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Discussion Starter · #1 ·
Posted this in general, didn't get any responses...

Between 40-70 I get a very slight repeated hesitation or stumble, once every second or so, when I'm holding constant speed. Coasting or accelerating will make it go away.

No CEL, no codes. Not related to road surface...

Fuel economy seems to be good.

Thoughts appreciated...

110K miles.
 

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And you have reset he gearbox?
 

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When you say 'constant speed' I assume you mean you are using cruise control and there is no other reason (slight uphill or down) for the ECU to adjust power?
 

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When was the last time you replaced fuel filter?
 

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Discussion Starter · #5 ·
And you have reset he gearbox?
No, I have not reset the gearbox. I will do so today.

However, the tach is rock steady when I'm experiencing the hesitation.
 

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Discussion Starter · #6 ·
When you say 'constant speed' I assume you mean you are using cruise control and there is no other reason (slight uphill or down) for the ECU to adjust power?
Not actually using cruise, just a steady foot. Flat road, no reason for ECU to adjust. The hesitation is fairly rhythmic, perhaps once a second or so...
 

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Discussion Starter · #7 ·
When was the last time you replaced fuel filter?
Fuel filter was replaced just over a year ago, about 15K miles, at the 100K mile service.
 

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That is about the speed at steady state, that I have noticed it in my car as well. I hooked up my VCDS and the power to maintain speed is minimal, so the waste gate on the turbo opens and closes. absolutely normal. if you set the cruise at the same speed, you will never feel it again.
 

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Discussion Starter · #9 ·
That is about the speed at steady state, that I have noticed it in my car as well. I hooked up my VCDS and the power to maintain speed is minimal, so the waste gate on the turbo opens and closes. absolutely normal. if you set the cruise at the same speed, you will never feel it again.
Interesting.

Why does the waste gate opening and closing cause the stumble?

Why would engaging cruise keep it from happening?
 

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It isn't a stumble like a misfire in a gas car. The diesel engine requires boost from the turbo to produce power. So when the boost is dumped because the engine signals no need for power, there is a noticeable drop when you are attempting to maintain a moderate speed. I have felt it in every one of my past 6 diesels.

The reason it isn't felt with the cruise on, is because the cruise logic is incorporated within the ECU logic for power requirement. This is another reason I'm amazed by the VW.
 

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Discussion Starter · #11 ·
It isn't a stumble like a misfire in a gas car. The diesel engine requires boost from the turbo to produce power. So when the boost is dumped because the engine signals no need for power, there is a noticeable drop when you are attempting to maintain a moderate speed. I have felt it in every one of my past 6 diesels.

The reason it isn't felt with the cruise on, is because the cruise logic is incorporated within the ECU logic for power requirement. This is another reason I'm amazed by the VW.
Thanks. I don't normally use cruise. I'll test that on our next long drive...

That stumble is annoying!
 

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I'm having same issue with my, except mine (2006 V10 180K miles) stutters or shifts hard with mild acceleration up hill or on flat surface. If I keep in 3rd gear, it doesn't seem to do it. Brought to dealer, lead tech said #6 injector is out, consistent with engine light that popped on. Also said it could be a valve in the transmission. Getting the former done next week, I'll update and let you know if it worked. My fuel filter was replaced recently...

BTW, you guys have a favorite place to get both new and used parts? I'm a newbie to the forum, and to Tregs
 

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I get that sometimes too.. It happened yesterday going up hill, maybe 50-ish miles per hour. In my case I figure it was the ECU pulling timing because the fuel was getting hot. I was about 1/16th below a quarter tank of fuel and the ambient outside temp was around 100.
 

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I get that sometimes too.. It happened yesterday going up hill, maybe 50-ish miles per hour. In my case I figure it was the ECU pulling timing because the fuel was getting hot. I was about 1/16th below a quarter tank of fuel and the ambient outside temp was around 100.
not possible
 

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Change the fuel filter. The agents almost never do it.
 

