1226026 - Crossfire

[NeilBreakwell]

Hi, Guys -
Just starting to learn about the fascinating world of GM ECMs ...

Have a 1983 Trans-Am with the 305 Crossfire engine.

ECM ID number is 1226026 and PROM has the following markings on a sticker:

DELCO
ASY
5597

Anyone know what the "PROM mask ID" is for this ECM/PROM ?

many thanks

[stew86MCSS396]

https://pcmhacking.net/ludis/c3xref.html#1226026

[1project2many]

Hello Neil,

I have some 6026 Crossfire calibrations but I do not believe I have definition files. I have never found them! The prom is OTP, One Time Programmin, so it cannot be reprogrammed. Many folks find the better option is to use a later 7747 or 7427. I opte to install the 7747 then moved up to the 7427.

[NeilBreakwell]

Thanks, guys ...

@stew86MCSS396 ...
Does the "program ID" in this link ($0F) refer to the PROM mask ID ?

@1project2many ...
forgive my ignorance, but what is the "7747" and "7427" that you refer to ?
alternative ECM numbers which are interchangable ?

best
- Neil

PS - appreciate that the PROM is one-time-programmable, but I'm guessing that I could replace with 2708, 2716 or 2732, which are all 24 pin DIL devices ?
May have to think about what to do with the chip enable lines though ?

[steveo]

i know its disappointing, but that's a horrible ecm to use for learning. in the 'fascinating world of GM ECMs' we would rip that thing out and replace it with something else. if you search this forum for 'crossfire' i'm sure you'll find other people that have done that.

nobody has really been able to (or spent the time on) reverse engineering those calibrations (maybe because the ECM isn't very good anyway), so you'd be working blind.

i've tuned other ancient ECMs that did have some research done on them already, and most of those early ECMs are primitive to the point of being useless for modified engines

even if you manage to find a way to tune it, your hard work wont give you the kind of control you're looking for. it probably has a 4x4 fueling table or something and most of the other math is hard-wired outside of the calibration. redneck tuning it with an adjustable fuel pressure regulator or a potentiometer on a map or temp sensor would probably give you similar results if you just want to bump fuel a bit.

...unless you're doing it 'because it hasn't been done', in which case i take all that back.

[steveo]

here are some bins that someone has pulled from 6026 ECMs...

http://www.gearhead-efi.com/gearhead-efi/bin/1226026/

[NeilBreakwell]

Thanks for the advice - it is much appreciated.

However, my goal is really to understand the ECM in my car down to the level of the firmware, rather than to tune or tweak it. So I guess I am doing it "because it hasn't been done" :)

So, the challenge is set - if I can figure out the PROM mapping for this ECM, I'll be sure and share it with the world :)

[steveo]

how about start by taking and posting high resolution pictures of both sides of the board

[NeilBreakwell]

On it ...
but first will remove some of the odd "gunk" that appears to be spread around a couple of the ICs. There are actually two back-to-back boards in this unit. One has the connectors and drive components, while the other has the PROM and five 40-pin DIL ICs.

Will post pics in next day or so.

You will notice some burned components on this board - this is a spare one (not the one driving my car)

[steveo]

oh, good you have a spare... usually with old stuff like this, the calibration is on that main chip (your 'bin files') but the junk that reads the calibration and runs the engine is on some roms, so you're reverse engineering several chips.

i hope you know or plan to learn to reverse engineer whatever low level language this thing was developed with, otherwise turn back now...

[1project2many]

I believe they are 68HC09 equipped.

You know, I almost remember waiting for the vacuum tubes to warm up before the Crossfire would start.

[NeilBreakwell]

Thanks, 1project2many - that is a great help. I had been looking at the pinout for the 16021633 IC, which I found here:
https://pcmhacking.net/ludis/c3pinouts.html#16021633

and concluded that it was similar to 6800, but knowing it is 68HC09 is great

Unfortunately, the cross ref of 16xxxxxx part numbers to function here:
https://pcmhacking.net/ludis/c3pinouts.html

doesn't include the other 16xxxxxx chips that I see on the board, ie:
21632
16021634
16027202
16027203

I'm guessing that these must be ROM or RAM or IO controllers or some combination.

I'll have a better idea when I trace out where all the address and data lines go to on each device, now knowing which are which on the PROM and the microprocessor :)

[In-Tech]

Hopefully this will help you a bit if you don't already have it. This is NOT a zip file so change the extension to .rar as it is actually a winrar file, the forum doesn't allow .rar attachments so I changed the extension. Maybe a mod or admin could change the forum to allow .rar files. This file will pretty much cover all the instruction set for the MOT 68xx family.

[NeilBreakwell]

10-UpperBoardTop.jpg11-UpperBoardBottom.jpg12-LowerBoardTop.jpg13-LowerBoardBottom.jpg

[NeilBreakwell]

Many thanks for that ... are you saying that the micro is equivalent to a 6805 ? Can't actually find a pinout for that part number in this document though.