'94 Jeep Cherokee Tuning

[jeeper]

I'm obviously new to this forum, and I'm not here because my jeep is boosted (it's not). I came here because i see some fair amounts of intelligence and inquisitive minds in the PCM tuning threads I've read. I've got a '94 Jeep Cherokee 4.0l 2WD w/AX15 trans. Just a few small mods like cold air intake, free flowing muffler, and 24lb 2nd gen bosch 4 hole injectors. I've stopped there because i feel the stock tuning isn't quite cutting it anymore and if i go further, i will see no gains due to lack of tuning. I've got 20-22mpg average. I'm shooting for more power and better mpg by way of PCM adjustments and underbody aerodynamic modifications.

The tuning information I'm searching for doesn't seem to be available on any Jeep forums. I have been doing lots of research on getting into the PCM's on these vehicles. As i understand, the SMEC and SBEC (I/II/III) from my jeep (SBEC II) and from most other Mopars of similar era are basically the same. I haven't gained much ground in interfacing with the PCM yet. I'm just starting with trying to get a basic connection to the PCM, and start to get responses. Then on to live data and tuning. I do know the baud is 7812.5 and 62.5k depending on what you're doing. I've started by purchasing an external serial-usb adapter so i can use my laptop in the vehicle. I know i'm dealing with SCI and that its a motorola setup, but thats all the real definite info i have. I also have a USB ELM327 for live data and DTC's and hopefully tuning some of my friends OBD-II cars.

I'm actually wanting to learn how the maps work and how to actually interface with the PCM down to the OBD commands, the AT commands, actual code, etc. I don't just want to go fast and want it now. I'm here to actually learn something.

[Vigo]

User: ShelGame http://www.turbo-mopar.com/forums/me...p?141-ShelGame is the guy to go to for stuff like this, and i believe he expressed interest in tuning 4.0 jeeps in the past. Depending on how far he has gotten with that particular style of pcm, what you're trying to do could be extremely tedious to learn.

I'm normally not the guy to suggest taking the easy way out on a laudable goal like learning how to tune your own ECM, but i have to wonder if most of the adjustments you would like to make would be possible with an over-the-counter 'piggyback' computer system altering the signals your factory ECM reads. What's your take on that?

[jeeper]

User: ShelGame http://www.turbo-mopar.com/forums/me...p?141-ShelGame is the guy to go to for stuff like this, and i believe he expressed interest in tuning 4.0 jeeps in the past. Depending on how far he has gotten with that particular style of pcm, what you're trying to do could be extremely tedious to learn.

I have indeed read some of shelgame's stuff on here and what i read is what made me join here. i actually would be willing to assist him if needed.

I'm normally not the guy to suggest taking the easy way out on a laudable goal like learning how to tune your own ECM, but i have to wonder if most of the adjustments you would like to make would be possible with an over-the-counter 'piggyback' computer system altering the signals your factory ECM reads. What's your take on that?[/QUOTE]

I do know of the piggy back systems as well but I don't want to shell out the cash and honestly, it wouldn't be as fun to me to just slap it on there and tune away. Changing maps seems like it'd be a blast to me. The challenge is the fun part. I totally understand it won't be the easiest task in the world to disassemble the PCM. I feel like i might be more crazy than a lot of DIY'ers out there but its fine with me.

[shackwrrr]

The hardware is already done and in use by some people here. Some of our cars came with an SBECII just like your jeep. Shelgame makes a chip that you solder in place of the factory eeprom, you then use an FTDI USB to serial cable to interface with the ecu with MPtune. The problem with tuning for the jeep is the code which to my knowledge shelgame hasn't done any work on disassembling. I am very interested in this as I have a 93 grand Cherokee that I would like to make tweaks to but I don't want to take away from the time shelgame spends on the turbo codes.

[ShelGame]

I have a couple of Jeep cals for the SBECII. I've done some work to dis-assemble them. But, it looks like Jeep must have used their own staff to write the code. nothing is the same as the car cals except for some of the utility routines (2D/3D lookups, 16-bit math, etc.). So, finding fuel and spark tables has been difficult.

[jeeper]

I have a couple of Jeep cals for the SBECII. I've done some work to dis-assemble them. But, it looks like Jeep must have used their own staff to write the code. nothing is the same as the car cals except for some of the utility routines (2D/3D lookups, 16-bit math, etc.). So, finding fuel and spark tables has been difficult.

