Re: PI closed loop algorithm for 1227747 ECU?

["Bruce Plecan" <nacelp@bright.net>]

From: "rr" <RRauscher@nni.com>
Sent: Tuesday, July 04, 2000 11:01 AM
Subject: Re: PI closed loop algorithm for 1227747 ECU?


The little guys and I again thank you for shedding more light here
Grumpy



> For the cl idle, reduce the prop gain at 0x2f9 to 1. Might also
> want to go to a larger vac line to the map. A 1/4" line helps
> when engine is cam'd.
>
> If the idle is osc due to iac movement, increase (slightly!), the timer
> vals at 0x5C7 through 0x5CA.
>
> Should have a GM O2 sensor, the response time matches the
> the PID loop better.
>
> Prop gains. May need to be reduced, tables 0x4A8 & 0x4C7. Prop
> gains are interesting, they always work to bring the O2 val in the
> opposite direction, it lean, prop adds fuel, if rich, removes fuel.
> Sometimes it can be too drastic, causing over and under shoot.
>
> If backfire is through exhaust, there is a decel enleanment table
> at 0x3FA, big blocks have some huge numbers there. Don't
> worry about the int and blm's moving a bit, stock engines are
> the same way.
>
> BobR.
>
> Might be worth getting an EST distrib in there. The other
> half of the drivability is in the SA.
>
> Scott Lundahl wrote:
>
> > Hello everyone.  I'm new to the list and this is my first post.  I'm
doing
> > an FI addition to a 1980 Triumph TR8.  This is the car with the GM 215
(3.5
> > liter) cid aluminum block V8 derived Rover engine.  OEM fueling for this
> > (49 State) car was via twin Zenith carbs in the usual British style.
The
> > California version had Lucas (really Bosch L Jetronic) port fuel
injection.
> >
> > On my car, the original Zeniths were later replaced by a good old low
tech
> > Holley 4 barrel and Edelbrock Performer manifold.  I added a tame to
medium
> > cam and headers to perk things up a little.  This setup ran OK, but
lacked
> > many of the usual amenities such as a choke that worked properly, idle
> > speed control (yes this car has A/C) and so on.  It was also OPEC's
dream car.
> >
> > So I decided to add non-eom FI to the car (the eom systems have no
> > performance potential and are incredibly expensive).  I chose a TBI
system
> > using a 1227747 (C3 series) ECU because it interfaced easily to the
current
> > setup in the car.  The C3s are also easy to manipulate via EPROM (which
is
> > good because I have burned many so far).  This system is driven by the
> > stock (non-ESC) distributor via a buffer.  A heated O2 sensor is on the
> > header collector (4-2-1).
> >
> > Anyway, I have the system in and dialed in to the point where it will
run
> > with perfection when I set the ECU to run in Open Loop mode.  It will
run
> > well with the fuel map set for slightly lean or slightly rich.  However,
> > when I set it to run Closed Loop, the system develops a light throttle
> > cruise surging (very annoying) and backfire on decel (I can almost
> > eliminated the backfire via the decel params).  It also wants to
oscillate
> > at idle.  The BLMs tend to wander all over the place.
> >
> > Since things seem to run OK in Open Loop when fueling is slightly rich
or
> > slightly lean, running at stochiometric does not seem to be the problem
> > (some engines just don't like to run there).   There must be something
> > about how C.L. operation is accomplished that is causing an issue (check
my
> > logic here).  Therefore, I suspect that the PI parameters (gain factors,
> > time delays, etc) may not be correct for this engine (this is somewhat
> > plausible when you consider that this ECU was originally setup to
operate
> > with an engine 50% larger or more than mine).  Thus it operates at a
point
> > that is close to instability in C.L.  So, I have two questions.
> >
> > Does anyone have any suggestions / experience / solutions with a similar
> > symptoms?
> >
> > Does anyone have information on how the PI algorithm operates on this
> > ECU?  I have seen such details of how the spark control algorithm works.
I
> > also have the detailed hack of the type $42 (this is an incredible piece
of
> > good work) but the comments in the PI section aren't quite detailed
enough
> > to reverse engineer what's going on.
> >
> > Any help/suggestions would be greatly appreciated.
> >
> > Thanks,
> >
> > Scott
> >
>
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