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I get that sometimes too.. It happened yesterday going up hill, maybe 50-ish miles per hour. In my case I figure it was the ECU pulling timing because the fuel was getting hot. I was about 1/16th below a quarter tank of fuel and the ambient outside temp was around 100.
not possible
uhh ok.. why not? every other diesel I have owned has been able to do this...
 

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uhh ok.. why not? every other diesel I have owned has been able to do this...
even if it did you would never physically feel it, nor is there any proof that it even does...do you have documentation to show this? Ive ran this tank almost completely empty 10-20 times its never hesitated or stumbled. The more likely candidate is regen, nothing to do with fuel heat at all.....im guessing your another believer that going below 1/4 blows fuel pumps as well.....ive tried that theory its not possible..225k on a cr 2.0 with 90% of tanks below fuel light never a pump issue....if it were true then it would happen you cannot claim it does when someone can do it time after time after time. Heat is either going to kill it or not, or im the luckiest guy alive 200 times. Water and poor fuel quality kill hpfp nothing more, running low on fuel is just fine....runing out mind you i wouldnt advise but ive never been there.

It could even be your fuel source, having driven as much as i have in common rails i can safely say every tank of american fuel i used made my car act different, if it was stock it would miss and surge...tuned it would smoke like a train....strong believer the fuel quality is just not upheld enough down there, fuel up here seems to be better and more consistent, this is also shown by the huge difference in hpfp failures there and up here
 

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even if it did you would never physically feel it, nor is there any proof that it even does...do you have documentation to show this? Ive ran this tank almost completely empty 10-20 times its never hesitated or stumbled. The more likely candidate is regen, nothing to do with fuel heat at all.....im guessing your another believer that going below 1/4 blows fuel pumps as well.....ive tried that theory its not possible..225k on a cr 2.0 with 90% of tanks below fuel light never a pump issue....if it were true then it would happen you cannot claim it does when someone can do it time after time after time. Heat is either going to kill it or not, or im the luckiest guy alive 200 times. Water and poor fuel quality kill hpfp nothing more, running low on fuel is just fine....runing out mind you i wouldnt advise but ive never been there.

It could even be your fuel source, having driven as much as i have in common rails i can safely say every tank of american fuel i used made my car act different, if it was stock it would miss and surge...tuned it would smoke like a train....strong believer the fuel quality is just not upheld enough down there, fuel up here seems to be better and more consistent, this is also shown by the huge difference in hpfp failures there and up here
hmm...I think you need to learn about how the diesel operates more. The VAG-COM has options to set your injecttor timing according to fuel temp, so fuel temperature is very relevant to peak engine efficiency.

Ross-Tech: VAG-COM: TDI VAG-COM Info

The only time I have ever felt my diesel vehicles hesitate was on hot days with fuel levels under 1/4 tank. the diesel fuel is also used to cool the injector pump (tandem pump on the TDI) and if the fuel temp gets too hot, the engine will pull back timing to preserve the pump, it's that simple. I don't often drive with fuel less then 1/8 a tank (in the red zone) for just this reason. If I have to, I try to stay off the boost and I never use a lot of throttle to keep the temps down. As you said, it could be a fuel filter, which is possible. But also an old fuel filter will make this problem worse, and I am due for a fuel filter on the next oil change.
 

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i never said anything about a fuel filter...and i know plenty how tdis work, this is my 3rd and none were ever just left stock. My tuner who is very skilled and poplar agrees with me you would never feel the timing.....nor does it make any sense to drive differently when your below 1/4 tank or 1/8 tank...stay off the boost lol thats impossible first off.

the fuel pumps are just fine...heat damaging them is unproven and ive never seen other wise....i go into the so called red every tank...i guess my touareg and jettas had different cooling systems then because you think id see a failure by now.....and i never baby my tdis thats how you ruin a tdi anyway
 
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