AEM wideband readings

[9!'clipseDOHC]

This statement is incorrect.

I've actually been through this before. Even now, at idle, my WBO2 moves from about 15:1 to around 17:1 just sitting idle. Due to a trashed motor mount that I haven't had time to replace, the flex section in my down pipe is trashed and leaks. At idle, there is a low enough flow that a Venturi Effect is created at the flex section. This low pressure created by the flow of exhaust gasses causes air to be drawn into the exhaust. This is what is causing my lean condition at idle.

I went through it before, replaced the down pipe making no other changes and the AFR at idle returned to where it should be. So from first hand experience, it does happen.





You are correct, the point of a WBO2 is to view and possibly log AFR. The part you are missing is the way that we manipulate the AFR. For example, the SAFC removes airflow, thereby tricking the ECU into injecting less fuel. DSMLink actually drops injector flow resulting in a leaner AFR. The way you are describing lowering AFR involves turning up the boost. The problem is that since you aren't directly or indirectly manipulating fuel delivery, the only way that the AFR will change is when the system actually runs out of fuel.

The ECU contains 3 dimensional fuel and timing maps. Based on defined input parameters, it determines target timing and fuel delivery. What we do with tuning devices is manipulate or directly alter these maps to achieve a desired AFR.

Let's do an example and see if that helps. I'm going to make these numbers up since I don't have fuel delivery maps in front of me but you should still get the point.

Let's say that you are running 1.8g/rev of airflow and the ECU determines that an IDC of 86% is required to hit it's target AFR of 10:1. No matter what you do, without a tuning device or direct access to the ECU's maps, there is no way to change this AFR target and IDC. See where I'm going with this?

What you are saying is to increase boost, thereby increasing airflow until the AFR leans out. So let's turn up the boost and see what happens. With the boost bumped up 5psi, the ECU now sees an airflow of 2.4g/rev and determines that an IDC of 118% is require to hit it's target AFR of 9.5:1. The problem is that an IDC of 100%+ is impossible so the injectors are basically no all the time and injecting as much fuel as possible but actually needs more.

Since we now require more fuel than the system can supply, you'll see the AFR start to lean out. It's 100% the wrong way to tune because you're basically running the system past it's capacity in order to alter AFR.

It might look like it's working, but if anything changes, Boom! Bye, Bye motor.

See why this is a problem?

Thank you Mork and spyderturbo. I now understand what you are saying.

By the way Spyderturbo, my name is Nathan too.