MFA Performance Issues: A Quick Guide

Hi everyone,

Today, I drove a 1998(?) Passat station wagon with 81 kW (company car with over 130,000 km, engine code unknown) for about 300 km, with 4 people on board, mostly on the highway and country roads.

The engine felt very sluggish compared to my Golf (even without any modifications) (there was no opportunity for DZR attempts).

I kept wondering if it was only due to the extra weight + 3 people (empty weight according to the documents is 1,435 kg, G3 = 1,195 kg, and it's usually driven solo), or if something else wasn't right.

So, I observed the instantaneous fuel consumption at full throttle in 5th gear. The maximum value, between 2000 and 3000 rpm, was sometimes 13.3, sometimes 11.5, or somewhere in between. However, I couldn't actually feel the performance differences that would be expected based on those consumption values, which were roughly 15%.

I don't have the opportunity to do any data logging for the time being.

My wife's ALH-Ibiza consumes 11 liters under the same conditions, and this value has a much smaller variation compared to the Passat mentioned.
(My tractor, as a purist vehicle, of course, doesn't have any gimmicks like MFA, etc. )

My question to everyone:

What are the maximum instantaneous power consumption values you achieve (with the standard 81 kW motors) at full throttle in 5th gear, and how much do the values vary across multiple attempts during a drive?

Ideally, one should be able to identify a faulty or dirty mass airflow sensor (MAF sensor) based on this information, as it would then reduce the fuel injection amount, thus lowering the instantaneous fuel consumption.
But if fluctuations like those in the aforementioned Passat are considered normal, then one might be wasting their time with a "performance check" . . .

ulf wrote:

Hi everyone. ... My question to everyone: What are the maximum instantaneous power consumption values you achieve (with the standard 81 kW motors) at full throttle in 5th gear, and how much do the values vary across multiple attempts during a drive?

Hi Ulf,

1996 Passat 3A5 with AFN engine, original engine, approximately 135,000 km, according to the MFA's check mode, it displays approximately 0.7 liters less than the actual fuel level.
5th gear, full throttle - speed doesn't matter (between 50 and 200 km/h). Average fuel consumption: 12.2-12.4 liters, in 90% of cases 12.3 liters.

Best regards,
Munch.

Hi Ulf,

I don't think you can use MFA (fuel consumption) values for that purpose, because they are given in liters per 100 kilometers, not liters per hour. Also, you get all sorts of "noise" from factors like headwinds, tailwinds, etc., which affect the readings.

Normally, my motorcycle's average fuel consumption (ASV) at full throttle in 5th gear, while accelerating or near its maximum speed, is around 13 liters (usually around 12.5), but this can vary depending on the situation. For example, if there's a strong tailwind and the motorcycle is running near the upper end of the speed range, the consumption can be lower.

For example, I once drove on the A2 highway with a tailwind, using only about two-thirds of the accelerator pedal, and my speedometer showed 210 km/h. The display indicated just under 10 liters per 100 kilometers, which barely increased even when I used full throttle (although the speed only increased slightly, perhaps to 212 km/h).

Even under "normal" conditions, this impression is confirmed. Near the maximum speed (Vmax), the instantaneous fuel consumption decreases compared to acceleration, which makes sense because the distance traveled per unit of time (i.e., V) is significantly higher at maximum speed than during acceleration, while the fuel injection is already being reduced in that range (4400 or more RPM).

During my absolute maximum speed run (the speedometer showed just over 215, so realistically about 208), while driving on the A3 between Cologne and Frankfurt with moderate inclines, I couldn't look at the display... it was only for a short time, and I really just wanted to look at the road .

If you floor the accelerator at 70...80 km/h in 5th gear, the fuel consumption goes up to 12.5...13 liters, according to my opinion. I'll try it again tomorrow to get a more precise measurement and will post the results.

Best regards,

Jan.

Hello, mine has 127,000 km on it, and the MFA (Multi Function Display) indicates that it consumes 11.5 - 11.7 liters per 100 km when running at full throttle in 5th gear.

I don't think you can use MFA values for that purpose, because they are given in liters per 100 kilometers, not in liters per hour.

For models like the Passat 35i, Golf 3, etc., the MFA (Multifunction Display) can also display the current fuel consumption.

- Press and hold the MFA button (the one used to switch between displays).
- Ignition on.
- Ignition off.
- Ignition on.
- Start the engine.
- Release the button.


So, just like the trick with the odometer...
I cannot say whether the same method works for the 'newer' combination instrument panels (such as those found in Golf IV, Passat 3B, etc.) due to a lack of experience.

@ulf

I cannot provide you with current consumption figures. My 1Z didn't have any of that modern technology! But I can confirm that the Passat feels 'more powerful' compared to a similar Golf. I think this is partly due to the weight. My Passat, with a half-full tank and me in it, weighed around 1500 kg! The Golf weighs considerably less. And when you add extra passengers, you really notice every extra kilogram.

