Air Mass Sensor: The Story Behind It

Once upon a time, a clever mind realized that the development of fuel mixture preparation hadn't reached its end with the traditional carburetor. So, he devised a relatively simple mechanical fuel injection system that was also used in relatively inexpensive vehicles, such as the Volkswagen Golf I GTI. This injection system was quite reliable and, apart from the price, was significantly superior to the carburetor. This system was called K-Jetronic and was produced by Bosch. The amount of fuel injected was controlled by a valve in the engine's intake air stream, which acted upon a flap.

Then came the catalytic converters, and to ensure they worked effectively at a Lambda value of 1, the K-Jetronic was supplemented with an electronic actuator. This also worked quite reliably. However, the next stage of development was already emerging. There were electronic fuel injectors that were controlled by an engine control unit. The signal for this came again from a valve in the intake air stream, which now actuated a potentiometer. This system, called L-Jetronic, also worked extremely reliably, much to the delight of our valued customers.

"Forget about mechanics," thought another ingenious mind, and suddenly, the hot-wire air mass meter was born. A wire in the intake air stream cooled down depending on the amount of air flowing past, and that provided the crucial signal for the fuel injection quantity. Now, even the temperature sensor of the L-Jetronik could be eliminated, because temperature fluctuations also affected the output signal of the hot wire. And once again, the system worked, and customers were thrilled, provided they were familiar with the fuel injection system and realized how cleverly designed and yet remarkably reliable it was.

A dark day dawned when someone pondered how to optimize workshop profits and boost the sales of mass airflow sensors to unprecedented levels. From this nefarious idea came the hot-wire mass airflow sensor. This device caused the strangest engine problems, was even installed in diesel engines, and drove hordes of frustrated customers to authorized workshops and Bosch service centers. Despite increasingly sophisticated on-board diagnostics, the defective hot-wire MAF sensor was often difficult to identify as the cause of the problem. Workshops experienced a surge in business, automotive technicians could feel important using computer diagnostics, and the sales of poorly designed MAF sensors skyrocketed.

And the moral of the story? People, I am REALLY ANGRY!

mcgregg

Hi McGregg,

The problem is: you haven't understood the overall concept.

Think about it. In the past, when something broke, it was usually obvious, and that's why it was replaced. (For example, a contact breaker or a throttle cable...)
There were also a lot of things that needed to be replaced regularly, often quite frequently. (Spark plugs, oil, air filter, all every 7,500 kilometers.)
The workshops were busy, and the workers were happy and satisfied. Those who could repair tractors could also work on cars, and vice versa, as long as they had the strength and knowledge.
It was electrically powered, the horn served as the ignition, and that was it.

'Nowadays: Oil often only needs to be changed every 30,000 kilometers, spark plugs last forever, and transmission fluids are no longer changed. (In order to still sell a few automatic transmissions, the oil is no longer changed in them either.)'
And the absurdity: To prevent customers from changing the oil themselves, Audi stubbornly refuses to disclose the type of oil and the amount required!

Today, things break that still look brand new (like mass airflow sensors), and no one knows for sure if they're actually broken, especially the person who's replacing them.
(See eBay: brand new turbocharger, ESP, control unit, cheap...)
A mid-range car has hundreds of times more computing power than what the Americans had available for the Apollo program. And this is often maintained by people who learned their trade working on vehicles like a 240 diesel, a Renault R4, or something similar.

'I wonder how happy they are when parts need to be replaced before they can even start properly addressing the problem?'
(e.g., a post on this forum stating that a mass airflow sensor was replaced instead of the air filter...)
If, after many invoices, the customer still hasn't been helped, they'll just go to another workshop, and you'll be rid of the problem and the complaining customer.
They cannot live with systems that are constantly becoming more reliable.
So, some well-known issues are simply being ignored, especially when it comes to parts that:

Affordable options (approx. €25) include:
Easy to change. However, at least 1 working hour must be recorded (using a so-called mixed calculation).
And most importantly: Not available for purchase through regular retail channels. That way, we could dictate the prices.

Ideal for things like: LMM, ESD.

Or, you can create a lot of unnecessary work and design the timing belt housing in such a way that you can't even access it on the A4 model until you've spent an hour working on it. And then, maintain this system of creating extra work throughout the entire production run of the model.

Imagine those three worst, long-known TDI problems simply disappeared, and it would be a super reliable car. But who, besides the customer, wants that?

And before anyone comes along and says: 'My BMW, Mercedes, Korean car, Japanese car, etc. is better.'
The entire automotive industry operates this way.

@mcgregg

Well... my old 1.3S had 75 horsepower and consumed 13 liters of gasoline.

The 2.0i had 115 horsepower and consumed 10 liters of fuel.

The 1.8T engine has 150 horsepower and consumes 9 liters per 100 kilometers under the same driving conditions.


That's all there is to say about carburetors, throttle valve air mass meters, and hot-film mass flow meters, and the technologies that have evolved alongside them...

Nowadays, there are no more burnt-out breaker contacts, no blown capacitors, no clogged carburetor jets, or rotten seals (which are present in multiple places in the carburetor).

'Those classic old cars' are still here every day in the workshop, and they break down just as often as the modern ones. The types of problems they have are just different.
Garth already understood the concept.
In the early days, the ignition modules would often fail, or the distributor rotors would break, until we got the production process under control.

