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):

https://dl.dropboxusercontent.com/s/a6uxzbge3kpte74/IMG_1056m.jpg

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

https://dl.dropboxusercontent.com/s/uuvtwjsc70iwks8/IMG_1049m.jpg

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

https://dl.dropboxusercontent.com/s/j6t6gixcl17i3mh/DCP_1110m.jpg

https://dl.dropboxusercontent.com/s/cm46mnmsj76hpsr/DCP_1105m.jpg

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-9495-stuff-p-126.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-9495-stuff-p-126.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?

https://dl.dropboxusercontent.com/s/k5oskxlnbwydysf/0F8U9727m.jpg

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?

https://dl.dropboxusercontent.com/s/lxm6rc2k1mauwuh/0F8U9731m.jpg

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 (http://www.gearhead-efi.com/gm-ecm-pcm-conversion/efi-dictionary.html) 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?

https://dl.dropboxusercontent.com/s/uuvtwjsc70iwks8/IMG_1049m.jpg

[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...
first to ascend Everest and first to reach South Pole


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.

[kur4o]

I can`t see the pictures, looks like link is broken.

what you need to do is find memory chip, desolder the chip, solder socket, read the chip, post the bin file here, make disassembly, find calibration tables, make changes to bin, flash chip with edited bin, put chip in socket, go burn some tyres.

All OBD1 flash based PCM share similar design and I guess it might be very similar to lt1 and l32 PCMs, which are well understood.
You might contact TunerCat to see if they can add flash support from ALDL cable.

[kur4o]

I managed to open pictures.
Remove the whole black box with the label, and make pictures inside it at the main board.
Don`t search for removable Prom. Memory chip is soldered at the board and is not removable.

[ReadyXB]

I can`t see the pictures, looks like link is broken
I just double-checked the links and they are valid. Maybe the pics are too large?


what you need to do is find memory chip, desolder the chip, solder socket, read the chip, post the bin file here, make disassembly, find calibration tables, make changes to bin, flash chip with edited bin, put chip in socket, go burn some tyres.

Assuming you can see the photo, here is the VCM mainboard. There are two Intel AN28F512 CMOS Flash chips in a PLCC package (bottom-center).

https://dl.dropboxusercontent.com/s/xzj6rahrb1dy024/0F8U9718m.jpg

[kur4o]

That`s what you are looking for.(the intel chips)

You will need some chip programmer( willem is cheap and good quality) and two Plcc32 surface mount sockets.
Hope you have good soldering skills or know someone who can help.

Can you write down the numbers from the main processor.

The board looks like stripped version of l32 pcm.
Do you know if this VCM is capable of controlling Auto transmission.

[ReadyXB]

My soldering skills are good but I lack equipment. I'm on a very tight budget, so I need to exhaust all options and research before making the plunge to buy a USB programmer (ie, GQ-4X). Based on comments received so far, I will be sending a few emails. I've used Tunerpro RT quite a bit, so finding an XDF layout that already exists would be golden! Wishful thinking probably. I have an OTC Genisys scan tool that talks to the VCM just fine via the DLC, but of course it has no programming capability.

What I haven't yet found on the VCM board are any volatile chips. Per the manual, removing battery power to the VCM clears "learned" values; I assume this means values such as Long Term Fuel Trim (ie, block learn) and DTC's? I was just trying to locate a chip meeting that criteria. I suppose the clearing of learned values could be done by code based on some "power loss" bit?

[1project2many]

I have an OTC Genisys scan tool that talks to the VCM just fine via the DLC, but of course it has no programming capability.
Look for J2534 pass through programming. If available, if your VCM is supported, monitoring a programming event might be the key to upload/download. Also, if you have OBDII cable you could send unlock request and see what vcm sends for key.

This VCM will control trans, but his trans is manual.

[ReadyXB]

Do you know if this VCM is capable of controlling Auto transmission.
I am doubtful because a different computer was supposedly used for automatic trannys. Per the diags manual:

Control Module Application Chart:
93 PCM6:
- 2.2L (VIN 4) "S" Pickup, Automatic/Manual Transmission
- 4.3L (VIN Z) "S/T" Pickup, Automatic Transmission Only
- 4.3L (VIN W) "T" Utility AWD, Automatic Transmission Only

VCM-A
- 4.3L (VIN W) "S/T" Pickup and Utility, Automatic/Manual Transmission

VCM (what I have)
- 4.3L (VIN Z) "S/T" Pickup, Manual Transmission

Again, this info is coming from a 1995 S/T Truck "Driveability, Emissions, and Electrical Diagnosis Manual".

