PCM Reflashing/Programming

[Alexia]

This will cover mostly 1997-2001 XJ models.

There is a person out there that claims he can reprogram 1997-2001 Cherokee PCMs for stroker applications and boosted applications using SCT hand held programmers. Boosted would still external hardware for additional help since the PCM was not designed for boosted applications. This reprogamming and reflashing is done over the CCD bus. The Chrysler DRBIII along with newer Chrysler tools and SCT programmers have the capability to do this over the data link connector.(ODBII port)

The problem is that CCD is Chrysler proprietary and requires reverse engineering to understand. That means everyone that has reversed it to the point of being able to reflash firmware is either keeping it to themselves or started a company to sell programming tools. That leaves us with the situation of having to pay hundreds of dollars to tuners that have paid thousands to a company to be allowed to use their tools.

Please add any additional information you may have on any of this!

CCD Bus Information:
http://articles.mopar1973man.com/general-cummins/34-engine-system/81-ccd-data-bus

Some rambling history of Chrysler scan tools:
http://www.ebay.com/gds/Chrysler-Starscan-StarMobile-wiTECH-amp-DRB-III/10000000014811396/g.html

Juha has some schematics on harvesting CCD IC chips to build a display unit. He also has information on the Chrysler PCI bus for newer Jeep vehicles on his home page.
http://www.kolumbus.fi/juha.niinikoski/CCD_bus/ccd_display.htm
http://www.kolumbus.fi/juha.niinikoski/index.htm

Q: What about CAN bus?
A: 1997-2001 XJ PCMs do not have it.

Q: What about SCI/ISO 9141 bus?
A: 1997-2001 XJ PCMs have it, but do not use it for flashing or programming as far as I can tell.

 

[sidewaysstarion]

I think I know a guy who knows a guy that knows a guy that can reflash a jtec or two.

As for using the SCT tuning package to build a boosted calibration, three words, DON'T DO IT!!!:explosion The way most guys do it is they replace the stock 1 bar map sensor with a 2 bar map sensor and then remap the fuel and timing for the new map sensor voltages, but there are alot of other tweaks that needs to be done to pull this off and the SCT software doesn't have access to those areas of the ecu.

 

[Alexia]

I think I know a guy who knows a guy that knows a guy that can reflash a jtec or two.

As for using the SCT tuning package to build a boosted calibration, three words, DON'T DO IT!!!:explosion The way most guys do it is they replace the stock 1 bar map sensor with a 2 bar map sensor and then remap the fuel and timing for the new map sensor voltages, but there are alot of other tweaks that needs to be done to pull this off and the SCT software doesn't have access to those areas of the ecu.

I was purposely not naming any specific people to come off as advertising and keep it focused on the PCM aspect.

That is why I said "with external hardware" for a boosted setup. Program the PCM to be happier with the engine in a naturally aspirated state and make it easier for the external hardware to make changes.

 

[sidewaysstarion]

Well here's a bit of info, the flashing routines run over SCI and not CCD

 

[O-Gauge Steamer]

^^You bet there is.

Like the timing has to be pulled back under boost.

If there was not a vehicle in the product line that came with Forced Induction as an Option, then there will not be the programming available in the PCM to handle the sensor input correctly. As far as I know, nothing from MOPAR came with forced induction during these years.

At issue is the that Chrysler, in their infinite wisdom, went in a direction that nearly no one understands why.

I have looked at the SCT website. They do not admit that their programmer will work with any Jeep... Should as the PCMs are pretty close to the same. I would feel confident if my Heep was listed as a supported vehicle.

Given the age of our electronics and the unavailability of some of the components (like the main connector on the PCM) I am a bit gun shy of letting it out of my grubby little mitts.

So easy to blow them up. Plus, if it is wrong, it is another trip back to the programmer. My Heep is a DD. Sort of need the thing running...

Plus, it defeats the entire purpose of being able to tune it yourself for your particular application.

If only the DRBIII tools weren't so bloody expensive. Even on eBay they are very spendy running between $2k and $3k as of today (7/21/13). A tad out of my reach. Plus, isn't the tool itself limited?

B&G Performance are big into MOPAR PCM flash and even they say to "send it in"

 

[Alexia]

Well here's a bit of info, the flashing routines run over SCI and not CCD

I should know better than to trust the Factory Service Manual after all the errors in that thing. *Shakes fist in the air.*

 

[Alexia]

Given the age of our electronics and the unavailability of some of the components (like the main connector on the PCM) I am a bit gun shy of letting it out of my grubby little mitts.

I wish AEM could still had a supplier so we could the patch harness still. If I had a busted XJ PCM I would gladly open one up to make a patch harness.

If only the DRBIII tools weren't so bloody expensive. Even on eBay they are very spendy running between $2k and $3k as of today (7/21/13). A tad out of my reach. Plus, isn't the tool itself limited?

B&G Performance are big into MOPAR PCM flash and even they say to "send it in"

Yeah, the DRBIII is limited only for the reason that it required constant updates and only really supported what the factory/service technicians needed to do in a typical setting.

 

[sidewaysstarion]

I wish AEM could still had a supplier so we could the patch harness still. If I had a busted XJ PCM I would gladly open one up to make a patch harness.



