1Z with empty tank, surprisingly peppy!

Hello,
For a long time, I thought I was just imagining it, but it's actually true.
When I'm driving around with just a few liters of fuel left in the tank, my Audi 80 TDI seems to be noticeably faster than when it has, for example, 20 liters in the tank.
The engine responds more readily to the accelerator pedal, feels more powerful, and the turbo lag seems less noticeable. If I then add 15 or 20 liters of fuel (I never fill the tank completely; I usually only buy €20 worth), the engine feels slightly restricted.
Here are also two people who notice this:
http://www.motor-talk.de/t391685/f40/s/thread.html

Can someone please explain this technical context to me?

Thank you very much.
Regards,
Sausage blinkers.

That's really true, I have no idea why.

Hi,

I would say that's because when you're very familiar with a car, you become much more sensitive to things like acceleration and so on.

Refueling, unlike running a tank dry, causes a sudden weight change of perhaps 40 kilograms (for a full 45-liter tank). Even 20 liters weighs around 15-18 kilograms, which has a slight but likely noticeable effect on acceleration.

I've noticed this at ASV gas stations too, when I've filled up the tank and then driven away – it feels like the car is heavier than before, even though there might only be 5 liters of fuel in the tank.

Similarly, you can tell when more people are traveling or when heavy luggage is being loaded.

I think that's exactly the cause.

Best regards,

Jan.

No.
It can't be due to weight. Gaining or losing 20 kilograms is ridiculous! I don't even notice a difference when I put two cases of beer in the trunk.
I also notice the increased power when I take someone else with me.
The engine just feels different.
There must be another reason for that!
Could the fuel temperature perhaps have something to do with it?

But I'm definitely not the only one who notices this.

Best regards,

Hi,

"When I load a full case of Coca-Cola (15 kilograms of liquid plus maybe 2 kilograms for the bottles and the box), I definitely notice it in the relationship between acceleration and how much I press the gas pedal – it feels a bit slower."

Best regards,

Jan.

Jan6K wrote:

When I load a full case of Coca-Cola (15 kilograms of liquid + maybe 2 kilograms for the bottles and the box), I definitely notice it in the relationship between pressing the accelerator and the resulting acceleration - it feels a bit slower.

I also notice that the car feels "significantly" heavier immediately after refueling.

I've thought to myself more than once, "Oh dear, what kind of fuel did you put in there?"
However, in the subsequent DZR tests, the time was always within the normal range.

I also don't have a mechanical explanation for the observations...

Possible explanations would be:

- The temperature-mass adjustment is not perfectly aligned with the diesel temperature (when the diesel is cold and dense, less fuel is injected than what the mass would indicate).
-> Clarify by making the EDC believe it has a fixed temperature.

- Unexplained reason: Including the fuel level sensor... but then it should ALWAYS be slower when the tank is full.

For me, it sounds quite plausible and is especially easy to test.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hi,

I'm less inclined to believe that. If you start with 5-10 liters of remaining diesel and then drive maybe 3 km through the city (which is my usual refueling behavior), I don't think there would be a significant temperature increase in the tank; that fuel should therefore be at ambient temperature. Of course, the diesel from the underground tank might be slightly colder (or warmer in winter), but first, the old diesel needs to be drained from the filter and lines, so the effect wouldn't occur immediately.

We should pay attention to this in the winter; at that time, the effect shouldn't be present (if that's the cause) because there won't be any temperature difference.

I still believe in the importance of driver weight.

Best regards,

Jan.

Okay.

Then just take a quick photo from the gas station .

The gas station attendant won't be happy if you come barreling in from the platform with full torque .

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hi,

My friends would also give me a disapproving look if I were to speed through the 30 km/h zone in third gear.

Best regards,

Jan.

Hi,

I generally drive in a fuel-efficient manner. However, as soon as my girlfriend is in the car with me (she is very slim ), I have to change my driving style and rev the engine higher. I also notice the weight difference extremely after refueling.

Do you notice a weight difference of 1/25 to 1/30?
Soon, the performance will be changed by almost 3%. We, as AFN users, can already determine the outside temperature to within 3 degrees Celsius using just a popometer.

Surely, you'll notice the extra 20 liters in the tank, as the car noticeably slows down with an approximate 1.5% increase in weight.
You can clearly see that in Formula 1!
If the pilots receive 20 liters more fuel, they are actually 2/10 of a second slower on a circular track of approximately 5 km, and that's with a vehicle weight of "kill me" 700 kg.
Just for fun, on the side.
I can't imagine that the weight would be noticeably felt, but it is certainly measurable.
Hi Bastianna,

So, the extra +50 kg after refueling is very noticeable in the first fast corner, and it's costing me valuable seconds on my lap times.

A DTM car with an additional weight of 50 kg will not win any races anymore, and they have far more power than our TDI engines .

CU Gremlin.

Hello,

Could the fuel filter be clogged?

Before everyone starts shaking their heads, here's an explanation:
My Passat (96 kW, AVF engine) had a recurring problem for months: when accelerating, it would feel sluggish or even jerk. Initially, I attributed this to poor fuel quality, as it also occurred immediately after refueling (when the tank was almost empty and then filled), but this didn't seem conclusive compared to others who refueled there without any issues. Then, I searched for errors in the engine control unit using diagnostics, but ultimately found nothing until I replaced the fuel filter.
It was always peculiar that the problem would diminish or disappear as the amount of fuel in the tank decreased. Since I don't know the exact routing of the fuel lines, I can't yet explain this behavior, but I can assure you that this correlation must exist based on consistent observations.
Based purely on logical reasoning, I wouldn't have expected this connection, which is why I didn't change the filter until so late.

Best regards,
Ralf