Hi Ulf,

Unfortunately, I don't have any values ready yet. However, I can talk about the vehicle's weight and inertia. I previously had the AFN engine in a Corrado (weighing 1190 kg) and now in an A6 (not yet weighed, but the registration says 1550 kg)... both received the exact same tuning maps in the chip. And the Audi feels much heavier. The mass airflow sensor (MAF) is also new. The first three gears work well, but after that, it feels surprisingly slow. 'Surprisingly' of course, compared to the Corrado. Perhaps the 18-inch wheels are contributing to the inertia/width, but that shouldn't be so decisive.

You could really feel the difference with four people in the Corrado. With three people, that's 210 kg – the Audi is definitely 400-500 kg heavier. That means you'd need three or even four more people (a total of 6-7 extra people) in the car to reach the weight of the Audi. I think that would have also robbed the Corrado of its dynamism, which the Audi currently lacks a bit.

Here's the translation:

That's a short story about weight .

Regards,
arne

'At full throttle, the display shows around 13.3 liters per 100 kilometers. At full throttle and maximum speed, it's closer to 11.9 liters. However, under normal driving conditions, the MFA (Multi Function Display) sometimes shows up to 30 liters, especially in the first and second gears, and around 17 liters in the third gear.'
When my LMM (likely referring to a Lambda sensor or Mass Air Flow sensor) was faulty, the fuel gauge only showed a maximum of 11 liters in 5th gear.
Regards,
windl

Jan6K wrote:

I don't think you can use MFA values for that purpose, because they are given in liters per 100 kilometers, not in liters per hour, and you get all sorts of "noise" effects like headwinds, tailwinds, etc., which affect the readings.

Hi Jan,

I believe that the instantaneous MFA (manifold absolute pressure) value can indeed be used to estimate the injection quantity per cycle.

Due to the well-known and "fixed" gear ratio, for example, in 5th gear, the number of engine revolutions per 100 km is clearly defined.
So, for example, if the instantaneous fuel consumption reads 12 liters per 100 km instead of 6 liters per 100 km, while in the same gear, it means that twice the amount of fuel is being injected per cycle.

And the smaller the gear, the more revolutions per 100 km, at which the maximum amount of fuel can be injected in each case.
Consequently, the instantaneous fuel consumption (L/100 km) is highest at full throttle between approximately 2000 and 3000 rpm in first gear, and lowest in fifth gear.

"Dirty" braking or drag effects probably don't play a role here, because when accelerating at full throttle, the engine (with the same RPM and sensor values!) should always receive the same amount of fuel injection, regardless of whether it's going downhill or uphill, for example.

Hi Ulf,

You are right about the acceleration; I need to revise my thinking on that.

By the way, I also took a look at the numbers today and even memorized them .

When accelerating from 80 km/h in 5th gear, my fuel consumption gauge goes up to about 12.4 liters per 100 kilometers and then slowly continues to increase until it reaches a maximum of 13.6 liters per 100 kilometers at approximately 140 km/h on the speedometer. After that, it decreases again. However, I had to stop at 150 km/h due to traffic – why do they always have to set up a construction site right there?

I believe I remember that it then goes upwards towards 12.

Best regards,

Jan.

windl wrote:

shows a value of 13.3 liters at full throttle. ... When my mass airflow sensor (MAF) was broken, the display only went up to a maximum of 11 liters in 5th gear.

Hi.

That's roughly what I was aiming for.

What surprises me about the company car (-> see previous post) is the fluctuation.
During the same trip, there was almost a 2-liter difference in fuel consumption between different full-throttle accelerations.

Charge air temperature differences should not have played a significant role: the airflow of at least 100 km/h should, in my opinion, quickly bring the charge air temperature (CAT) to a "static" relationship between the cooling air and the charge air .

Hi,

Reading what you all are saying about the weights for the Passat models makes me feel sick!
Ulf says that, according to the vehicle registration document, his company's Passat weighs 1435 kg.
Jörg says that his relatively new Passat weighs 1500 kg.

Here's the shocking part: according to the registration document, my Golf 4 weighs 1485 kg! When weighed (without the driver), it was 1415 kg, plus a standard driver weight of 75 kg, which equals 1490 kg!

As far as I can see, a Golf isn't significantly lighter than a Passat these days, is it? How much more "luxury weight" are we going to be forced to put in our cars (my Golf is a basic model, except for the air conditioning)?

With this type of consideration, one could probably assume that engines of equal strength a) consume more fuel and b) deliver worse acceleration values. Great progress .

Bertil wrote:

As far as I can see, a Golf isn't significantly lighter than a Passat these days, is it? How much extra weight are we going to be forced to put in our cars (my Golf is a basic model, except for the air conditioning)? With this type of comparison, it is likely that engines of equal strength a) consume more fuel and b) deliver worse acceleration values. Great progress .

Hi Bertil.

