Whats in the ECM and whats in the programmable chip?

[PPPPPP42]

In hunting for a 7747 ECM I have found there are any combination of engines and transmissions that use that part number. Obviously its nice to get the correct one from the start, but if I will just be pitching the chip on it and putting a new one in its place such as this:
http://support.moates.net/g2-adapter-installation/
Does it really matter what ECM I get so long as its a 7747? Where is the info for engine and transmission and what not stored, I think I just read in another thread its on another chip in the ECM. If so is that chip reprogrammable or replaceable?

Is it possible for a 7747 to be completely universal so that I could move it to any TBI vehicle it will plug into and just swap programming?

EDIT: Btw that chip sandwitch you end up with following the instructions in that link is slightly hilarious, youd think someone could have come up with a more direct adapter.

[EagleMark]

1227747 are all the same. There is a smaller chip called a Netres that is the Limp Home. If catastrophic failure occurs in EFI system it has safe settings so engine still runs. These are differant V8 to V6 etc...

I solder the Moates G2 directly into ECM without dip sockets. With chip you can still install cover. No sandwich effect. Use a zip socket to emulate or while changing chips.

[PPPPPP42]

So two identical number ECM's aren't actually fully interchangeable unless they came from a vehicle with the same engine and transmission unless you swap the smaller chip out?
So what can be done with the smaller chip if you want to use the ECM in something else, especially if its an application that never used that ECM or another brand vehicle entirely? Do you just lose limp home mode? Is that the only difference other than the main chip then?

[JeepsAndGuns]

If you are wanting to run a V8, get a 7747 from a V8, that way the smaller "limp home" chip will be the correct V8 one. You can use a 7747 from a V6, but you will need to swap the limp home chip for a V8 one. Works the other way around if you have a V6. Its usally easyer to find a 7747 with the correct chip in it, than to find the chip by itself.
So yes, all 7747's are fully interchangeable. The limp home chip is what needs to be engine specific (V6 or V8). And of corse the main chip too.
Lots of people have converted older non fuel injected engines to fuel injection, myself included. What are you wanting to add injection to?

[EagleMark]

Even though they all have 1227747 on them, the BCC is differant for the chip and I guess it gets the matching netres. I just use a V8 or V6 netres depending on engine going into. No big deal here really in any vehicle. The main chip is the guts of the operation, small chip is LHM.

If you buy a new ECM it comes with no chips. You use the chips from faulty ECM.

[PPPPPP42]

Its not that I can't find the correct ECM I just want to understand exactly whats going on but in the past people kept telling me the correct thing to do without fully explaining what everything does which teaches me nothing.
Not looking for specific answers to a problem, just general theory.

So if I have this straight:
1. Without the 2 chips installed ECM's with identical part numbers are 100% identical no matter what engine, transmission, vehicle or year they came from.
2. The larger chip can be replaced with something that can be programmed for any engine of any size or brand or modifications so long as you know what you are doing.
3. The smaller chip is not reprogrammable and no aftermarket versions exist, and must be the correct one for the exact engine setup, significant mods to the engine or a change in engine would render the limp home useless and so the chip would have no purpose.

So unless you are using a stock engine or an engine close enough to stock that there is a limp home chip available for it then it doesn't matter which ECM of the correct part number you use because the limp home chip will be wrong and not allow the engine to run anyways.

Just to clarify the smaller chip is ONLY for the engine or does limp home include transmission data like the main chip does?

EDIT: I should specify again this is for the 7747 ECM which is the earlier style with the resistor pack chip totally seperate, I get the impression the later MEMCAL stuff has the things incorporated into the same chip thingy. Do keep in mind I am just starting to learn this stuff and may have misunderstood some of the basic fundamentals.

2nd EDIT: ok so I get the impression from this:
http://www.bsecorp.com/files/techtips/bdtecb103.pdf
that the 7747 is prom with separate CALPAC and the later MEMCAL assembly has the calpac built in.
Is the calpac resistor data generic sensor data that would work with any motor using the same sensors? I really want to fully understand how it does what it does.

I found this on another site, is this accurate? "A Calpak, a separate chip on the Calibrator Modules, normally provides the information to the ECM for rear axle gear ratio on pre 90 models."
That would mean that the Calpac is doing more than I thought.

[FSJ Guy]

You were good on 1 and 2. #3, sort of. :D After that, it starts to get fuzzy. "Technically", the 7747 ECM doesn't use what are called Memcals.

Sooo.... Back to #3. The smaller chip "Netres" is a NETwork of RESistors. Hence, the name. It has the limp home information that is used if the larger programable chip goes Kablooey. They are known to be different for V6 versus V8 engines. That's it. If you're running a 6 cylinder, get the one for a 6. If you're running an 8 cylinder, get the one for an 8.

What if you have a Chevy 454 V8? 8 cylinder Netres.

Got an inline 6? 6 cylinder Netres.

How about an AMC304 V8? 8 cylinder. What about a 401 V8? 8 Cylinder.

See where I'm going? All you have to do is match the cylinder count. For most people, that's all you need to worry about.

As you already know, (See #2), the "bigger chip" can be replaced with a user programmable chip to account for a whole host of different engine and vehicle parameters.

Memcals and such are usually the names given to "chips" on other more advanced ECMs (mid to late 90s).