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Posted by Drew in Houston [Email] (more from Drew in Houston) on Mon, 13 Dec 2004 14:08:19 Share Post by Email
In Reply to: One more for the MAF, Vigge, Mon, 13 Dec 2004 12:45:43
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Now I know what you're saying--basically that the original "setpoint" after adaption won't be zeroed and centered in relation to the total system response capabilities. So additional head-room won't be there for further adaption.

That I can easily accept and we agree upon. :)

However, what I'm trying to communicate is that from my experience with my single T7 car I'd say that dosen't necessarily cause a system controls problem. In my case, the VE has been improved, the MAF sensor knows that because of increased throughput and tells the ECU, the programming adds fuel through adaption, and everything is fine--because the extra throughput is within the programmed limits of the adaption adder. And I have to think that I'm very very near to the limits of that adaption ability. And that may not be the same in your case in running greater displacement. Now I understand that it's that adder that you're saying will cause a problem and need to be re-zeroed in relation to system total flow adaption.

To mechanically lower that adder I'm planning to up the fuel rail pressure a little with a VFPR and a good gauge (not a real good thing for the injectors or the pump, I know) to provide more fuel per injection cycle to get some of that adaption headroom back. Which will work, because T7 has no way to determine the actual fuel flow rate. It doesn't know the flow rate because there isn't a direct flow metering sensor-- ie, fuel load metering is determined based upon a specific time and pressure relationship, not actual flow. So as I drive in the closed loop adaption window, the fuel adder will reduce itself and the injector duty cyle will be decreased, and in turn the fuel adaption adder too. It will be interesting to see if there is a small bump in boost at the very top end after the ecu realizes that it's no longer at max duty cycle at the very top of a loaded WOT run--or if that slight decrease is simply a built-in software safety net (don't know exactly which is the limiting factor, it's too close to call for the injectors). I will see though when I have the time to get everything setup.

Anyway, I'm having a bunch of fun here, learning a lot, and I hope there's no hard feelings.

posted by 67.10.24...

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