Hmm. Not quite what i was expecting to hear. Nice to hear that someone has some interest and has at least started with them. I wonder if the difference between them being 4 cylinder and 6 cylinder has anything to do with it? I dont know much about the 2.2 and 2.5 you guys work with as far as EFI goes. The only one i worked on was an 87 dakota with lean burn. So i have no idea how the EFI is set up on those. The jeep is very simply set up. Just a small handful of sensors. If your 2.2/.5 has another setup that would explain the difference in coding. A different set of inputs.

[ShelGame]

Hmm. Not quite what i was expecting to hear. Nice to hear that someone has some interest and has at least started with them. I wonder if the difference between them being 4 cylinder and 6 cylinder has anything to do with it? I dont know much about the 2.2 and 2.5 you guys work with as far as EFI goes. The only one i worked on was an 87 dakota with lean burn. So i have no idea how the EFI is set up on those. The jeep is very simply set up. Just a small handful of sensors. If your 2.2/.5 has another setup that would explain the difference in coding. A different set of inputs.

No, that's the funny part - the sensors and fuel/spark systems are very similar. That's part of the reason it's so confusing as to why it's so different. The Jeep cals have some similarities to the V6 and V8 truck cals.

I've seen the same thing even among turbo cars. The Mexican cals were completely different from the US cals until '92. In '92 they were the same code. Even the Masi and TIII cals (the early DOHC engines) were different from the 8v engines.

[jeeper]

Hmm. Kinda makes sense that it'd be similar to the truck stuff considering its somewhat of a truck anyway. But why wouldn't they keep one code format across the board for simplicity in the programming department. It would make more sense to me, but that's just me. What 4.0 jeep cals do you have?

[ShelGame]

The only Jeep cal I have is actually the '95 4.0L 4x4 5-speed cal. I thought I had a 2.5 around here somewhere...

[jeeper]

Thats probably going to be almost identical to mine. (94 4.0l 5-speed) can you send it to me via pm or something? what do you use to view it? i'm wanting to at least see what it all looks like and send a copy to a professional software developer friend of mine. he codes for fun and knows just about any programming language under the sun i wanna see what he says about it.

[ShelGame]

Thats probably going to be almost identical to mine. (94 4.0l 5-speed) can you send it to me via pm or something? what do you use to view it? i'm wanting to at least see what it all looks like and send a copy to a professional software developer friend of mine. he codes for fun and knows just about any programming language under the sun i wanna see what he says about it.

There's not much to look at. Tables, etc. are not defined. But, we use MP Tune to edit cals once we have at least a table definition setup for them.

[jeeper]

what is the raw format? I want to learn all this on a low level first. I understand that me asking for this stuff is like diving head first into an empty swimming pool, but I want to at least get a hold of it and possibly try to come up with definitions.

[ShelGame]

what is the raw format? I want to learn all this on a low level first. I understand that me asking for this stuff is like diving head first into an empty swimming pool, but I want to at least get a hold of it and possibly try to come up with definitions.

Binary is the raw format. The table file is a definition file that tells the editor what the bytes in the tables represent (and where the tables are).

[jeeper]

Can you send me the 4.0 cal you have? I actually have a little, tiny, bit of experience with reading some binary from a class i took in school. And i can learn to read hex if it'd help. I have an a+ certification text book with sections on how to read both of those. I mean we are only talking like a 32 or 64k file right?

[ShelGame]

Can you send me the 4.0 cal you have? I actually have a little, tiny, bit of experience with reading some binary from a class i took in school. And i can learn to read hex if it'd help. I have an a+ certification text book with sections on how to read both of those. I mean we are only talking like a 32 or 64k file right?

Yeah. 'just' 32k...

I found the other Jeep files I have; and a PN list for the ECU's...

[jeeper]

32k sounds like nothing nowadays but it still is 256,000 individual bits. what program do you prefer to use for viewing the .bin's directly?

[ShelGame]

I use a hex editor...

[jeeper]

Ok. I've used a re-assembler and i've got the .asm file now. I see that my next step is naturally going to be learning the 68k command set. IIRC, the cpu in these is a motorola 68HC11?

[ShelGame]

Ok. I've used a re-assembler and i've got the .asm file now. I see that my next step is naturally going to be learning the 68k command set. IIRC, the cpu in these is a motorola 68HC11?

How did you get it to an .asm without knowing what the processor was? The opcodes are all processor-specific. It is a 68HC11. Chrysler used them in everything up until ~'96...

[jeeper]

I knew it was 68hc11. I was just double checking with you. I am familiar with that processor family from my two 68000 Macs. I used a 68k reassembler