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Discussion Starter #1
Hi folks,

I have a Golf TDI with a manual transmission. Love it, BTW.

Today, while the car was fully warmed up, I noticed that, for about 10 minutes or so, the car became dramatically more responsive, as though the turbo suddenly had zero lag whatsoever.

Anyone with a similar engine/transmission set up probably knows that, unless you're always keeping the revs high, there's a pretty noticeable turbo lag. Plant the pedal at, say 2200 RPM in 2nd gear, and not much happens for a beat before the turbo spools up and wafts you forward. And it's even more noticeable in the super-short 1st gear, where by the time the turbo wakes up, the tack is zinging past 3000 RPM and it's time to shift anyway.

But for a few minutes today, I was really surprised to find that, even in 1st gear and after letting out the clutch gently, I could plant the pedal and the engine pulled hard and instantaneously with zero lag from as low as 1500 RPM. Same in other gears, though the effect was most noticeable in 1st and 2nd gears. I tried lugging the engine around to see how low I could get the turbo to spool up, and shockingly, it was pulling hard by 1300 RPM or so, not the usual 1800-2000.

Also, the little shift "suggestion" on the MFI, which recommends and upshift or downshift depending on driving conditions, was behaving very differently. Cruising at 1800-2000 RPM in 3rd or 4th, the indicator was suggesting a downshift. Normally, any cruising over 1500 RPM results in a suggested upshift.

Finally, it was idling a little rough during this period. It shuttered lightly every once in a while in no particular pattern, like a cylinder was misfiring occasionally.


Anyway, it was great fun for about 5-10 minutes, but then the car started behaving normally and did so for the rest of the 40 minute drive.

This happened when the car was fully warmed up, 300 miles into a tank of diesel with 1635 miles on the odometer.

Any ideas? I thought maybe it was burning off stuff in the particulate filter, thus changing the fuel mapping, but I'd be surprised if that would change the engine dynamics so much.

Sorry for the long post, I just wanted to cover all the bases.
 

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It sounds like it was in a regen cycle. The ECM increases the boost a few psi to make up for it. Or maybe you're just in a good mood and was really enjoying the car :)
 

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Did the temperature change? It been colder or warmer today? That's the single biggest thing i notice on my car here in FL, where it'll be 45 in the morning and 70 by noon. That temperature range really makes a difference in performance and fuel economy.
 

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Discussion Starter #4
It sounds like it was in a regen cycle. The ECM increases the boost a few psi to make up for it. Or maybe you're just in a good mood and was really enjoying the car :)
Heh, I figured a few would assume that it was just me feeling sporty. But I swear, I have a finely calibrated but, and this was way out of the ordinary. Regen cycle sounds most likely, but I really wonder how in the world the regen cycle makes the turbo miraculously lag-free. And it wasn't a case of increased boost, necessarily, beause it was the instantaneous punch it had at very low RPM that I noticed. I was driving with my usual zeal, and from 3:30 PM to about 3:40 pm, there was a HUGE difference in turbo performance and response. Before and after that time, it drove normally.
 

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Did the temperature change? It been colder or warmer today? That's the single biggest thing i notice on my car here in FL, where it'll be 45 in the morning and 70 by noon. That temperature range really makes a difference in performance and fuel economy.
Yeah, temperature has played a big role in torque response in other cars I've driven. My previous car, a 2000 Mazda Protege ES, had wheel-spinning torque when it was cold, and was pretty much gutless before 3500 RPM when it was warm.

But I don't think this is the case with the TDI. It'd been ass-cold here in Chicago for a few weeks. It was 25 degrees F or so that day, and had been about the same for the past week. And unlike other gas-fired cars I've driven for the past 15 years, the TDI seems like it has poor torque response when its cold.
 

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Today, while the car was fully warmed up, I noticed that, for about 10 minutes or so, the car became dramatically more responsive, as though the turbo suddenly had zero lag whatsoever.
FWIW, when I forced an active regen on 2 different cars/owners, one person said the car felt sluggish. The other said it suddenly felt more powerful. It could just be related to how they normally drive or personal perception. And some cars just feel a little different too.
 

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Discussion Starter #8
Shift suggestion on MFI?

I have a 2010 model, does that exist on my model year or is that a 2011 feature?
On my 2011, in the top right of the screen between the gauges, it tells me what gear I'm currently in, while accelerating or decelerating in-gear, and when cruising, it suggests an upshift or downshift if I'm not it the gear it thinks I should be in for best fuel economy. Useful, I guess, but also kind of annoying because, in the city driving I'm usually doing, I'm almost never able to cruise at a constant speed. That woudln't be a problem, except the suggested gear always puts me at 1200-1300 RPM, where there's no boost to pull me up a few MPH, so i end up up and downshifting more than I need to just to vary my speed by 5 MPH.

FWIW, when I forced an active regen on 2 different cars/owners, one person said the car felt sluggish. The other said it suddenly felt more powerful. It could just be related to how they normally drive or personal perception. And some cars just feel a little different too.
Totally appreciate the response, but I do want to emphasize that it definitely wasn't personal perception, or my mood, or anything else like that. The car behaved normally before and after the "event." But for about 10 minutes, it was dramatically different as described above. And the increased response was repeatable. I spent time probing the engine's torque response over and over, and each time found that boost spooled instantaneously at VERY low RPM.

Here's an example: I'd let out the clutch gently to get the car rolling to less than 10 MPH and coast there for a second with little or no throttle input (so no boost), which was about 1500 RPM. Then stab the pedal about half way. The result was instant, wheel-spinning torque that seemed to plateau from 1500-3000 RPM. I repeated this as every stoplight for several minutes, along with experimenting with torque response in higher gears at very, very low RPM. Normally, this exact scenario would result in that characteristic rubber-band torque response in which the very short first gear allows the engine to rev faster than the turbo can spool. Thus, full boost doesn't come on until the tach is swinging past 3000 RPM and it's time to shift anyway.

Anyway it's not like I'm concerned or anything. Just very curious. How might a DPF regen cycle increase turbo response at low RPM?
 

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The ECU increases boost during an active regen. You can tell when the car is doing an active regen through VCDS but there's no light or other indicator. The radiator fan will run fast if you're stopped at a light or just shut the engine off and you may smell a burning rubber smell.
 

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Cold weather mileage on my 2011 Golf TDI

On a Christmas trip from New Orleans to St Louis I watched my mpg slowly decrease from 46.1 mpg highway at 64 degrees (F) to 40.1 mpg highway at 30 degrees (F) as I approached St Louis.
On the return trip the reverse happened. I started in St Louis at 39.6 mpg at 28 degrees (F) and ended the trip in New Orleans at 43.1 mpg at 45 degrees (F).

Have no clue as to why the exact reason for the mileage differences except perhaps the terrain is uphill going to St Louis and downhill returning to New Orleans
 
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