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).

[PPPPPP42]

Ah ok thanks, if the netres is only programmed with a cylinder count that's what I wanted to know for swapping it into anything and everything. I'd be curious to read exactly how a pack of resistors telling the system how many cylinders it has allows the ECM enough info to limp home on a variety of engines.
Is there a reference guide for part numbers for the netres or do you just have to know what the ECM came out of by looking up the 4 letter code for the main chip if nothing else?
Also when I try to research the netres I see them called a calpac instead, am I getting my parts confused? According to that PDF I linked they all have an 8 digit part number when they are the seperate little chip like I think I have.

I knew the memcal was for the later stuff (92 with automatic and 93-95 with auto or manual for obd1 right?) though I got a little rambly and confusing. I was just commenting on the fact that it appears the 2 separate chips got combined into one big one on the memcal stuff from what I was reading.

EDIT: It seems that calpac (or pak) and netres are interchangable terms but if you want to order one from GM you are getting a calpac.
I also found out that:
"16060836 is the (V8) one.
16060837 is the number of the chip without the plastic carrier and IIRC its a GM internal number."

[EagleMark]

Have you ever watched the Big Bang Theory? Sheldon...

You'll have fun here other more knowledgable electronics guys. I'm more a car guy who learns as little as possible of electronics funtions, just what I need to make a car run... but I'll answer some.

It's really not a big issue, I have never needeed it to limp home and I've been driving these systems since 1988. I've done a lot of conversions and just stick V6 or V8 chip in... and never use it. Goal here is never need it!

1. Yes
2. Yes
3. I've seen heavily modiifed engines run on LHM. Not well but run, even stock does not run well but better, rich and not much timing or power. Safe but runs. Never intrested me how or why? I just fix the system so it runs correctly!

Memcals are more complex. There's some good threads around here on them. But not for the LH funtion, more run functions like cylinder count. It also has the knock module/ESC. One PCM covers more vehicles with a Memcal change.

No Etrans with these ECM so no trans funtions. TCC won't work in LHM, but I doubt you could drive that fast? There is a trans LH routine in etrans Memcal PCMs. But I don't recall it being part of Netres/Calpak.

The Calpak statement about gear ratios is not correct for these ECM/PCMs.There is a DRAC or VSSB that handles the gear ratio, speedometer signal from the VSS on the GM OBDI systems. Yes GM calls the little chip Calpak, people have called it Netres and some LH chip.

[PPPPPP42]

Funny you should say that, very not the first time I have been asked if I watch big bang theory (I have seen one or two) and been accused of being Sheldon.

I figured the gear ratio in any part of ECM statement was wrong as I just ordered a 7 pin dip switch (in quantity) to convert my drac so I can use the junkyard dirt cheap 3.73 gear axles I have (current is 3.42).

It makes sense that the older computers don't include transmission stuff in their limp home since they didn't change the ECM to a memcal type until the autos in 92 because of the need for the extra transmission controls among other things I'm sure (thanks for that year/application fact in another thread btw).

Eventually maybe I will tackle some GM engineer and get him to explain to me what the resistors do. Fake sensor data? Act as switches for preinstalled stuff in the computer? If its the second I would imagine they use the same set for different cylinder counts in all ECM's and its the stuff in the ECM it switches that changes.

I will also start looking at calpak numbers to see if there is really only one for each cylinder count or each ecm or what. I will look up the 4 and 6 cylinder calpak numbers for at least the 7747 (was this used in a 4 cyl?) later just to have them I think.

I mainly worry about the calpak being correct because many individual part failures will make it suddenly quite critical to getting home and I hate being stranded.

Most people do just want to learn how to make things work how they want without bothering with all the extra theory and details. It may seem stupid to want to know this much in depth, but if I know exactly what everything in the system does I can more easily learn tuning and diagnostics and predict what things will do. That's how I learned EFI in the first place, I just learned exactly what every part did and suddenly its super easy to diagnose EFI because I know which pieces are doing what jobs and I can rule stuff out based on symptoms and tests.
I also like to know in each type of ECM, what functions are in the ECM, calpak and prom.

There is a site out there where someone as messed up as I am was working to reverse engineer the calpaks to figure them out and even had the help of Moates, but I get the impression they gave up on it from what was on the site. He determined that building a custom one would be impossible since there is really no programming and any other type of resistor pack would be huge, not just a simple change like in the drac. He never did explain exactly how the resistors do what they do though.

[1project2many]

Limp mode is fuel only, no timing control. The NETwork of RESistors in the LHM chip is a simple analog calibration relating injector pulse to various input signals including coolant temp, voltage, MAP or TPS, and rpm. LHM can be duplicated and I know of at least one person who is having netres' made to include with remanufactured 2.5 liter engines supplied to the US Postal Service.

You will find that knowing too many details too soon will lead to a more complicated tuning process. Dropped in NYC with the goal of arriving at a specific destination, can you say the job is made easier or faster if you dedicate yourself to completely learning the subway routes, and street maps, and air traffic routes, and bus schedules, and "on call" service routes? You might make a helluva dispatcher when you're done but really, all that info to replace a simple set of directions? Or asked in another way, do you need to know how digestion works to enjoy a great meal?

GM did away with the redundant fuel devices in the '90s. The ecms are actually very reliable.

[romac55]

BUT , like Mark said ; once the smoke comes out , there's no way to stuff it back in . That's a great analogy ; finding a NYC address or becoming the best NY cabbie. Be safe...Bob.

[EagleMark]

I admire the intrest! But when your done you would be an expert on something that no one wants to use... never goes bad... and only comes into play if you mess up your prom burn or run without a chip...

[Six_Shooter]

I plan to one day, work out how the NETRES and RFD work in the P4 style ECM, but is not very near the top of my list. I did buy an O-scope as part of figuring out what does what on the NETRES, but I haven't found an official internal schematic of those NETRES DIPs, so I haven't started building my adjustable version yet. I know how I will I will go about testing changes, just want to make sure I'll have an accurate placement of the adjustable resistors to do it.

[PPPPPP42]

Ah, all very true, I should just start in a normal place and learn the basic how to's first.
Good analogy with the cab thing, though I'm the sort that would study all those extra things before choosing a course. I think I'm defective somehow.

I think I just got ahead of myself because I am always in shopping mode for future projects and asked myself, "If everything is in the damn chips why are there 50 different ECM's?" and so I wanted to know how everything was interrelated. I had sorta wondered if you could stick to a single ECM number (of a given EFI type of course) for absolutely any engine and just apply differently programmed chips for different projects, but the resistors for different cylinder counts in the netres baffled me and I wanted to know a little more about it.
I still have to figure out why people pick one ECM over another and the differences between any 2 basically functionally identical (not including chips) ECM part numbers.

At the moment I am reading the educational stuff on the Moates site, but I can tell it will leave holes, especially where the extreme basics and the more specific application stuff is concerned. So I will have to study elsewhere as well.
Is there a more basic list of electronic hardware somewhere with pictures and explanations? I still can't name any of the individual parts in that "chip sandwich" I linked to in my first post just by seeing them or tell what they are for.
EDIT: nevermind, after reading that G2 install instructions about 12 times and rebrowsing the catalog I think I get what is called what and what everything is for and what parts you skipped to make it lower profile which seems a really good idea.
That socket booster 1.0 seems to solve a problem with the ECM I was specifically looking at, is this weak communications a common issue? I don't know how much emulation I would be doing as I barely understand its purpose so far. If soldered to my ECM directly it seems it would eliminate several other pieces from the stack.
http://www.moates.net/socket-booster-1-0.html