By the way, you haven't quite grasped the principle of the Hot-Film Mass Flow Meter (HFM). The flow control valve and hot wire only measure constant airflow with sufficient accuracy. The HFM is so fast that it can detect pulsating airflow, and thanks to the structure of the sensor layer, it can even determine the direction of the flow. This is particularly important for fuel injectors, as it allows for even further reductions in fuel consumption because the lambda calculation becomes more accurate and, above all, significantly faster.

CU Gremlin.

garth.brooks wrote:

So, some well-known problems are simply ignored, especially when it comes to parts that: It is inexpensive to buy (approximate monthly cost: €25)

.
Hi Garth,

Do you have this insider information from a reliable source?

Then a profit margin of around 900% would really be outrageous, and perhaps something that should be brought to the attention of publications like Auto Bild, etc.

Hello Ulf,

My personal estimate is around 30€. For simple injection-molded parts, the profit margins can be much larger. If you know the material cost and estimate the tooling costs, it's quite easy to determine the part cost.

Der Irrsinn geht aber noch viel weiter. Die Autohersteller haben meist mit den Zulieferern Verträge, die eine Gewährleistung für Teile von über 10Jahren vorsehen. Jedes defekte Teil muß vom Zulieferer oft für mehr als dessen Verkaufspreis in dem oben angegebenen Zeitraum zurückgenommen werden. Der Automobilhersteller verdient also mehrfach an jedem defekten Teil, das den Weg von der Werkstatt zurück zum Hersteller findet. Der Kunde bezahlt nach seiner kurzen Gewährleistungfrist mit 3-20x und vom Zulieferer gibt es nochmal 1-3x. Also doch kein schlechtes Geschäft. Warum die Zuverlässigkeit erhöhen wenn man soviel Geld an Standarddefekten verdienen kann. Nach Übersee (Japan) ist die Ersatzteilrücklieferung nicht so lohnend. Daher ist es für die Japaner billiger, zuverlässigere Autos zu bauen. Alles Sure?

Best regards,
Christian.

ulf wrote:

garth.brooks wrote: So are some well-known problems simply ignored, especially when it comes to parts that: You can buy them cheaply (approx. 25€ per unit) . Hi Garth, Do you have this insider information from a reliable source? Then a profit margin of around 900% would really be outrageous, and perhaps something that should be passed on to Autobild or a similar publication.

chris11 wrote:

Automobile manufacturers usually have contracts with their suppliers that provide a warranty for parts lasting more than 10 years. Each defective part often has to be taken back by the supplier for more than its selling price within the period specified above.

Hi Christian,

However, in the case of LMM (likely referring to Lambda Measuring Module), this should be an incentive for Bosch to further develop these components, so that they don't have to take back every(?) part they supply to the VAG group after a maximum of 100,000 km of mileage.

Because, in my opinion, there must be at least thousands of withdrawals per year?

It's roughly twenty times more expensive during the warranty period, which is why defective parts that are essentially worthless have to be returned to the car manufacturer. (Two years is common, but not always for all parts; usually only for the more expensive ones – a mass airflow sensor might even be included. 10 years is definitely not the standard!)

Let's calculate: If you have approximately 10% in your pricing calculation for a product, but you pay 20 times the price for every failure within the first 2 years, then you are already losing money with a failure rate of just 0.5%.

This creates a level of complexity that is only comparable to space travel and that already exceeds the capabilities of the MIL standard.

I'm not comfortable with that statement about the Japanese - There's a simple trick to increase the reliability of your vehicles when traveling abroad:

'Each new model is initially only sold domestically for the first six months, and then exported. By that time, the most significant flaws have been identified and corrected. The Japanese are masters of this, and as anyone can see, especially in the field of consumer electronics, new Japanese technologies are always first released in Japan, and much later in the US/Europe.'


And: The tests conducted by ADAC only cover vehicles up to approximately 7 years old.
There are statistics that show that the situation rapidly deteriorates for Japanese people as they get older.

Deleted upon request.

However, that should be an incentive for Bosch to continue developing these components, so that they don't have to take back every(?) part they supply to VAG after a maximum of 100,000 km of mileage?

That's not due to Bosch when it comes to LMM (lambda sensors), but rather to the car manufacturers.

because they have completely disregarded Bosch's installation guidelines in some cases...

keyword: ingested spray ...

Sure, here is the translation of the text from German to English:

'Cu Gremlin'

In order to sell a few more automatic transmissions, the oil is no longer being changed in them anymore.
And the frustrating part: Audi stubbornly refuses to disclose the type of oil and the amount needed, presumably to prevent customers from changing it themselves.


What do you do when the transmission needs to be rebuilt and therefore new oil needs to be added? Also, isn't an oil change still the first step to take when you have problems with the automatic transmission?

Hi,
"Yesterday, I had a copy of the operating manual for a 307D model manufactured in 1986. In addition to the usual information, it mentioned some unusual maintenance intervals, such as changing the coolant every 3 years, the coolant hoses every 6 years, and servicing the power steering every 300,000 kilometers."
A 307 isn't a great car, but those specific parts should have been state-of-the-art, although apparently they never needed to be replaced anywhere else.