I have spend a couple hours reading through many scan/tune posts. Great info - Thanks.

I have a 1992 LT1. I'm looking to reprogram a few things. I know I want to at least change the cooling fan turn on temp to about 205 and to change the TC lockup speed to 50mph.

I have a universal programmer (GQ-4X) and have experience programming controller systems (programming and data) and burning to eprom. If I knew the addresses of the parameters couldn't I just read the stock chip, change the values at those locations and burn/program to a new chip and retain the stock chip for backup. I would go with a flash memory chip instead of eprom - the AT29C256 chip I think was mentioned.

I have not opened it up but is the chip socketed so I can just pop it out?

Is the chip data area spec available anywhere?

I see that I could buy Tunecat ($70) and the def file ($20) for the 92 LT1 (OBDI) but if I could do it without spending any money that would be good.

I also checked with PCM of NC and can get a one time chip tune for $139. It looks like their solution is a hybrid thing that still uses the stock chip with a daughter board. Wouldn't it be cleaner just to replace the original chip or am I missing something.

I might want to experiment a little after I get some simple things to work so programming my own would be better.

One other thing. What is a memcal, does the 92 have one and why would I care if I am just going to modify the eprom...

 

Great questions. The 93 is a 256k file, so when using a 27SF512 you assign hex 8000 and end 0FFF. To reprogram the original you either erase with ultra violet, or cut out, and solder in a new chip. You'll need an adapter from the memcal to chip burner. You will save your file first, or you can find them on the net too! The piggyback can simplify things if you are worried about soldering. They can actually be convenient, and can be used with zif sockets.
My website is dedicated to tuning TPI. See if these links may help:
http://www.scotthansen.net/links.html
Good luck!

 

Thanks for the response.

I have experience with proms but I see a lot of threads mention using a 512 chip instead of the 256. Sure you can by putting the data in the correct place but why would I even bother? The 256 chips are easy enough to get aren't they? I was going to use the flash chip at29c256 as it can be rewritten many times without needing an eraser.

Also, so you are saying that the chip in a 92 (and 93) is soldered onto the board and not in a socket. Then I can see why the piggyback stuff. I'm comfortable soldering but anytime you re-solder a chip on an old board there is a risk.

 

Those chips are getting hard to find, but the 27SF512's are cheap. I buy them 20 at a time though. Assigning the hex start is no big deal really, but if you can buy those older chips go for it. The chip is not in a socket, so you just cut it at the chip, and solder the new one in. It's actually pretty easy now that I've done it a thousand times. The adapter is a socket, and keeps your memcal intact. Search the moates site for plug adapter to put the memcal into the burner.
I've only ruined 1 memcal in over 10 years, and still have it on my desk as a reminder, and use it on occasion with a piggyback.

 

A Quick search online finds 12pc of at29c256 at $6.99 + $1.99 shipping...

Are replacement memcals available?

 

Long discontinued unless you find some NOS at a back country dealership
Were $300 ea when last available at least 5 years back

As Scott notes , usual practice is to install a adapter
http://www.moates.net/gp1-package-gm....html?cPath=31

in place of the stock memcal that has a ZIP socket for easy EEPROM replacement and provision for mounting the stock memcal on the side for the limp home programming


l]

 

If you really want to play around you buy this
http://www.moates.net/ostrich-20-the....html?cPath=95

Allows real time tuning adjustments direct from software on your laptop, even as you drive.
No need to program and R/R EEPROMs every time you want to change something in the tune

 

What I have done is pry the EPROM out of the MEMCAL. The pins come out with it because it's soldered in. Then you unsolder the pins from the EPROM and put them back in the carrier. Now you can plug in anything you like.

I made this MEMCAL programming adapter, but you can buy one like it from Moates (apparently I was holding the camera too close…):



You need to find a file for your car called a "hack". They are available by searching on your BCC (BroadCast Code) -- the 3 or 4 letter code on the silver label on the EPROM. Somebody took the .BIN file and ran it through a disassembler and then commented it. I believe it was Ward Spoonemore (RIP) who did the first one, aided by Bruce Plecan (RIP). Others started with their hack and used it as a basis for disassembling later .BINs. I know this is true because the same mistakes got propagated from hack to hack (for example, they got the VATS frequency wrong, and that was copied over and over again).

Ward Spoonemore's web site is long gone (he was known as ECMGUY), but here is a link to some stuff he did:

http://www.oocities.org/ecmguy.geo/software/

This site used to have a lot of hacs (they leave off the k for some reason I don't know -- probably something to do with the 8 byte DOS file name limit). I didn't look, so I don't know if they are still there:

http://www.diy-efi.org

After you get the hack, which tells you the locations of the parameters, then you need the .BIN file to modify and burn. .BINs are easy to find. I believe Moates has a zillion of them on his site.

One thing to watch for is that the code does a checksum on the data section and will set an error code if the checksum doesn't match. I have seen checksum calculators but never used one. Supposedly you can put $AA in the "program match byte" and it will bypass the checksum check. I tried that and it didn't work, so ???

I don't know what microcontroller was used in the later ECMs. My antique 1227165 uses a variant on the 68HC11 that has no on-board timers like the real 68HC11 does. Years ago I had a job where I had to program an 68HC11 in assembly language, so I have an original copy of the Motorola "pink" 68HC11 book.

There is now a free (I had to pay $100 for it several years ago) disassembler, assembler, simulator and burner IDE called THRSim11:

http://www.hc11.demon.nl/thrsim11/info.htm

One cool thing about this setup is that you can use the simulator to single-step through the code and see exactly what it does. The problem is that it takes a LONG time to do anything that way.

The ultimate debugger is a logic analyzer. I have a Hewlett Packard 1651B but I don't have the boot disk so it's a very large (and expensive) door stop. The crazy thing uses a proprietary HP disk format called LIF, which has 512 byte sectors and (even though I have the boot code) I can't format a floppy on my PC because it can't do 512 byte sectors. An IT expert friend of mine told me only certain (mostly very old) BIOSes can handle 512 byte sectors. He promised me months ago that he would create some disks for me… He told me recently he hasn't forgotten -- he just hasn't gotten around to it.