My elusively clandestine 1995 TBI VCM?

[ReadyXB]

I am here out of desperation, having searched to my hearts content for information on whether or not my computer can be modified.

First, what I have:
1995 S10 LS, 4.3L V6, LB4, VIN "Z", "TBI 220", balance shaft, and it is RWD with the NV3500 M50 manual transmission.
The computer is a VCM, and not the PCM or VCM-A. It is black and is located on top of the coolant overflow tank at engine bay left (er, right):



The barcode sticker on the VCM says "ECM SERV NO. 16230703" and also 16230715



Removing the chip cover reveals a blue plug-in module (2x18 female) with the following numbers on it:
5165
1616
8417





I am mostly done with a complete rebuild of the engine. I have gone with a larger camshaft and anticipate needing to modify the base fuel map in some areas. I would also like to prevent the soon-to-be-absent EGR to not cause a MIL as I will leave EGR off.

Does ANYONE know what I have here and can it be modified? I have a good background on tuning and programming, writing firmware, etc, just not with the GM TBI VCM, so I have a lot to learn! I have looked at all of the chip adapters at moates.net, but I didn't see any that matched my module's 2x18 (36 pin) socket.

Thanks for any help!
-ReadyXB

[Six_Shooter]

If that is actually the PCM that blue piece is simply a knock filter and has nothing to do with the actual tune or bin file. It will be a flash based PCM, meaning that if one is available you will need to find a cable that connects to the ALDL plug to change the tune that way.

[ReadyXB]

Thanks for the reply! In that last picture, the socket shown is the PROM unit socket, and the blue module is the PROM unit. The "Driveability, Emissions, and Electrical Diagnosis Manual" for my S10 has the part identified as the PROM/MEM-CAL. The computer is a VCM (used on 4.3L "Z" with manual tranny) and not a PCM. The manual also says that if the VCM is replaced, the PROM module must be transferred to the new unit, and the EEPROM in the VCM (not the blue module) be programmed.

What's not shown in the photo of the blue plug-in module is that under that white circuit board are two large chips with the numbers "16127489 9502" on one and "16127490 9502" on the other. I should have mentioned that in my original post!

I am definitely new to the GM TBI computers, but is it possible that the blue module is in fact the MEM-CAL/PROM, or has the service manual labeled it incorrectly (which is certainly possible)?

[steveo]

why dont you take it apart and lets have a look?

[Six_Shooter]

There might be a PROM under that knock filter, and if there is you would use this MEMCAL adapter: http://www.moates.net/g4-adapter-for....html?cPath=64

It might not fit easily due to the physical design of the PCM. You would likely want to make a new cover for it, if that is the direction you go.

I've never heard of a "VCM", the only thing I can find that is remotely applicable when I search for VCM is "Variable Cylinder Management", which is a property of what some PCM/ECMs can do but not the PCM/ECM itself.

[delcowizzid]

looks like thats netres and knock filter and the tunes stored in the eeprom inside the ecu

[1project2many]

AFAIK you're stuck fast. The 95 W and Z underhood VCM's (Vehicle Control Module) are not supported by anyone. The W engine can be swapped to the 96+ black box. Could you do it with the Z engine? Possibly, but how well it can be tuned for the TBI is a big question.

Blue chip is the "knock module." Code and calibration is contained in flash. Could be somewhat OBDII compatible communications or could be old school 8192. System required special adapter with Tech1 and when I left dealership it still wouldn't talk to Tech2.


Practical answer, though not easy, is to move to in-cab control module 7427. Brave experimenters with a flare for challenges would convert to 96+ W engine pcm. The ghosts of Edmund Hillary and Roald Amundsen feel that reading the flash and disassembling the code is no big deal.

[kur4o]

This PCM is OBD1 flash based like LT1 pcm.
Can you provide detail pictures from inside of module to see what memory chip is used.

[ReadyXB]

There might be a PROM under that knock filter, and if there is you would use this MEMCAL adapter: http://www.moates.net/g4-adapter-for....html?cPath=64
It might not fit easily due to the physical design of the PCM. You would likely want to make a new cover for it, if that is the direction you go.

Thank you! I had already looked at the G4 but dismissed it (too quickly) because the computer shown in the photo was different than mine. But I believe the adapter will work. I just realized that I have some berg strips that are the same pitch as the module, so I may try and make my own as long as there's software out there for the computer.

I've never heard of a "VCM", the only thing I can find that is remotely applicable when I search for VCM is "Variable Cylinder Management", which is a property of what some PCM/ECMs can do but not the PCM/ECM itself.

