Unusual consumption

Hi!

Below, we discussed consumption. Personally, I'm not unhappy with my drinking habits because it's not that much. However, I can't save money!
"In the past, I always used to be in a huge rush to get to work (driving at full speed on the highway or encountering traffic jams, the same on country roads, and traffic in Frankfurt was always congested) - fuel consumption was 5.8 to a maximum of 6.0 liters. Now I have a different daily route, driving very calmly, only going straight, at speeds of 80 to 120 km/h, no city traffic, and still 5.8 liters. Just out of curiosity, I once drove a whole tank while focusing on saving fuel (always using 5th gear, idling downhill, etc.), and I got 5.7 liters. Now I'm driving more aggressively again - 5.8 liters!!! My fuel consumption absolutely doesn't change with my driving style." What is the reason for that?

A3 AHF 110 hp / Chip 140 hp, 140,000 km. Even without the chip, I experience the same behavior. It used to be 5.4 liters...

Best regards,
Uwe

Uwe wrote:

I was just curious, so I once drove an entire tankful of gas while trying to save fuel (always using the 5th gear, coasting in neutral downhill, etc.), and I got 5.7 liters. Now I'm driving normally again - 5.8 liters!!! My fuel consumption absolutely doesn't change with my driving style. What is the reason for that?

Hi Uwe,

Here are a few notes that might help explain part of the puzzle:

Driving slower only makes a difference if you don't automatically downshift at the same time.

Driving downhill in neutral is not the most fuel-efficient option because the engine still consumes fuel at idle speed.
Coasting downhill without using the accelerator activates the coasting function (as long as the engine is running above 900 rpm) --> only then is the fuel consumption actually zero. Or when the engine is turned off.

When refueling, the fuel nozzle can shut off significantly earlier or later depending on the car's incline, splashing or foaming diesel, etc., and this can easily result in several liters of difference.
Let's calculate.
50 liters of fuel added after 1000 km driven = 5.0 liters per 100 km fuel consumption.
With a little more patience, I managed to fill the tank with 52 liters, which seems like 5.2 liters based on the display.

These inaccuracies tend to even out somewhat after multiple fill-ups with the same driving style.

Hi,

It is certainly important that:
- Use VERY, VERY, VERY little gas.
- Shift up early, when the engine speed is below 2,000 RPM.

I once managed to go for about 100 km.
I was rewarded for that with a fuel consumption of 3.7 liters per 100 kilometers!
And there were also 2 cold starts included!
Normally, my fuel consumption (or rather, my car's fuel consumption) is 5.4 liters per 100 kilometers.
It was interesting, once. While driving on the highway, I let myself be 'drafted' by trucks at a speed of 90 km/h.

Markus H. wrote:

What is definitely important is: - Use VERY, VERY, VERY little gas. - SHIFT UP, SHIFT UP, SHIFT UP very, very, very early.

Hi.

That's right... and equally important is: let it rest, let it rest, and let it rest again.
That means, take your foot off the gas pedal as soon as it might be possible for the car in front to slow down. And maintain a safe distance to be able to "absorb" the common accordion-like driving pattern of car convoys consisting of more than 3 vehicles (where the last car follows a pattern of gas-brake-gas-brake...).

Note: Those who have to brake in predictable traffic situations have likely accelerated too much beforehand, thereby wasting fuel.

Markus H. wrote:

... It is certainly important that: - Use VERY, VERY, VERY little gas. - Shift up early, when the engine speed is below 2,000 RPM. ...

Hi,

not quite right...
Modern engines are designed to achieve optimal efficiency just before reaching full load. Therefore, it's not a problem to accelerate quickly to the desired speed and then let the car roll along at a relatively constant speed (as Markus says: "use VERY, VERY, VERY little throttle"). This saves fuel in the long run compared to slowly accelerating to the desired speed. To maintain momentum through curves and avoid excessive braking (as Ulf mentioned), even with sporty driving, a very low fuel consumption is possible.
The best fuel-saving tip for all engines is: always stay within the engine speed range around the maximum torque (for a TDI, that's around 2000 RPM).

Hi!

