Has anyone ever seen anything like this? Evo7, if it matters. On this log the load value drops by 100 in an instant, resulting in massive knock. I am assuming this is a MAF error. You can see that the airflow Hz drops considerably, however I assume there was no actual reduction in airflow, hence the ECU looked up timing values too high for the current airflow and calculated fuel pulse width values that were too low. Unfortunately, due to an error with Evoscan logging the wideband, I wasn't able to log AFR. If I were able to, I would be able to confirm that the airflow didn't actually drop, since the AFR would go instantly lean.

I am wondering if there is anything physical, other than a MAF error that could cause this. I can't think of anything. Air would have to be bypassing the MAF, but any sort of boost leak would result in the engine getting less air than reported by the MAF, not more. However, it is kind of weird that the MAF would have a momentary glitch like this.

There is some oil in the engine bay, so this incident has likely resulted in damaged ring lands.

 

Yes - I've seen similar momentary MAF glitches and had to replace it to fix this twice in 250k miles.

 

OK, thanks. Previously, I was expecting if a MAF fails it would fail completely. I think I will recommend the owner switches to SD.

 

It sounds like you're experiencing a significant drop in load value and knock on your Evo 7, potentially due to a MAF (Mass Air Flow) error. Your analysis of the situation seems logical, where a sudden drop in airflow frequency without an actual reduction in airflow could lead to incorrect timing and fuel calculations by the ECU, resulting in knock.

In this case, a malfunctioning MAF sensor could be a possible cause. It's responsible for measuring the incoming air mass, and if it provides inaccurate readings or experiences a glitch, it can affect the engine's performance and calculations. Checking the MAF sensor and its wiring for any issues, such as contamination, damage, or loose connections, could help determine if it's the source of the problem.

While boost leaks typically result in reduced airflow, it's worth checking the intake system and intercooler connections for any potential leaks or loose clamps that might allow additional air to bypass the MAF sensor. Even a small leak can affect the accuracy of the MAF readings and lead to incorrect fueling and timing.

Regarding the presence of oil in the engine bay, it's essential to investigate and address any oil leaks. Oil contamination can affect the engine's performance and potentially cause damage to various components, including the piston ring lands. Ensuring a proper seal and resolving any oil leaks is crucial for maintaining the engine's health and preventing further issues.

However, it's important to note that without proper diagnostic tools and thorough inspection, it can be challenging to pinpoint the exact cause of the problem. To get a more accurate assessment and identify potential issues, it's advisable to consult with a qualified mechanic or tuner who has experience with Evo 7s and can perform a comprehensive diagnosis.

Addressing the issue promptly and resolving any underlying problems will help ensure the optimal performance and longevity of your vehicle.