'94 Jeep Cherokee Tuning

[jeeper]

What typically does one do to come up with a definition file? Is it going to involve me actually figuring out what the contents of the table are?

[jeeper]

It's been a minute since I've been on here, but i haven't given up. I've been busy with college finals and whatnot. I have done some work in disassembling this mess of numbers. This is quite difficult actually. I'm using dhc11 as my disassembler now. I'm making some decent progress familiarizing myself with the registers and command set. I find it easier to write the sections of code in question down on paper and make notes that way. Now that i've got my feet wet so to speak, can i have a to-do list? It's kinda difficult for me to get anywhere without any short term goals. It just makes it look like a bunch of code with no meaning. I know i need to come up with definitions at the end of this but I'm here and that's there and i have no idea whats in between.

[ShelGame]

Maybe this will help. I wrote my own dis-assembler (actually, modified someone else's work). This has some Chrysler-specific structure dis-assembly (2D and 3D tables, for example). I included the symbol file, and batch files, etc.

Basically, I edit the symbol file, add definitions, etc. then run the Jeep_all.bat file. It will disassemble the 3 Jeep bins here using the same definitions, and re-write the 3 .asm's.

I read thru the .asm, compare it to a known .asm (from a car cal, for example - you can DL them here) and update the symbol.txt file, save it, and run the .bat again; lather, rinse, repeat, etc.

[jeeper]

I feel like by the time i'm done with this whole deal, i'll be so familiarized with the obd-1 jeep system that i may build a custom intake manifold for my Datsun's EFI setup and just using the sensors, harness, and SBEC from a 2.5 Jeep. crank and cam sensor placement would be the major impediment to completion, though. Totally off topic, but i guess you could call that the sneak peek into my plans for my actual project car. I'll just have a spare SBEC for my jeep for tuning purposes, since its my DD.

[Vigo]

There is no 'cam sensor' per se. The pickup in the distributor serves that purpose.

[jeeper]

i understand that. the on/off telling the pcm what revolution the crank is on. like 1-5-3 or 6-2-4. or 1-3 or 4-2 on the datsun engine. but it still may be a task to get it to actually function properly.

[jeeper]

I had a wrench thrown into my gears last Thursday. The PCM has failed. Sounds crazy? Well i tested it using the TC-2A diagnostic flowchart that i got from the FSM. I was coasting down a hill and lost my tachometer and speedo simultaneously. Since i was engine braking down hill, i didnt notice it stall. But of course it was just being dragge along by the Jeep. I pulled over and did the 'ol key trick to find the sequence 12,11,55. It's not so uncommon on jeeps, so i swapped out the sensor actually twice with known good sensors. Then i finally found a relevant flowchart in alldata. Tested it according to the chart and a technicians youtube video using similar techniques. No response from the ECU when i switched CPS signal on and off (touching signal line to the sensor ground line, and listen for ASD relay to kick). Switched out relays, tested fuses, resistances, and voltages and grounds. Once you reach the last step in the flowchart my result ends in "replace PCM". Literally everything checks out fine except the persistent no spark and code 11 even after clearing codes. Not to mention the incorrect code 21 for a failed, brand new NTK O2 sensor, and the code 24 for the TPS. The 889 PCM is very inexpensive, though. With my O'reilly employee discount its a staggering $73. I will run through the flow chart once again after electrical class on Monday to make sure I didn't overlook anything and then I'm putting the PCM in. One day i'll get to tune it.

[jeeper]

I've added some more stuff to my symbols file, now i'm trying to figure out how to make it into a table file so i can use it in mptune. and does it require me to add it to something under the master templates menu option?

[jeeper]

Well, just to say i loaded a jeep cal into mptune, i borrowed (kinda cheated) a .mpt file to see if there was any parameters that matched up between for instance, a tIII and my jeep. i can tell which ones blatantly dont, by the jumble of blue garbage. I'm feeling my way around cal central more than anything right now. just digging around in menus and such. I did add a 4.0 manual, 1994 Cherokee, and Jeep SBECII menu options under cal info. Now i'm on to converting the mildly updated version of the symbols.txt file into a useable .mpt file.

[Vigo]

Sounds like progress. Tedious, as expected. Eventually others could certainly benefit from the work you're putting in. Thanks for keeping the thread updated with your progress!