"Vehicle Control Module". It has not only the engine management function but also ABS.

[delcowizzid]

there will be nothing to read off that memcal its just resistors and a knock filter

[ReadyXB]

there will be nothing to read off that memcal its just resistors and a knock filter

Pardon my ignorance as I am learning, but are you saying the entire PROM module is just a resistor and knock filter, or only the upper white board with legs?



Making reference again to the service manual, it identifies the PROM module as containing "...the operational software, backup fuel calibrations, and the up integrated knock sensor circuit." And, "The calibrations are stored in the VCM in the EEPROM".

So I see what everyone is talking about in regards to the knock sensor, but it seems that this removable module has more than just the knock function. I am guessing the 'operational software and backup fuel calibrations' are in the two chips under the knock board?



16127490 9502
16127489 9503

[ReadyXB]

This PCM is OBD1 flash based like LT1 pcm.
Can you provide detail pictures from inside of module to see what memory chip is used.

Yes! See previous post.

[ReadyXB]

AFAIK you're stuck fast. The 95 W and Z underhood VCM's (Vehicle Control Module) are not supported by anyone.

Do we know why? Is it just not as common and therefore not worth the development effort?

Blue chip is the "knock module." Code and calibration is contained in flash. Could be somewhat OBDII compatible communications or could be old school 8192. System required special adapter with Tech1 and when I left dealership it still wouldn't talk to Tech2.

I think we're on the same page for the knock function being in the module and calibration being in the VCM. But the emissions/diags manual says that the "operational software" is also in the PROM module, not the VCM. And it also confirms that the VCM contains four calibrations: engine, ABS, VSS buffer, and A/C. Does this sound familiar from your dealership days?

Practical answer, though not easy, is to move to in-cab control module 7427. Brave experimenters with a flare for challenges would convert to 96+ W engine pcm. The ghosts of Edmund Hillary and Roald Amundsen feel that reading the flash and disassembling the code is no big deal.

I will have to google those folks as I have no clue, lol, but I do have extensive assembly and firmware experience, of which reverse engineering is a big part. What I don't yet have is hardware such as flash readers/programmers/emulators, other than an ELM327 which helped confirm that my vehicle is not fully OBD II compliant. I'm also still getting up to speed on the lingo that everyone is using, such as "7427". I assume that is a portion of a part# for a complete PCM? The EFI Dictionary has been somewhat helpful but is missing terms such as "Broadcast Code" and "VCM".

I'm guess I'm just trying to understand what exactly I have since information on my specific VCM seems sparse. I would love to take advantage of any software and development already done - definitely not trying to re-invent the wheel. But I really appreciate everyone's comments and patience so far.

[ReadyXB]

Is "BSLL" the broadcast code?

[1project2many]

Do we know why? Is it just not as common and therefore not worth the development effort?

Possibly.

I think we're on the same page for the knock function being in the module and calibration being in the VCM. But the emissions/diags manual says that the "operational software" is also in the PROM module, not the VCM. And it also confirms that the VCM contains four calibrations: engine, ABS, VSS buffer, and A/C. Does this sound familiar from your dealership days?

Not all vehicles in '95 were equipped with underhood control modules. The calibration in the underhood module is changed via flash software. The two small chips in your photo contain "backup fuel" calibration data used by analog control circuits when the ecm cannot use the primary calibration.

I will have to google those folks as I have no clue, lol,

Explorers, trailblazers, pioneers.
Respectively...
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The EFI Dictionary has been somewhat helpful but is missing terms such as "Broadcast Code" and "VCM".

Broadcast Code (BCC)= alphanumeric code used correlate a calibration with an application and control module. BSLL is the original BCC for your VCM.
VCM = Vehicle Control Module

I'm guess I'm just trying to understand what exactly I have since information on my specific VCM seems sparse.

You have a one year, limited production, pre-obd control module which incorporates some design aspects found in later, more common control modules.

I would love to take advantage of any software and development already done - definitely not trying to re-invent the wheel.

That is the general approach for most. The '95 vcm may respond to OBDII programming protocols and software. It may respond to earlier protocols and software. It may respond to neither. I will try and remember to dig out the tiny bit of information I have at home regarding this module. Get no hopes up... there's very little info available. You could try using the OBDII programming software and cable available on this site (sorry, don't have a link to the thread) and see what the vcm responds with. You might try to see if Tunercat's flash tool for LT1 will communicate with the VCM. You could even contact some of the tuning software comany guys like TC and see if they have any clues they're willing to share.

There's plenty of patience here and even hope for some progress. But unfortunately there's little more available for help than what I can scrounge from OE service information.