From: Kukukooter@aol.com@INTERNET on Tue, Nov 26, 1996 9:39 PM
In a message dated 96-11-26 17:30:44 EST, Dave_Clement-LDC009@email.mot.com
(Dave Clement-LDC009) writes:
>> At Wide Open Throttle the computer is not operating closed loop. It
>>reverts to look-up tables to decide on injector duty cycles and timing
based >>on>a subset of the sensors.
>Very interesting, though this does conflict with the programing of the 20
>Eproms. The computer would have to have multiple sets of tables to taylor
to >each different driving situation. Your explanation makes perfect sense
to me, >but doesn't explain why fuel injector pulse width is "set" to
grandma's >driving, then reprogrammed to Mr. Leadfoots driving. My time's at
the track >have been close to a half second slower when my wife has been
driving it all >week, then back up to speed when I 've been punchin it all
week. This means >that a table, that is specific to that particular engine,
would be established >at WOT. Who knows? As for the MSD,Crane,etc giving a
better idle due to a >multiple spark, I tend to doubt that it is needed on
these motors.
>Multiple spark is needed for cams with lotsa overlap (40+) up to 3000rpm
then >the spark becomes one big spark thereon. The Crane has the option to
disable >the multiple spark below 3000rpm which is the option I use. The rev
limiter >also confuses the SBEC by removing spark, and if the stock or
emission legal >cams are used, you don't ever have enough overlap(shitty
idle) to require a >multiple spark below 3000 rpm. But in doing the job as
a burner of excess fuel, >I'll admit nothing gets by my chambers unburned,
making this Dak pass emissions >with an A+. Thats why I can't seem to
picture the aftermarket units >"Controlling the timing" and the SBEC sitting
pretty...penny
>for your thoughts...NOW, will an aftermarket ignition cure detonation???????
???
I had a fairly lengthy discussion with one of the engineers that was
involved in the programing of the 2.2 turbo SBEC's. His explanation for the
open loop at WOT was that many of the sensors used for closed loop operation
do not react fast enough to keep up with the needs of the engine. His
explanation was that the look uptables provide logic for the SEBC to decide
what the engines needs are going to be based on what has been happening.
This guy had worked on the 2.2 turbo stuff where there was a minimal amount
of adaptation by the SBEC. I would venture to say that where there is a
large amount of learning going on that the look-up tables are over written
as the SEBC learns how the vehicle is driven and there is no reason not to
expect many of these parameters to be updated at less than WOT. This would
explain how granny driving the vehicle for a week would effect your 1/4 mile
times on Sunday and also why disconnecting all power will get the engine
back to it's basic defaults.
Something you said above caught my eye. Why would you think that there is 20
EPROMs in one of these controllers? (thats an awful lot of memory) I have
opened a couple of older units and there was a processor chip a couple of
EPROMS to hold the basic programing, a couple of RAM chips and a bunch of
A/D and D/A converter circuits. There was also a number of high power rated
descrete devices for running the injector, ignition and charging circuits.
All in all not very impressive when compared to your basic Pentium mother
board.
I have no personal experience with the aftermarket ignition boxes but all
the ones I have seen or read about go in series with the ignition not
replacing it. Other than giving a hotter spark an multiple spikes they have
no effect on timing. I have read that some are supposed to compensate for a
leak cyclinder but if that actually happens it is likely because the box can
sense how the feild is collapsing in the coil and react.
Some of the 2.2 turbo guys have these engines pushing 300+ HP. It's done by
using big turbos, big injectors, very high boost pressures. The components
are way outside what the programing of even the MP SBECs were set up for so
at idle gas is almost dripping out the exhaust. The MSD box helps with the
idle and under the high cylinder pressures. There is a member of the local
Shelby club that has a Caravan running in the 12's with a 2.2 turbo.
Dave Clement
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