[Diy_efi] checksums

[Adam Wade]

--- - <titkoscim at maffia.hu> wrote:

> I just wondered if checksums can be eliminated. I
> know there is a reason to use them, but when
> experimenting with chips, it would be nice to 
> eliminate the checksum code with nops...

The main reason to use them is that many ECUs check
the checksum when "booting", both to insure the
integrity of the data and to make it that much harder
to hack.  So the "reason to use them", in the case of
many aftermarket/end user folks is that the car won't
start without the correct checksum being in the
correct place.  :)  To me, that's a pretty good
reason.  :)

> and, how can one figure where to find the input
> data? like RPM sensing, MAF sensing, and so on.

Data?  What kind of data?  You want to data log the
analog outputs of the individual sensors?  That's easy
enough, but signals like the crank sensor will require
a lot of processing before any real "sense" can be
made of them from a human standpoint.

> realtime logging would be just great for this 
> and make it easy, but on older systems I doubt there
> is a way to do, or?

You do it the same way on all pre-ODB II systems; buy
(or build) a data-logging box with A/D converters,
wire in a T to each sensor you want to log, and you're
done.  On OBD II and later vehicles, there exist a
number of commercial products that can log the sensor
data right from the OBD II connector (this is one of
the things that's mandated by the OBD II standard,
that emissions-related engine data be available
through a standardized interface for emissions repair work).

=====
| 82 Honda CX500 Turbo (Cassandra)  90 Kwak Zephyr 550 (Daphne) |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |
| M/C Fuel Inj. Hndbk. @ Amazon.com -  http://tinyurl.com/6o3ze |

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