Re: PI closed loop algorithm for 1227747 ECU?

[rr <RRauscher@nni.com>]

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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