[DML] Re: Megasquirt Fuel Maps

["Matthew" <drivestainless@xxxxxxxxx>]

Hi Richard, and everyone else,

Bill saw my car yesterday, which has a 3.0L PRV with a B280F throttle
body, running Megasquirt II and the Ford EDIS ignition.

Bill mentioned to me during his visit that K-Jet owners have idle
oscillation.  What I explained to him was that Megasquirt users can have
idle oscillation as well.  One reason being a relatively  "large"
discrepancy between adjacent cells in the fuel or spark tables at idle
which causes the mixture, and thus the idle, to oscillate.  Yes, the
system does interpolate between cells, usually several at a time, but
having just one value out of range can create an oscillation. 
Ironically an idle valve can sometimes make the problem worse as it
attempts to counter the oscillation.  Using the tuning software, I can
force my engine to oscillate the idle and post a video as an academic
gesture if there is disagreement over this.

Someone mentioned about EFI using a closed loop system with feedback
from the oxygen sensor.  I believe by default, in Megasquirt, the oxygen
sensor doesn't become active until > 1500 RPMs, so this is a moot point
with respect to idle.  There are many other reasons for idle oscillation
which a Google search will quickly reveal (megasquirt idle
hunting/oscillation).

I did not mean to imply that idle oscillation was commonplace among EFI
systems, but wanted to show Bill that the mere fact that you're using
EFI doesn't preclude having some of the same problems you would have on
an antiquated fuel delivery system.

I do think that a universal kit could be made, but providing support for
it would be practically impossible.  Additionally, some owners may not
be willing to make the drastic changes to the car which provide (in my
opinion) the best cosmetic and practical results (i.e., removing the
fuel accumulator, cutting and splicing wire harnesses, modifying
brackets to hold new components, removing and adding new circuits to the
stock fuse box, etc).

I did many of these things because I did not want the car to look like a
DeLorean where EFI was added - I wanted it to look like a stock EFI 3.0L
DeLorean.  Even Bill shares this view in part of his carbureted car
because he's added updated vacuum routing diagrams, removed unnecessary
wiring, and sealed off holes in the fiberglass where components no
longer are in place.

Matt
#1604







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