[ulises 335i]

you guys have been realy helpful ... But we need more time slips of the Turbo tuner. I would go to a drag strip but the closest one near me is a 2-3 hour drive .

[jon@themshop]

Originally Posted by Brisk

i thought the ecu controls AFR by retarding timing? isnt this true?
just asking

so how can the SSTT run lean? or other

The DME can control AFRs but controlling how long the injector stays open.

Let's not also forget that this is a direct injection system so now the DME can control fuel timing just like ignition timing and can control timing for the intake and exhaust camshafts depending on other inputs sensors like crank position, cam position, TPS, TMAP, etc.

[jon@themshop]

Originally Posted by Brisk

thanks for the reply Jon.. so wouldnt this mean that if the DME senses a lean mix, it would correct it?

and if it was really bad it would go into limp mode?

If the DME sees a lean AFR it will add more fuel by increasing injector on time. Not totally sure though if o2 sensors have an influence on fuel, cam, and ignition timing.

If it's really bad it may go into limp mode and set off a service engine soon light.

[sambonator]

Originally Posted by Brisk

i thought the ecu controls AFR by retarding timing? isnt this true?
just asking

so how can the SSTT run lean? or other

AFR (Air Fuel Ratio) is controlled by the ECU, by it increasing or decreasing the length of time the fuel injector remains open, which controls how much fuel is injected into the cylinders.

Rich AFR means more fuel mixed into a given volume of air. Lean means less fuel per volume of air.

"Timing" refers to the moment of time the spark plugs are fired, or the time when ignition of the air/fuel mix begins.

Aftermarket parts can cause a lean condition by either increasing the volume of air (increasing boost) or decreasing the input of fuel.

Since the SSTT increases boost, it can potentially cause a lean condition to occur (too much air, not enough fuel).

Hope this helps...

[sambonator]

If the oxygen sensors sense too much oxygen in the exhaust, it flags a lean condition. But I'm not sure how the ECU reacts to that... probably logs an error code, lights up the check engine light... because theoretically I don't think a stock engine with the stock mappings should ever reach a lean condition, unless there is a problem with the engine somewhere.