[ReadyXB]

Look for J2534 pass through programming. If available, if your VCM is supported, monitoring a programming event might be the key to upload/download. Also, if you have OBDII cable you could send unlock request and see what vcm sends for key.

Thanks. I'll look into the pass-through programming again. IIRC, the last time I checked (several years ago), those devices were subscription/fee based. But I definitely need to do new research.

[RobertISaar]

two 64KB flash PROMs and what looks like a 68000 model processor? that's going to be fun.

EDIT: D87M code does appear to be a 68332 controller.

[ReadyXB]

two 64KB flash PROMs and what looks like a 68000 model processor? that's going to be fun.

EDIT: D87M code does appear to be a 68332 controller.

https://dl.dropboxusercontent.com/s/avlpxf56pchtqzj/0F8U9719m.jpg

[RobertISaar]

yeah, that's definitely a 68332.... nothing I can help with, I can't read the code for those at all. if it were a 6800 derivative, that would be a different situation.

with the dual PROMs, I would imagine they have their own unique address spaces. if they were somehow interleaved..... that wouldn't be easily dealt with at all.

[kur4o]

I checked some diagrams. This VCM controls engine and ABS. There is different cal ids for engine abs and A/C like newer style controllers. Can you provide VIN number.

J2538 is only possible on OBD 2 vehicles so It`s not an option for you.

There is service bulletin #73-65-13 which gives some additional information.

[ReadyXB]

I checked some diagrams. This VCM controls engine and ABS. There is different cal ids for engine abs and A/C like newer style controllers. Can you provide VIN number.
Are you trying to determine if this VCM supports an automatic transmission?

1GCCS14Z6SKXXXXXX

[kur4o]

I want to see what calibrations will come up from VIN here
https://tis2web.service.gm.com/tis2web
(https://tis2web.service.gm.com/tis2web)
You can check and post result here if you don`t want to share full VIN.

I can`t wait to see what`s on this chips. Looks very interesting with this processor on board.
Please post bins here when you manage to read them.

I doubt it`s possible to control auto with this VCM.
They use the old style PCM on this engine with Auto transmission. It`s still an option to use this old PCM, but you will need new harness and ABS won`t work.

[1project2many]

J2538 is only possible on OBD 2 vehicles so It`s not an option for you.
I have non OBDII compliant vehicle in the fleet that are programmable using J2354 device.


Thanks. I'll look into the pass-through programming again. IIRC, the last time I checked (several years ago), those devices were subscription/fee based. But I definitely need to do new research.

Yes... fee based. But the amount of data you could obtain from one programming event is likely worth many hours of trial and error work. Tech2 / SPS is $55 for two days with appropriate hardware. Software available for download. I'd investigate.


I am doubtful because a different computer was supposedly used for automatic trannys. Per the diags manual:

Control Module Application Chart:
93 PCM6:
- 2.2L (VIN 4) "S" Pickup, Automatic/Manual Transmission
- 4.3L (VIN Z) "S/T" Pickup, Automatic Transmission Only
- 4.3L (VIN W) "T" Utility AWD, Automatic Transmission Only

VCM-A
- 4.3L (VIN W) "S/T" Pickup and Utility, Automatic/Manual Transmission

VCM (what I have)
- 4.3L (VIN Z) "S/T" Pickup, Manual Transmission

Again, this info is coming from a 1995 S/T Truck "Driveability, Emissions, and Electrical Diagnosis Manual".

I stand corrected.

[ReadyXB]

FYI: tc@tunercat.com replied to my email and said that they don't have anything for this VCM.

[1project2many]

FYI: tc@tunercat.com replied to my email and said that they don't have anything for this VCM.

That doesn't surprise me. But did they offer any hints about programming?

[ReadyXB]

That doesn't surprise me. But did they offer any hints about programming?
No, just the typical comment that it was "...an odd-ball VCM that was only used in that one year for the S10." But I appreciate their taking the time to reply.

