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Well, this is the way that I inderstand it.
Not all map sensors are the same, the fuel pressure regulators are different, folks run different exhausts etc. So these variable need to be compensated for.
While cruising off boost, the ECU looks at the mixture from the O2 sensors point of view. It arrives at compensation factors that makes everthing work.
When you install a resistor mod, things can run rough until the ECU readapts, so I have been told, and that makes sense. Based on these adaptions the ECU knows how to map fuel up to its map limitations, and more often up to the artifical boost limitation of the fuel cut.
Now if you put in a resistor mod that is too big, so fueling will be an issue at high speed, the ECu will take care of that too. It is now having to add much more fuel at what is percieves to be a low pressure, remember it does not know about the real pressure. After is had adapted for a while, it will notice that the injector duty cycles are too high for the lower rpms and pressures where it is running where it can actively adapt. So it triggers a CEL, even though it can drive ok. Why, because if the duty cycles are too large at what it beleives to be modest power demands, then it cannot be expected that there is enough remaining injector capacity for WOT at high rpm's. So there can be an adaption fault based on safe limits for injector duty cycles and there can be a CEL for a hard adaption fault were the ECU cannot get the mixture right during mild power demands.
So if you don't get a CEL, things are pribably fine. If you do you can raise the redulated fuel pressusre and the ECU will adapt and see a smaller injector duty cycle and things then run ok.
With a MBC, you can do anything that you want because there are no conditions under the fuel cut pressure where the ECU cannot map fuel with low injector duty cycles, and the map was not changed do there are no adaption issues at all.
You can add around 380 ohms and get 17 psi of boost. You may need to 'crush' the regultor to get the pressure up, or add a series regulator downstream. Thing will sort themselves out. When you do this the fuel cut pressure has probably gone to over 20 psi.
But if you add a small resistance and use a mbc, the change is mild, the fuel cut is moved a modest amount and the adaption chanlleng is small. And you can mbc to 15 psi and let the ecu should ignore the boost overshoots.
I don't know if that addresses your concerns.
posted by 208.24.179...
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