FMU, rising rate regulators and other non linear fuel devices on MAF based systems

[Jason Haines]

I was wondering if anyone has had any experience with using FMU's, rising
rate regulators and other devices that change the effective fuel injector
delivery in mass air flow (MAF) based systems that have had an aftermarket
supercharger or turbocharger installed. It would seem to me that the FMU or
similar device would compound the ECU's calculated fuel delivery unless you
were at the maximum duty cycle of the injectors (and the ECU couldn't
command anymore pulse width). With the ECU not knowing how large the
injectors really are (with the rising fuel pressure and unless the ECU has
a fuel line pressure look up table similar to some of the MAP based
injector flow look up tables), the ECU will provide too much fuel unless it
can't command anymore. Does this make sense? In a non MAF based system such
as a speed density system where the ECU does not recognize positive
manifold pressure so it cannot compensate for the added cylinder filling, I
can see how a FMU or similar device could work reasonably well but I see a
problem in MAF based systems. It would also seem that you would only want
the FMU or rising rate regulator to come into effect when the ECU no longer
looked at the O2 sensors for fuel trims so that you don't have very large
fuel trims from the changed fuel flow.


Jason

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Jason R. Haines				jhaines at lingenfelter.com
Lingenfelter Performance Engineering	219-724-2552 / FAX 219-724-8761
1557 Winchester Road, Decatur, IN 46733 USA
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sales at lingenfelter.com			sales and tech questions
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