the way the gear box behaves it doesn't seem to make much difference to the scenario.

If it stays in gear and say accelerates from 1,500 - 2,000 to higher revs it seems "considerably" slower at the lower end sometimes, there is less force back into seat what appears to be a noticeable difference. I appreciate that different car modes have different engine responses but putting in sports mode or manual when I notice it does not seem to improve it.

Again it could be my imagination or I am getting used to it, but when picking my son up from football it was a lot quicker at the bottom end from of the mark. To the point where he told me to stop accelerating all the time and we generally don't get above 40 on that route home) So off the line it sometimes seems quicker and for a car that does 0-62 in 5.0 secs the start 0-30 will be important.

[Scott K]

With the twin turbo, the smaller turbo comes in about 1500 rpm and eventually the bigger takes over completely at 4500rpm. Not sure if it is turbo lag at the lower end. I never drive mine in Eco as I tried it once and the mpg seemed to be the same-not sure if that could be an issue as eco makes it change up sooner. In sport there should definitely see a difference.

There is a facility in VCDS to hook it while you are driving and see the boost etc. I have never done it but that may show up any flat spots.

Cheers, Scott

[ChuckMountain]

Will have to have a play or rather get somebody to have a play whilst I am driving and see if we can spot how to do the monitoring.

I appreciate the twin turbo just wondering if the small one is pushing as much as it should.

I quite like the Eco mode not for the economy which is marginal if anything but just for a different drive mode if you just want to tootle round town. Also when the wife drives the car it seems to find itself in that mode automatically and I haven't shown her you can change it ;)

[Chesterfield313]

It really doesn't sound like there is anything wrong to me. Sometimes mine feels faster than others and it can be any number of factors that make a difference. The real shove in the back feeling is from a wallop of torque in one go. However, sometimes if in the right gears at the right revs the power will be delivered in a much more linear factor, more like a petrol, it will feel slower, but in reality is probably slightly faster.

You soon get used to the different scenarios and know when it will do what.

[ukgroucho]

There is a facility in VCDS to hook it while you are driving and see the boost etc. I have never done it but that may show up any flat spots.

You don't need to do that. If you can enable the lap counter screen in the DIS with VCDS (I THINK you may need colour DIS for this) then you get a turbo boost gauge that runs up the side of the rev counter. And oil temp (top right) and F1 style gear shift indicator bars across the top if you are in manual change mode (bit of a chocolate teapot unless you intend to try a track day but entertaining nonetheless :) ).

28807

[Uberman]

Using a graph in VCDS will help you understand better if you have an issue- Boost pressure, RPM and Speed trends should be enough to see if there are differing patterns that might explain the different car feel. High speed sampling is the best but sometimes crashes the application.

Easy to do: Ross-Tech: VCDS: Tour: Generic OBD-II Screen (http://www.ross-tech.com/vcds/tour/obd-2.html)

Trick will be trying to separate it from gearbox lag, so some runs in manual to contrast might also prove useful. Probably some runs in manual and in 2nd gear will give you some decent data. All too easy to misinterpret data, the more runs you do the more any patterns should stand out though:confused:

[Fasteddy]

Hi I have experienced the same scenario and it seems to happen when the car is running the dpf cleaning mode in which coincides with the gearbox not changing to an higher gear as quickly (lower rpm) as normal and won't stay in an higher gear when decreasing speed
You'll notice if this happens by stopping switching ignition off and the dpf fan continues running for a period of time

[ChuckMountain]

Using a graph in VCDS will help you understand better if you have an issue- Boost pressure, RPM and Speed trends should be enough to see if there are differing patterns that might explain the different car feel. High speed sampling is the best but sometimes crashes the application.