I had already incorporated all of these tips into my driving style. So, after starting (I live in a tiny village in the Taunus mountains), I quickly shift into 5th gear and then drive up a slight hill at about 80 to 90 km/h. On the other side, I briefly accelerate to 120 km/h (still in 5th gear) and then put the car in neutral. On one of my fuel-saving trips, I turned off the engine for 4 km. At the end of the hill is my workplace, with no city or town traffic. I drive past the town sign at a constant speed of 60 km/h and roll almost to a complete stop without braking, almost reaching my destination. In the afternoon, I repeat the same process in the opposite direction. The distance is simply 16 kilometers. I did this for 1,000 kilometers / 6 weeks. I've had enough of this! However, I can't really drive any differently because of the route. I always fill up at the same pump at the only gas station in the area, and I always fill it right to the top. Consumption: 5.7 liters!

"Previously, I had to drive over 80 kilometers to Frankfurt. The first 25 kilometers were on a relatively open, secondary road. After a gentle warm-up, I really put my foot down. Then, there were 50 kilometers of congested or completely free (between the traffic jams) autobahn, with speeds ranging up to 200 km/h (or 0-40 km/h in traffic jams), followed by another 5 kilometers of city traffic (about 20 minutes)." The return journey was in the reverse order.
Consumption: 5.9 to 6 liters.

Conclusion: It's not much, but it won't be significantly more even with a more economical driving style. Thank you for the answers. I don't think the correct explanation is among them. Does anyone know of another possible cause?

Best regards,
Uwe

Hi,

But if you have a cold start for every 16 km, doesn't that significantly increase the fuel consumption?
On the way to Frankfurt, you end up driving a much longer distance. Perhaps the less frequent cold starts compensated for the faster driving style to some extent. Could it be?

Sure, I can do that. Please provide the text you would like me to translate from German to English. I will provide two different translations, if you prefer.
Perform the following with the engine fully warmed up and the tank filled.
Then, carefully drive a defined route once, and then drive the same route again, but faster. Every time you fill up the tank, calculate the fuel consumption.
The distance should be at least 100 km.
(Otherwise, the people at the gas station will get really upset if you try to pay for just 0.7 liters of diesel...)


P.S.:
This question might be a bit too simple, but still:
How do you obtain the average consumption?
Through the onboard computer?
Or did you calculate it yourself, or did you use a calculator?
If it's the on-board computer, it could, of course, be functioning very inaccurately.

Bertil wrote:

The best fuel-saving tip for all engines is: Always stay within the RPM range around the maximum torque (for a TDI, that's around 2000 RPM).

Hi Bertil,

I wouldn't say that in general, because of the following consideration:

Imagine taking the spark plugs out of the engine (so that the compression is gone) and then turning the engine over by hand for 15 revolutions. It's going to be tough, right? Although you only had to overcome the internal friction.

Therefore, if you drive at 2000 rpm instead of, for example, 1300 rpm, approximately 1.5 times the work must be done per meter to overcome engine friction (compare this to the engine braking effect in a high or low gear).

It's my opinion that the engine cannot be that much less efficient running at 1300 RPM instead of 2000 RPM, such that the frictional savings would be "overcompensated."

I'm not afraid to let the engine idle at 1200 rpm. I only shift down if the acceleration in the higher gear isn't sufficient.
And my average consumption over 5 years in this area, which is 4.2 liters, seems to confirm that .

Hi!

Markus H. wrote:

But if you have a cold start for every 16 km, doesn't that significantly increase the fuel consumption? On the way to Frankfurt, you're covering a much longer distance. Perhaps the less frequent cold starts somewhat compensate for the faster driving style. Could it be?

Possible. "How much does a cold start cost?"

Markus H. wrote:

How do you obtain the average consumption? Through the onboard computer? Or did you calculate it yourself, or did you use a calculator?

Unfortunately, I don't have an MFA (Multi-Factor Authentication) device available, so I had to use a calculator after driving over 1,100 km.

Best regards,
Uwe

Hi Ulf,

"I always keep the engine speed slightly above the maximum torque, not below (to have some reserve power)." The (free) torque curve includes the motor's internal friction, and then it should be correct (I think, but your approach gives me something to think about...).
However, I need to find a compromise between "a crocheted toilet paper roll on the dashboard" and "Walter Röhrl." My driving route is extremely winding and hilly, and with an average fuel consumption of 5.8 liters (including trips with the caravan) over the past three years, I think I'm doing pretty well. "When I put the toilet paper roll on the shelf above the dashboard or when I'm on long highway drives, I also get fuel consumption of less than 5 liters per 100 kilometers."

