For anyone who has experience with emissions, here's a scenario (and its more academic than practical): A customer booked his car into the workshop for a test after a MOT failure in relation to emissions. I can chose any model but i think i will stick to a VW Passat 2.0, a 2002 model. It's a GASOLINE engine, compliant with the Euro4 emission standards, ignition and injections systems are functioning correctly, its consuming the recommended fuel and the engine is MECHANICALLY fine. The CO readings are high, 0.9% and the HCs are quite high as well at 550ppm. In my example, the catalytic converter has been partially melted as the cat worked too hard to keep up with the high emissions. Could someone outline a series of reason for the high levels of CO and HCs that led to the destruction of the cat? Upstream and downstream O2 sensors not working properly, coolant temperature sensor, etc...
I also pointed out that i had high levels of O2 due to a leak in an exhaust pipe before the upstream oxygen sensor. I'm looking for other components (mainly sensors) as the engine has to be mechanically fine and the ignition and injection system cannot be the problem.
Details about possible causes would be appreciated along with P codes that might come up as a result.
That is all relevant information in regard to emissions, but i have to stick to a few points. First of all, my example is just fictional: Of course it has to make sense. The engine has to be Mechanically fine, without any modifications. The ignition and injection systems are perfect as well.The cause of the problems has to be incorrect data coming from different sensors (like the oxygen sensors, upstream and downstream) or the coolant temperature sensor... or anything else that would lead to an incorrect fuel metering and would cause the engine to run rich.
The hole in the exhaust system affected to O2 value, rising the O2 value in the exhaust at 2.3% (therefore, the engine management ECU suspects that the engine is running lean and it is injecting more fuel in) - that lead to the catalytic converter failure and it damaged other sensors. I'm looking for these "other sensors" that could be damaged or that could affect the fuel metering, along with some P codes that might be generated.
Obviously any emission related problem would illuminate the MIL lamp and that's not a problem in my example. (there are actually some people who take their car to a MOT test with the MIL lamp on).
So I have to stick to a few points, where the engine is mechanically fine, and the fuel injection and ignition systems are ok... A flawed fuel metering has to be the problem caused by some sensors that could be responsible for that... This is what i'm basically looking for.
Relist: Incomplete answer. The answer is relevant to emissions, but it's not exactly what i'm looking for. This is only a hypothetical vehicle that i'm using in a project that i'm working on. All I need is a quick word of advice, and some faulty components that could affect the CAT (O2 sensors for example) and whats the most likely scenario in which the faulty O2 sensors would affect the fuel trim, therefore leading the CAT to work too hard. The fault doesn't have to appear in most cars out there, if it's possible to appear in one single car in the whole world that is meeting my guidelines (engine, injectors and ignition system in good working conditions) i'll be happy. Just something to make sense.
That's exactly the answer that I wanted!! Thanks for that Jake! I do appreciate a lot where you're coming from and I have a lot of respect for your vast experience and knowledge. The thing is that i'm working on a project and im approaching the deadline very quickly. I didnt read the task properly in the recent days and I had mechanical engine problems, I had to delete everything and look for an alternative. I kinda know where i'm going but i felt like i needed some guidance. The task is very clear in stating that: the engine is mechanically good and that there are no problems with the injection and the ignition system (my understanding is that that is ruling out dripping/leaking injectors, any misfires as they would be incorporated in the ignition system, and according to the task that cannot be the problem). Basically that's what i worked on and now i have to change the whole project. I have an air leak into the exhaust system upstream the oxygen sensor, which in my hypothetical example affected the lambda reading, making the engine management ECU to inject more fuel (therefore high HCs). I will say that the HCs also affected the upstream oxygen sensor and that partially melted the cat. What sort of HCs would u expect to melt the cat overtime (say maybe over a period of about a year) - and with the driver ignoring the MIL lamp. Just let me know if that makes sense to you, or if theres anything i should change.
On top of that I think you need a little bonus for your help.
Thanks a million for that Jake, you're a star!!