anti-theft chips ?

[Dave Zug.]

----- Original Message -----
From: Programmer <nwester at eidnet.org>
To: <gmecm at diy-efi.org>
Sent: Thursday, October 05, 2000 2:02 PM
Subject: Re: anti-theft chips ?


> I'd think that any type of anti-theft system may be a hodge-podge in an
> emergency...
> I'm not much of a software compiler guy, Dave. Been years since I wrote
> basic <G>...if I wanted to do this in
> a 7747 bin--how'd I do it ?? I know somebody wrote code to
> put a speed limiter in a 7747 bin--and it works great. If it's shown
> to me once...I'm a quick learner. I've seen this before somewhere in my
> internet travels, but can't remember where. Somebody mentioned a
> "secret start" sequence -- maybe it was at the GN site, I dunno. I'm not
> sure
> if this would work but, how'd you write:
> 1. If Key on

immediately after the checksum routine place a pointer to a blank location.
checksum is run at key-on, therefore the patch will run immediately after
checksum success.

> 2. If TPS + 70% or A/C signal high, or .... PRNDL in R_DL once

Compare present TPS reference ram location with a $80 or something. If .GT,
then set a ram variable (gotta find an unused bit flag) to true. If not,
False.

When it comes time to lookup the, say, RPM limit, point to a unused prom
location insted of the standard prom location and set it to 1 (25 rpm?) IF
the contents of the flag you set earlier shows improper TPS at key-on.

> 3. Then fuel on ??

I wouldnt mess with fueling - of coarse on a bench it won't be dangerous.

> Will the PCM see this as a one time event at start up--it should I guess?
> If you don't have time help--no problem...I'll try to figure something
out.
>

I'll try to dig up the code sections. There are 3 areas: JSR after checksum,
subroutine to compare TPS and set flag, and decision to set the spark table
pointer, whick uses another subroutine.  In order to do this WITHOUT
recompiling, the areas in the assembly code that must have JSR's inserted
have to REPLACE a certain amount of code, therefore the FIRST thing to do in
the subroutine is to complete the code that you wiped out for the JSR
instruction.

Again - ON A TEST BENCH!

> Lyndon.
>
> -----Original Message-----
> From: Dave Zug. <dzug at delanet.com>
> To: gmecm at diy-efi.org <gmecm at diy-efi.org>
> Date: October 5, 2000 7:58 AM
> Subject: Re: anti-theft chips ?
>
>
> >in '97 or so, I patched in code (manually - no compiler) after the
checksum
> >to check TPS and compare it with 50%. checksum occurs at key-on and not
> >otherwise (from what I could find - no other calls to the start of the
> code)
> >based on the comparison I would select 1 of 2 spark tables when it came
> time
> >to do the 3d lookup. I suppose if you either put the execution into an
> >endless loop if TPS is not above 50% when the key is turned on.
Interrupts
> >may override this though. I made a lengthy post regarding exactly what I
> did
> >maybe a year ago. another consideration is liability of coarse.  If the
car
> >must be started in a panic, or BORROWED in an emergency it could gum
things
> >up. If an accident occurs it will take high paid experts to testify that
> >there is no way your patch was responsible.
> >
> >DISCLAIMER - DO THIS ONLY ON A TEST BENCH, for fun  ;-)
> >
> >EFI performance made a security version for their GN chips that required
a
> >sequence of activities, something like key, neutral, park, TPS, crank.
> >
> >
> >
> >----- Original Message -----
> >From: Programmer <nwester at eidnet.org>
> >To: <gmecm at diy-efi.org>
> >Sent: Thursday, October 05, 2000 2:35 AM
> >Subject: anti-theft chips ?
> >
> >
> >> Anyone ever figure how to write a secret start sequence so
> >> one wouldn't have to shell out big bucks for an anti-theft
> >> system that is so easily bypassed ? My secretarys' husband
> >> had their 89 C1500 SWB stolen right from in front of their house.
> >> They heard the truck start up and drive away--thought it was a
> >> neighbor <g>. That was last week--got the truck back today,
> >> luckily--the idiot that stole it was caught driving drunk...otherwise
> >> they probably wouldn't have had any action on it at all...
> >> Lyndon.
> >>
>
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