I've got my eye on a ROM burner, and I'm also looking for a debugger that would work with the D87M microcontroller. It seems that GM did wire up the required debug traces out to that large, unpopulated 3x30 header at the bottom of the board.

[ReadyXB]

So the two flash ROMs definitely have an odd/even data storage going on. Should be loads of fun.

[kur4o]

Great.
I can make you a disassembly when you post the bins.
Do you know how to swap bytes.
I am sure one bin will contain abs logic and the other will be for engine calibration.

[ReadyXB]

Great.
I can make you a disassembly when you post the bins.

I will take you up on that!
Here are links for the two flash ROMs images. I called them ROM "A" (https://dl.dropboxusercontent.com/s/357xkymu6jul0i1/BSLL_AN28F512_A.bin) and ROM "B" (https://dl.dropboxusercontent.com/s/yinlnigzqh6huou/BSLL_AN28F512_B.bin).

I mentioned that my soldering skills were quite good. However, my "unsoldering" skills... not so much. I managed to rip a few traces off of the board during the process. Thankfully, my repairs were successful (well, my truck cranks and runs).
I also added ROM sockets in the hopes that we can identify key areas in these ROMs that apply to the base fuel map, DTC masks.
https://dl.dropboxusercontent.com/s/l1faai3jjbpjplj/IMG_1256m.jpg


Do you know how to swap bytes.
Yes, and I merged A+B into this ROM: BSLL_AN28F512_merged_A+B.bin (https://dl.dropboxusercontent.com/s/jmn2cle2s78xfgp/BSLL_AN28F512_merged_A%2BB.bin). A=even, B=odd. I chose A+B instead of B+A because I stumbled upon my VIN in the ROMs: half in ROM A and half in B! A+B made a correct VIN string. Of course it could be B+A, and if so, here is that file: BSLL_AN28F512_merged_B+A.bin (https://dl.dropboxusercontent.com/s/cxif67glpwi2l22/BSLL_AN28F512_merged_B%2BA.bin)


I am sure one bin will contain abs logic and the other will be for engine calibration.
Is it possible that not all areas of the ROMs are interpolated even/odd? I need to trace the address and data lines for both ROMs. I do know that all other pins on the ROMs are directly connected to each other, including CE/chip enable. Again, I think that only the data lines are separate between the ROMs but I need to check again. It was late and I was tired, lol.

[ReadyXB]

So my newly rebult engine is running quite well but I definitely need to tune a few areas. For example, I'm hoping to find a way to modify the BLM min value as it appears to never go below 108 for my idle cell (usually 0). The problem is, every time I re-enter the idle zone, Integrator re-starts at 128 and takes 17 seconds to decrease and stabilize at around 97/98 for a happy 14.7 closed loop idle. Very frustrating. Better yet would be the ability to modify the base fuel map so I can get BLM/Integrator back near 128.

I built an ALDL cable a few days ago. 8192 baud communication using Realterm. I now also have a bluetooth module working because I was getting too cold sitting in the truck outside for hours, lol. Now I can play on the couch.
So far, I have only been able to successfully request the Mode 1 datastream (F4,57,01,00,B4). Here is a sample reply:

F4 82 01 00 00 00 43 7C 03 00 CA 00 00 80 00 00 0B E3 04 1A 00 78 00 00 50 00 00 00 00 00 43 78 8A 88 00 50 00 00 00 00 00 00 25 CA 09 04 04 8C
Mode 10 also works. Requests for Mode 2 memory go unanswered. I would LOVE to snoop while a Tech 1/Tech 2 does a programming update and see all the magic, lol. Any pointers would be appreciated. My goal would be the ability to read/write a new tune over ALDL. Next best is to successfully disassemble the ROMs so I could reprogram them on my burner.

To be honest, I'm amazed this all still works. I rebuilt almost everything - engine and tranny, lol. It was my first time doing a manual transmission. Complete engine rebuild with all new do-dads and a 266HR Comp Cams camshaft. And, obviously, I even touched the computer.

[ReadyXB]

I'm making some good progress on decoding the ROM. I've located a few tables but definitely still have a ton to go.