P.S.: My rallye Jetta also has a crocheted toilet paper roll attached to the shelf above the dashboard (seriously!!), but it doesn't move around much. I can't seem to resist adding more fuel (currently using 10-12 liters of regular gasoline with an octane booster).

Hi Bertil,

In the torque curve, the engine friction has already been subtracted, so it doesn't provide any information about the engine's fuel efficiency or overall efficiency.

However, your approach is not fundamentally wrong: the specific fuel consumption of the industrial TDI (AFD with 60 kW; unfortunately, I don't have other diagrams) is lowest between 1700 and 2200 rpm (approximately 208 grams per kWh).
Below 1700 rpm, it increases "steeply" and ranges between 1100 and 1400 rpm at 228 g/kWh – which is a full 10% worse than in your preferred speed range.
This value is likely determined under full load conditions to establish a defined operating point.

On the other hand, the acceleration and deceleration forces acting on all the oscillating masses (pistons, connecting rods, valves) increase quadratically with the engine speed, which correspondingly increases the pressure on the bearings (and thus the friction). Therefore, to compensate for the increased internal friction at 2000 rpm, it is definitely not possible to use the same amount of diesel as at idle (approximately 8 mg per revolution).
According to this, the friction losses caused by the engine (per distance traveled) are likely to be higher at 2000 rpm compared to 1100 rpm (an example for 50 km/h in 3rd or 5th gear). The number of people walking (or the number of pedestrians) has more than doubled.

Balance sheet of this arbitrary and superficial examination:
At 2000 rpm, the engine (under full load) operates approximately 10% more efficiently than at 1100 rpm, but its internal frictional losses constantly consume at least 100% more energy per meter traveled.

So, I continue driving through the area in the highest possible gear, only downshifting when the available acceleration isn't sufficient. While the torque build-up in the low RPM range is slightly better with a VTG turbocharger compared to a wastegate, I would essentially drive a 1Z engine the same way, and probably just shift down a bit more often as a result.

Besides, I can achieve the same speed with fewer engine revolutions per mile, and each revolution contributes to the overall wear and tear.

Hi Ulf,

ulf wrote:

... However, your approach is not fundamentally wrong: the specific fuel consumption of the industrial TDI (AFD with 60 kW; unfortunately, I don't have other diagrams) is lowest between 1700 and 2200 rpm (approximately 208 grams per kWh).

That's exactly the area I always work in. The 1Z engine achieves its maximum torque at 1900 RPM!

Quote:

Above 1700 rpm, it increases "steeply" and reaches 228 g/kWh between 1100 and 1400 rpm – which is a full 10% worse than in your preferred speed range.

Sure, here's the translation:

"S.O." translates to "Single Origin" in English. It refers to coffee beans that are sourced from a single farm, region, or cooperative. This allows for greater traceability and quality control, as the beans can be more easily tracked back to their origin.

Quote:

This value is likely determined under full load conditions to establish a defined operating point.

Yes.

Quote:

On the other hand, the acceleration and deceleration forces acting on all the oscillating masses (pistons, connecting rods, valves) increase quadratically with the engine speed, which correspondingly increases the pressure on the bearings (and thus the friction). Therefore, to compensate for the increased internal friction at 2000 rpm, it is definitely not possible to use the same amount of diesel as at idle (approximately 8 mg per revolution).

Sure, it's correct, but we all want to move forward, don't we?

Quote:

According to this, the friction losses caused by the engine (per distance traveled) are likely to be higher at 2000 rpm compared to 1100 rpm (an example for 50 km/h in 3rd or 5th gear). The number of people walking (or the number of pedestrians) has more than doubled. Balance sheet of this arbitrary and superficial examination: At 2000 rpm, the engine (under full load) operates approximately 10% more efficiently than at 1100 rpm, but its internal frictional losses constantly consume at least 100% more energy per meter traveled.

So, it seems we're still talking about maximum torque...

Quote:

So, I continue driving through the area in the highest possible gear, only downshifting when the available acceleration isn't sufficient. While the torque build-up in the low RPM range is slightly better with a VTG turbocharger compared to a wastegate, I would essentially drive a 1Z engine the same way, and probably just shift down a bit more often as a result.

"...so you drive pretty much like me. The 1Z isn't really fun to drive below 1400 RPM..." The torque on the 1Z engine feels a bit more abrupt compared to the VTG engine (my brother has one). However, the 1Z engine becomes sluggish like chewing gum from 3000 RPM, which the VTG engine does not.