Let's just dream for a moment:

Ein robuster und starker 1,9er TDI (ob VP 37 oder PD sei mal egal . . .) in einem Golf 1 mit 8?? Kilogram empty.
Okay, let's say around 900 kilograms without airbags.

Can you imagine how many horsepower and what instantaneous fuel consumption "modern" cars would need to achieve in order to prevent the aforementioned dream car from driving circles around them ?

And how much (or rather, how little) fuel would a Golf 1 TDI consume under normal operating conditions?

Do you at least understand the signature below my posts?

I simply think that the "lightweight construction" slogan is just a way to placate car buyers and delay the arrival of the next generation (like the "tomorrow diet": I'll start tomorrow...).
And that the state actually likes to see large cars on the roads, because with every kilogram that is accelerated dozens of times every day, they guarantee a high fuel consumption, and thus substantial tax revenues.

Hi Ulf,

Hmm... maybe someone should strip down a Trabant chassis (the whole car weighs around 600 kilograms), install a 1.9 TDI engine as a central engine... and then see what happens.

Of course, the question also arises as to how much a TDI engine weighs on its own, regardless of any added weight.

Regarding the Ibiza, I have the feeling that it's significantly heavier in the front compared to the rear. In sharp braking situations, the rear wheels are likely unloaded to such an extent that they can hardly contribute to braking. This is evident in the wear patterns of the tires and brakes...

In the Polo 6N with the AEX gasoline engine (which, according to the specifications, weighed 200 kilograms less), using the handbrake to brake (right up to the point of locking) had a greater effect than in the Ibiza.

Does anyone know how much a 1.9 TDI engine weighs with its accessories?

A few days ago, in a review of the current V8 TDI engine in an Audi on Spiegel Online, the weight of this engine was mentioned as being around 270 kilograms... however, it wasn't specified whether this weight included or excluded any auxiliary components.

Best regards,

Jan.

Hi Ulf,

ulf wrote:

... Let's just dream for a moment: Ein robuster und starker 1,9er TDI (ob VP 37 oder PD sei mal egal . . .) in einem Golf 1 mit 8?? Kilogram empty. Okay, let's say around 900 kilograms without airbags.

... where can I buy it? ...

Quote:

Can you imagine how many horsepower and what instantaneous fuel consumption "modern" cars would need to achieve in order to prevent the aforementioned dream car from driving circles around them ?

Yes. You should take another look at my avatar... orange, ugly, light, and meanly fast (due to the rev limiter ).

Quote:

And how much (or rather, how little) fuel would a Golf 1 TDI consume under normal operating conditions?

Yes! I think around 1-2 liters would be possible.

Quote:

Do you at least understand the signature below my posts?

Yes! I was just trying to get people to think. In the Golf 3, it was possible to save a significant amount of weight by removing unnecessary features. With the Golf 4, that's almost impossible!

Quote:

I simply think that the "lightweight construction" slogan is just a way to placate car owners and delay the inevitable (like the "tomorrow diet": I'll start tomorrow...).

Good comparison .

Quote:

And that the state actually likes to see large cars on the roads, because with every kilogram that is accelerated dozens of times every day, they guarantee a high fuel consumption, and thus substantial tax revenues.

Of the manufacturers we produce for (and there are quite a few), it seems only BMW is currently interested in weight reduction (aluminum radio housings!). Even if we can only save around 500-1000g, it's a significant amount when considering all the components. The new 5 Series will be noticeably larger than the old one, but it will be 200kg lighter!

Jan6K wrote:

Does anyone know how much a 1.9 TDI engine weighs with its ancillary components?

According to information from VW, my 1Z model, including the transmission and auxiliary components, should weigh 173 kg.

Bertil wrote:

In the Golf3, it was possible to save a significant amount of weight by omitting unnecessary features. With the G4, this is almost impossible!

Hi Bertil.

For example, according to the catalog, the G4, with its 81 kW TDI engine, weighs 84 kilograms more than the G3 (in both cases, referring to the minimum curb weight).
Whether you choose the 3-door or the 4-door version, and whether it has air conditioning or not, the slight difference in weight is likely negligible.
Unless the list of optional extras for the 4-series is significantly shorter than for the 3-series, then it was actually possible to save more weight by omitting options from the 3-series than from the 4-series.

The heavier 4-door model, according to the catalog, accelerates from 0 to 100 km/h 0.2 seconds faster than the G3 with 81 kW... well, we've already discussed that before.

Quote:

It seems that only BMW, among the manufacturers for whom we produce (and there are quite a few), is currently interested in weight reduction (aluminum radio housings!!). Even if we can only save about 500-1000g, it's significant in the total of components. Although the new 5 Series will be noticeably larger than the old one, it will be 200kg lighter!

Oh, here's a start with one of those "innovative" manufacturers.
Then it could only take 50 years for VAG to follow the trend .

Does anyone here already know the curb weights of the Golf 5 compared to the Golf 4 with the same engine?