How Much Power Does the Volkswagen TDI Lose in “Cheater” Mode?

Not all emissions tests are conducted with OBD2 link. In some relaxed regimes, OBD2 interrogation is the only component of the emissions test, and the car passes if the car determined there is no faults. I lived in a county with emissions testing and the OBD2 link was used as a pre-test before the dyno run, and to feed the VIN number into the state's computer to provide some assurance about the identity of the car being tested.

Some vehicles, like my Toyota, indeed behave slightly differently if there is a diagnosis computer connected. I don't know if this applies to the OBD2 link as well as the toyota-specific connector under the hood, but it's pointed out in the factory shop manual. At any rate this knowledge has prevented me from trying the "scangauge" type of data collection device.

It's the same basic chemistry. You've got O2+N2 (air) plus hydrocarbon (H-C=C-H sort of things) all mixed together and heated. Ideally all the 02 bonds with the H and C to form C02 and H20. If the mixture is lean and hot enough then there isn't enough H and C for all the O2 and it instead bonds with the N2 to form NOx.

The only real difference with the diesel is that the hydrocarbons are longer, which is why diesel is thicker and less volatile. Diesel needs to be hotter to break down these longer hydrocarbons and this is achieved via a higher compression ratio (14:1 instead of 10:1). That extra heat is an issue for N0x production if the mixture gets too lean. But if the mix is too rich, with not enough 02 for all the H and C, then you get incomplete combustion. That black soot is essentially just carbon that couldn't find any oxygen to bond with.

To avoid soot, so-called clean diesels run slightly lean and then rely on a catalytic converter to turn any N0x back into N2 and O2, but a dry cat can only go so far. BMW and others inject urea into the cat where it become ammonia (NH3). The O in the NOx grabs the H from the NH3 and the two Ns form N2. NOx + NH3 = N2 + H20.

The black stuff from diesels is soot, not smog. Soot is just unburnt carbon. The term 'smog' covers a whole manner of nasty chemicals, mostly oxides of nitrogen and sulfur.

Soot is relatively harmless compared to smog. A diesel producing soot is running rich and therefore is arguably cleaner than a "clean-diesel" running lean and pumping out oxides. Those carbon-belching trucks are far better for your lungs than the smoke-free VWs pumping out N0x. Beware the pollution you cannot see.

All of this testing can be seen as very poor, however, I would argue that we are running the wrong tests. Let me explain...

Imagine you were developing a car. As part of the project you would need to test, test, test and test the drivetrain and the engine. For your test data to be relevant you would want a controlled environment, e.g. car on perfectly flat road with no pot holes, turns or aerodynamic consideration. You could then adjust the variables and check the results - power, torque, emissions, noise level, oil use, fuel use, temperatures and so on.

In this development mode the test rig works pretty good. Figures can be produced that are important for the engine/drivetrain development. Variables can be changed and results measured. The figures - defeat device aside - are actually true with the normal margins for statistical measurement (not every engine will be 100% exactly the same even if it came off the same production batch).

The problem - defeat device aside - is when regulatory bodies use this data for what they need to know, i.e. real world performance. They accept data that they know is not real world and accept it as 'fact'.

If we look at our own testing for building apps, websites and such like we take a modular approach, testing our dev boxes with some type of 'seige' that does not factor in real world internet connectivity and bandwidth, not to mention how customers might use our products in the wild. We can even prove to our clients that their site isn't slow, sharing our metrics with them. Yet, in the real world things don't quite attain those metrics. Luckily nobody gets harmed if our 'squirrel picture app for cats' app falls short.

So, it is the procedures that are wrong and our standards bodies that are doing it wrong (by blindly accepting manufacturers' test data). We are lucky that VW have been cheating as we now are having the conversation about the testing methodology.

I have an idea for a different test method.

You take your cheating Volkswagen TDI without software fix to the local dragstrip on a day with little wind and do a series of test runs, you document your 1/4 mile time.

Then you send in your car for a fix to Volkswagen most likely a ECU software update as that is cheapest fix.

You retest your car at the drag racing strip, record the same number of runs.

If the numbers between the test run differ much you can sue Volkswagen as the car may have worse performance with the legal Nox emission software.

Here is a device that will let you test your car perfomance on normal roads. http://www.vboxmotorsport.co.uk/index.php/en/products/perfor...

Disclaimer I own a car with the affected engine.