BTW: Can you explain one of the effects of a VTG engine to me?
"When I'm driving uphill with a VTG engine and a trailer attached, and I briefly lift off the accelerator (less than 1 second), it takes a very long time to regain power. The 1Z engine immediately returns to its previous power level. Is the VTG perhaps a bit sluggish?" I have observed this effect in two new cars (a defect is highly unlikely).

But if you have a cold start for every 16 km, doesn't that also significantly increase the fuel consumption, or not?


I drive 12 km to work. The fuel consumption is 4.8 - 5.3 liters. FROM work 5.6 - 6.0 liters.
(going uphill). Speed approximately 110 km/h, even when going uphill

Octavia station wagon, 66kW (ALH) engine, automatic transmission.

A cold start doesn't really matter that much with a TDI. After all, the fuel doesn't have to pass through a very long intake manifold and then be compressed. Deposits on the cylinder walls are probably less likely to occur, which is something you want to avoid with a direct injection system .

Be careful when observing the MFA (Multifunction Display) while the engine is idling. The displayed value is somewhat influenced by the alternator's afterglow.

CU Gremlin.

Bertil wrote:

BTW: Can you explain one of the effects of a VTG engine to me? "When I'm driving uphill with a VTG engine and a trailer attached, and I briefly lift off the accelerator (less than 1 second), it takes a very long time to regain power. The 1Z engine immediately returns to its previous power level. Is the VTG perhaps a bit sluggish?" I have observed this effect with two new cars (defect almost ruled out).

Hi Bertil,

The fundamental differences between wastegate and VTG turbochargers, in my opinion, do not explain this. As long as the VTG (Variable Turbine Geometry) is set to its maximum pressure setting, the pressure should increase at least as quickly as it would with a wastegate turbocharger.
Perhaps there's a small catch here: above approximately 1400 rpm, the variable turbine geometry (VTG) starts to move slightly away from its maximum position during partial load and boost operation, while the wastegate remains completely closed.
If then a large amount of force is required in the main passage, the VTG must first be set to its maximum level again, which takes approximately 1/3 of a second - as long as nothing is jammed .

I also experience a similar difference between my wife's ALH Ibiza and my AFN, even though both have VTG turbochargers.
"However, the ALH was manufactured in 2001, making it 4 years younger than mine, and it responds much more conservatively to the accelerator pedal, even if you disregard the difference in power output." The difference in torque isn't that significant: 235 Nm versus 210 Nm is only a 12% difference.

I suspect that the newer TDIs are slightly throttled in terms of immediate acceleration so that boost pressure can build up first before the fuel pump is fully engaged --> this is to reduce soot emissions.

Hello!



Take a look at this. That's really interesting.
Consumption characteristics can be found, for example, in Figure 5. Instead of thinking about the applied mean pressure, you can also consider the torque.
Best regards,
Ernst.http://www.uni-magdeburg.de/MWJ/MWJ2001/tschoeke.pdf{MARKER}

Hi everyone,

I also have a G4 ALH with 66kW. I installed an LDA (Linear Dosing Adapter) but I'm also having the problem of poor boost control. When I accelerate, the boost pressure shoots up to almost 1.4 bar and then drops suddenly to 0.5 bar after about 1-1.5 seconds. This noticeably reduces the power. It then takes several seconds for the boost pressure to rise again to 0.85 bar.
'I took the car to the workshop last Monday to have the problem investigated. The VW master technician also said that something wasn't right. He then replaced the fuel filter because it was drawing in air. However, that apparently only made a minimal difference. The VTG mechanism is supposedly working smoothly. The VAG diagnostic tool, which was used for the measurement, apparently only takes a snapshot at 3000 RPM. And supposedly, the boost pressure is okay at that RPM. However, I can still only achieve a boost pressure of 0.5 bar at full throttle, even at that RPM. The technician now wants to obtain approval from VW to replace the turbocharger.' To this day, I haven't received any feedback.
The car has already frustrated me several times at the beginning, when I tried to overtake and then nothing happened, forcing me to abort the maneuver.
However, there is a small way to get the most out of the 'full' acceleration: Only give it enough gas so that the boost pressure remains below 1 bar, and then slowly increase the gas pedal pressure .

Regards,

Eike.