Control selection

[Dale Ulan]

> >How can the C3 TBI ECU do a smooth idle with large roller cam?

You'll need to change the fast/slow MAP filter coefficients and mode
coefficients. That's a start. You may need to play with the IAC
coefficients, but the code was not designed to compensate for a big
cam, so you may have to live with a slightly rough idle. Maybe raise
the idle speeds.

> >Is an interface and program available to use the ALDL with a laptop PC?

Yes, but you can't see that much on a C3. Mostly just sensor readings.

> >Does the C3 optimize ignition advance for power/# of fuel or only retard if
> >knock is sensed?

Retard only, in general. However, there is a premium fuel flag which is
set during half of the ESC diagnostic. It may or may not be enabled,
depending on the code version. I believe most applications have this
flag disabled.

There are many code versions that run in a C3 ECM, and each PROM map is
majorly different. I could point you to the right locations if you were
driving a 1989 through 1992 GMC pickup truck with a hydraulic transmssion
and a 350 or 305 engine.

In any case, the C3 ECM is very limited in memory, and often has only
enough RAM (like every byte is used) and enough ROM (30 to 40 bytes
free). The serial port is slow and uni-directional. The best way I've
found to figure it out is to read out the EPROM and masked ROM, and start
disassembling. That's how most of us on this mailing list do it.

If you have the same code version, code will start at $d617, where the
EPROM is mapped from $d000 to $dfff.

Generally, there are few PROM editors around on a PC because of the
large numbers of different code versions around. I haven't seen any,
although there may be some for certain versions of the code.

-Dale