Big overlap cams and EFI

[James Boughton]

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Joe,
	The MAP sensors I've used are actually very responsive (high frequency =
response).  I'm not sure about GM's, though.  So for utilizing the MAP =
sensor signal for the ECM there is usually some sort of filtering =
routine.  For example, I am familiar with one ECM that reads the signal =
on two edges of the crank sensor and averages them.  This average is the =
reading that is used for the fueling and spark control.  It may be that =
the higher pulsations in the intake system with the larger cam are more =
than the averaging routine can handle.
	On the other hand, it may be possible that the pulsations due to the =
larger cam cause the ECM to trigger acceleration enrichments, which I'm =
not sure anybody other than GM knows how to calibrate for their =
controller.  Maybe someone could fill in this information for me.
	There are also any number of diagnostic routines that may be effected =
by the change in idle MAP.  Did the PROM burner guy give you any more of =
a hint as to what the problem is that arises from longer cams?

Jim Boughton
boughton at bignet.net
Owner - Boughton Engine Systems Technology (B.E.S.T.)

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