7747 tuning again

[rr]

Hi Walt, I was starting to wonder if anyone was reading my posts <g>.

Here's an introduction that I've put together. . .

BobR.

GM ECM Data Collection System, Lockers

Robert Rauscher, 4/9/00

General:

    The Lockers system described in this article is for use on the
    '747 ECM. It will work on some other ECMs without changes. Other
    ECMs will require minor changes in the Lockers system.

    The purpose of the ECM Lockers system is to collect ECM data and
    vehicle data during the live operation of a fuel injected
    automobile engine. This data is then evaluated 'after the fact'.
    An evaluation program is used to analyze and display ECM
    information directly related to the performance and tuning of
    the engine and drivetrain.

    This evaluation program is used after the data has been
    collected. Drag runs, cruising, and driveability situations can
    be collected and evaluated.


The Hardware:

    The data is collected from the ECM 'service port', which is
    nothing more than the CPU bus. The collection hardware does not
    interfere with the operation of the ECM, it is transparent to
    it. This board simply plugs into the service port connector.

    The data collection hardware has three sections:
    A section to save the ECM data locally, a section to read that
    store of data and transmit it, and a timing section. A RAM chip
    and some mux's comprise the data storage section. A Microchip
    PIC is used for the communications transmitter, while some
    single-shot devices provide bus synchronization and timing.

    The collection hardware is also powered from the service port.
    This includes the serial interface which uses a MAX232 to
    provide RS-232 signal levels.

    The PIC has eight analog input ports available. A planned
    enhancement is to add exhaust temperature monitoring with eight
    thermocouples in the headers. This data would be collected and
    transmitted along with the ECM data.


The Data:

    The data collected is the entire RAM area used by the ECM.

    These 256 bytes of data contain information from all of the
    sensors, scratch pad for calculation routines, stack area,
    bit-mapped flags, and more.


The Communications:

    Data is collected by a laptop is to be analyzed later. A serial
    receive program for the laptop is provided. A standard terminal
    program can also be used for data collection. The program
    provided has the additional functionality of timestamping and
    point-marking the data stream.

    Data packets are transmitted at two user selectable rates:

    38.6Kb, 10 frames per second.  (153.6 KB/minute, 9.2 MB/hour).
    57.6Kb, 15 frames per second.  (230.4 KB/minute, 13.8 MB/hour).

    So, at the higher rate, you can gather every bit of the ECM's
    RAM data fifteen times a second. The transmission rates are
    limited by the laptop that is being used. The above rates were
    obtained with an old 386sx @ 16MHz. That was the best it could do.

    Using a 486 @ <anything>, would easily obtain 115KB with 30
    frames per second. Minor changes to the Lockers system are required
    for the higher transmit rates.

    The data is transmitted in packets of 260 bytes. Starting with
    two sync bytes, 256 data bytes, ended with two checksum bytes.


The Evaluation:

    Once the data has been collected, it is available to be evaluated.
    A PC-DOS program is provided that displays in tabular form, various
    selected data information. The eval program converts the ECM data
    into real world numbers: rpm, mph, drp cnt, map, tps, injector pulse
    width, pump shot, o2 sensor, and more. The data values to be shown
    are user selectable.

    The evaluation program also calculates and displays acceleration
    rates, and crankshaft torque. Fuel consumption calculations are
    currently an in progress enhancement.

--


Walter Sherwin wrote:

> Hmmmm.  Wanna elaborate a wee bit?
>
> Walt.
>
> > Around Christmas, I'm going to release a data logger that
> > will put any aldl interface to shame. It will be for the
> > C3 ecms.
> >
> > BobR.
> >
>
> ----------------------------------------------------------------------------
> To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org