MBC and our MS3 ECU...

[tru-boost]

the car uses the MAF to determine how much fuel to add. it will still be getting proper readings and will maintain a stock like A/F .

 

[mghunt]

the car uses the MAF to determine how much fuel to add. it will still be getting proper readings and will maintain a stock like A/F .

This is only true if the injectors, the maximum injector duty cycle, and the fuel pressure can support it. In other words, the fuel maps in the ECU have to be able to support the added air. It is completely vehicle dependent. Some vehicles are more "tunable" than others.

My previous car had an injector duty cycle limitation. Basically the fuel maps were designed with the factory equipment in mind. If the turbo was replaced, than boost could be maintained at higher engine RPMs. However, the fuel system couldn't support the higher boost in this RPM range. The duty cycle limitation would eventually lead to the ECU trimming out the extra fuel when it was in closed-loop operation.

I don't think this is an issue with the MS3, but the reason I suggest keeping an eye on fuel trims and a/f ratios when you turn up the boost.

 

[laloosh]

Only if the injectors, the maximum injector duty cycle, and the fuel pressure can support it. In other words, the fuel maps in the ECU have to be able to support the added air.

My previous car had an injector duty cycle limitation. If the fuel pressure was adjusted for maximum boost during open loop operation, then the engine pulled fuel back at idle. In other words, no matter what was done to the fuel pressure, the motor would end up pulling fuel to stabilize the idle and would starve the engine of fuel at high RPM/boost conditions.

I don't think this is an issue with the MS3, but the reason I suggest keeping an eye on fuel trims and a/f ratios when you turn up the boost.

from what i read on here our injector duty cycles are nowhere near being a limitation.

 

[fourthmeal]

The bottleneck is all about the mechanical fuel pump on the engine block.

 

[mghunt]

from what i read on here our injector duty cycles are nowhere near being a limitation.

Good to know.

 

[nig3]

Stupid question. If your computer thinks your spooling 15.6psi but your really spooling 18-20 psi, how does that give you power, wouldnt you need more fuel, and your computer not know it needs to give it to the car?

yeah hes kinda retarded, the mbc actually bleed presure off to the wastgate not the map sensor.

 

[laloosh]

yeah hes kinda retarded, the mbc actually bleed presure off to the wastgate not the map sensor.

um no, the atp fcd defender bleeds pressure off the map

 

[mghunt]

Simply put, the "defender" is a pressure regulator. It "caps" the pressure so it doesn't exceed a set level. So, the car's ECU is happy because it doesn't see boost pressures that are too high.

jhowey, to actually answer your question, If we boost above the ECU's limit, yes, we need to add more fuel. However, the ECU will know how much fuel to add based on the mass airflow sensor (MAFs) readings. It is able to compensate, within reason.