Yeah, the DRBIII is limited only for the reason that it required constant updates and only really supported what the factory/service technicians needed to do in a typical setting.

Like ECU flash updates... :kissyou:

Also Dave over at B&G does real ecu tuning, he doesn't use the SCT suite to build "tunes", he is one of 2 people in the US that I know of that knows how to properly tune a Jtec/sbec ecu.

 

[Alexia]

Like ECU flash updates... :kissyou:

Right, but only updates provided by Chrysler. If we had the files on disk and a DRBIII/Starscan we could get into some EXTREME hex editing fun with them before flashing them.

 

[sidewaysstarion]

Right, but only updates provided by Chrysler. If we had the files on disk and a DRBIII/Starscan we could get into some EXTREME hex editing fun with them before flashing them.

Well... the issue with that is
A. The files are encrypted.
B. The files have checksums both on the files themselves which the DRB checks and the Calibration has its own checksum which the ECU verifies.
C. Even if you managed to decrypt the files, how would you know what to change? do you have a Hex map? I can tell you the code is not commented in any way shape or form and is raw machine code.

 

[Alexia]

Well... the issue with that is
A. The files are encrypted.
B. The files have checksums both on the files themselves which the DRB checks and the Calibration has its own checksum which the ECU verifies.
C. Even if you managed to decrypt the files, how would you know what to change? do you have a Hex map? I can tell you the code is not commented in any way shape or form and is raw machine code.

A.) If the files are encrypted then the decryption key is likely on the DRBIII/Starscan device. I doubt a 1997 PCM would have enough processing power and memory to decrypt the firmware every time it needs to boot.

B.) Find where the checksum is stored and update it.

C.) That is the fun part. The first step that makes the process a bit easier is diff'ing an older and newer revision firmware. The patch notes for that firmware will then give clues to what the differences are.

 

[CobraMarty]

Alexia, do you have or need a 98+ ECU to test, take apart, investigate?

 

[sidewaysstarion]

Alexia, do you have or need a 98+ ECU to test, take apart, investigate?

98 is Jtec, 99-01 is Jtec+ which are different ECUs.

 

[Alexia]

Alexia, do you have or need a 98+ ECU to test, take apart, investigate?

I can grab one at the local LKQ for reasonably cheap.

I am reading a bunch of tuning JTEC style PCMs from the Dodge crowd. Assuming that the Jeep JTEC PCMs are similar enough it should be possible to to mess with their ROM chips as well.

 

[O-Gauge Steamer]

Actually...

Pursuant to what I have been informed, all of the PCMs for a given year Chrysler product use the same hardware in the PCM... It is the programming that separates the Rams from the Jeeps.

As I understand it, even the Viper uses the same PCM.

Which makes sense. As a manufacturer, why on earth would you want to build different hardware for the different product lines. Much more cost effective to change the code in the box and slap a sticker on it with the part number...

Of course, I could have it wrong.

 

[Alexia]

Actually...

Pursuant to what I have been informed, all of the PCMs for a given year Chrysler product use the same hardware in the PCM... It is the programming that separates the Rams from the Jeeps.

As I understand it, even the Viper uses the same PCM.

Which makes sense. As a manufacturer, why on earth would you want to build different hardware for the different product lines. Much more cost effective to change the code in the box and slap a sticker on it with the part number...

Of course, I could have it wrong.

That is essentially correct with some hardware variations such as six versus eight cylinder versions. Personally I would design a version that has all of the necessary injector and coil drivers for up to the most cylinders needed and just turn off the ones not being used in the software.

 

[streetxj]

Hey. Don't forget about us 96' jeep 4.0 OBD-2 guys. We don't like being left-out..

 

[O-Gauge Steamer]

That is essentially correct with some hardware variations such as six versus eight cylinder versions. Personally I would design a version that has all of the necessary injector and coil drivers for up to the most cylinders needed and just turn off the ones not being used in the software.

Again, As I understand it, the drivers are present in the PCM. Ever look to see just how many empty cavities are in the connectors? Keep in mind that the PCM for COP is different at the hardware level as well as the software than for the distributor models. To confirm both a V-8 and one of our PCMs would have to be cracked open and a component count made.

Seems a silly thing to do just to satisfy the curiosity.

Still, all this does not help us find a way to plug into the Com Port and flash the PCM does it?

I have a few things I would like to change including the shift point into OD at WOT. Need to move the point down. No need, want nor desire to have it shift at or about the 4,800rpm point. Especially if I get the rev limit moved down to about this point.

 

[O-Gauge Steamer]

Hey. Don't forget about us 96' jeep 4.0 OBD-2 guys. We don't like being left-out..

That is all right, we will hold a prayer meeting for you guys...

No, really...

As I understand it, your PCM is the same as well. All of the pre-COP PCMs are the same at the hardware level.

Coil
On
Plug

Fir those wondering.

 

[streetxj]

That is all right, we will hold a prayer meeting for you guys...

No, really...

As I understand it, your PCM is the same as well. All of the pre-COP PCMs are the same at the hardware level.

Coil
On
Plug

Fir those wondering.

lol In what year did the transmission started sharing the main ECU with the engine? In my 96', if there was something not working, like the TCC solenoid for example, it would not trigger the CEL.