Easy to do: Ross-Tech: VCDS: Tour: Generic OBD-II Screen (http://www.ross-tech.com/vcds/tour/obd-2.html)

Trick will be trying to separate it from gearbox lag, so some runs in manual to contrast might also prove useful. Probably some runs in manual and in 2nd gear will give you some decent data. All too easy to misinterpret data, the more runs you do the more any patterns should stand out though:confused:

Thanks I will give it a try and see with the OBD-II screen. I have the lap timer already engaged so can see the boost but I did wonder what drives the display and whether its actually the turbo reporting it or the software thinking it should be if that makes sense.


Hi I have experienced the same scenario and it seems to happen when the car is running the dpf cleaning mode in which coincides with the gearbox not changing to an higher gear as quickly (lower rpm) as normal and won't stay in an higher gear when decreasing speed
You'll notice if this happens by stopping switching ignition off and the dpf fan continues running for a period of time

Ah yes very good point, thinking about it the time I noticed it most was when it was doing DPF cleaning because my son also asked why the car was making a noise after we got out and locked it. Thinking about it the other times have probably been the same. In this case it doesn't appear to change as much. In this scenario it feels quicker in the 0-30 and more push back. Was this the same for you? Is the car quicker due to an increase in boost or delay compared to normal?

[Fasteddy]

I'd assume it's to do with the engine ecu and gearbox ecru when in Dpf mode where as you're travelling in a lower gear in auto mode
eg. When in cruise control 30mph the car will easily remain in 5th gear maybe reduce to 25mph before it drops to 4th however when in dpf mode it will stay in 4th maybe up to 35mph before it changes up an gear
so I'd imagine it would only be a perception that the car is quicker in dpf mode as you're already in a lower gear

[Rassi]

How is your fuel economy? Read about a BiTDI on a French forum that had appalling fuel economy and random lacklustre performance, which was traced to DPF regeneration every 200 miles or so, rather than 800 miles (+/-).

[ChuckMountain]

How is your fuel economy? Read about a BiTDI on a French forum that had appalling fuel economy and random lacklustre performance, which was traced to DPF regeneration every 200 miles or so, rather than 800 miles (+/-).

It's all relative I guess. I have something like 35-36mpg over 2,500 miles though need to check. I must admit I have a heavy right foot and at a lot of that mileage was in France at 80mph where I would get 38-40mpg or so. I am expecting it to go down a bit because I am doing a lot of short journeys at the moment so the tank is saying 475 miles full (was around 535-550 before local traffic) which is 73L compared to my old 2.0TDI mulitronic which was around 525 on a 65L and that was around 36mpg overall a much longer period.

I have never been anywhere close to the claims but to be honest you would have to drive slower than Miss Daisy to get them :)

I would say also that if you drive the car moderately or fast then you are not going to get anywhere near the status. I have had under 20mpg on one trip when I had my foot down ;)

[Scott K]

Your economy isn't too bad. Mine was about 38 mpg for the first 5000m and has now settled at 40 mpg. The computer reckons about 5% more but mine is worked out brim to brim.

[robbyg]

I think there are two elements to the answer IMHO.
1. during DPF regen it certainly hold back the gears and i agreed with fasteddy re 5th or 4th at 30 is an easy way to spot regen in progress. Obviously it will respond quicker and not need to kickdown if already in a lower gear.
2. (i beleive) one of the ways modern adaptive gearboxes operate is to measure how fast yo press the pedal. eg if i am driving at 30 then reach the end of the 30zone and it becomes national speed limit: in 5th ease the pedal slowly from 5% travel to maybe 50% it will stay in 5th and pull gently and smoothly using the lovely low down torque. move the pedal quicker from the same 5-50% and it will drop to 4th or 3rd and give it more beans. Jab the pedal hard to 50% and it will probably grab 2nd. How you drive makes a big difference to how the autobox respons. A jab=delay then big response, and easing = instant but smoother response.

[Bar Shaker]

It's also worth remembering that the gearbox learns your driving style.

If you very rarely ask for fast gear changes, it may learn to do them slowly and more smoothly.

I tend to use the paddles if I need to move quickly.