[jeeper]

It is quite tedious. I am really excited to see what others will be able to do once the door to the 4.0 is open. They have a lot of untapped potential, even in N/A form. I thought it was pitiful to see other jeep owners on other forums doing things that are more difficult than this to get power. like v8 swaps and swapping GM ECU's and things like that. I think the software route is more interesting and more original. BTW, i was able to use a DRBIII on my jeep at school yesterday. That was interesting. I finally got to see some live data on this thing. With the 24lb/hr Bosch Gen-III injectors, my LTFT is a whopping -19%!! I have noticed on my AFR gauge, that any time i move the throttle, it pegs out on the rich side and then starts to adapt back to normal levels. IIRC, ShelGame referred to this in another thread as a transient fueling problem? I feel like once the fuel map alone is dialed in correctly, I'll see some noticeable improvement in throttle response, MPG, and overall smoothness of the engine as compared to factory. They actually have a nice "spray cloud" as i call it. Very nice atomization from these. I'm also in an emissions county, so i'm curious to see how the sniff test turns out when i'm on the rollers (since i'm OBD-1).

[Vigo]

Well, as far as i know the computer will have an acceleration enrichment function that can be modified once you find it. It serves the same purpose as an accelerator pump on a carburetor, to keep the engine running smoothly until the computer is able to get feedback on what the new fueling requirements are. Shelgame might be able to give you some tips on where to find that. I certainly don't know enough about it to help with specifics.

But i think you're right about untapped potential. There is a website out there belonging to a guy who got his n/a 4.0 into the 14s in the 1/4 mile with bolt-on mods and some very crude fuel tuning done by altering the reference voltage to the map sensor. Obviously a better method would give even better results.

[jeeper]

On a 93 T3, its the first line. What is labeled "AccPumpScaleDeltaTPSFromCoolantTemp" is what determines the pulse width that the computer uses in this instance. And i also know that the computer goes open loop after a certain throttle position as well. I can tell when it does it on mine based off of the fact that the AFR gauge stops sweeping and goes in the middle of the rich side and stays. And I have a MAP sensor adjuster on my desk that was waiting to be built. Then i read some more and realized that it only worked during the WOT enrichment stage. I thought i could scale everything down. But that's not the case.

[sev80]

I know it's been a few years since this thread was updated, but curious if this ever got figured out? Would LOVE to be able to tune my Jeep 4.0

[wowzer]

i'm working hard on getting the jeep 781 cal setup for mptune. i've identified quite a few of the tables and will put up a version later this week for all to review. basically all i've done is try to compare the existing disassembly to other cals, primarily the t-t3. unfortunately alot of the stuff does not carry over. rob L is the best one to determine really what the code is actually doing and being able to ID the tables/routines.

[UglyBoost91]

Hi All,

Just wanted to say that I'm very, VERY interested in all the great working being put into the OBD1 SBEC code. I have not been on the forum in a few years (used to own a couple TDs) but I do own a Cherokee and Comanche and found this post after extensive google searching

While my code knowledge is limited (I've built mega-squirts and tuned
GM OBD1 cars with Moates, but that's it; not extensive actual diving into the code) I would be happy to lend a hand wherever needed. I actually have a few different 4.0 ECUs and a 2.5L on a shelf, if anyone would like the reads from their PROMS.

Dumb question, but what are you using to read / write? Would one need to solder in a ZIF socket such as what I've had to do with the GM ECUs and then use an EEPROM? Is there any weird voltages on the Chrysler PROMs such that my Moates Ostrich would not be able to read a factory PROM?

Thanks and looking forward to anyone's progress!

Eric

[wowzer]

here is a first attempt at an updated 781 cal for the 4.0 jeep. there are a LOT of tables/code i have not figured out - hoping some of the more experienced cal guys can help ID them. let me know what you can figure out and i'll update the base cal.

[sev80]

here is a first attempt at an updated 781 cal for the 4.0 jeep. there are a LOT of tables/code i have not figured out - hoping some of the more experienced cal guys can help ID them. let me know what you can figure out and i'll update the base cal.

wow! nice job on getting this together!

[wowzer]

i've been plodding through it some more. i'll do another update this week.

[wowzer]

another update. added a few more tables and updated alot of the underlying code with labels. i probably won't do another update for a couple weeks. i need to firm up the row/column headings for the 3d tables as well as start looking in depth at what the code is actually doing to try to name alot of the other undefined tables. also, a large share of the units and ranges are not accurate.