Jeep SBEC PCM tuning (91-95)

a_kelley

a_kelley

mechanical fixer
Joined
Jan 26, 2010
Location
Rutherfordton
Well, I kind of started on deciphering the 91-95 Jeep SBEC computer.. just curious, is there any interest in people getting their computer tuned for strokers or forced aspiration? It'll happen for myself either way, but was thinking of offering it as a service if there was any interest. As far as I know, there may only be one other individual/company offering sbec tuning. Special hardware and a logger is required to tune them, as well as minor surgery to the SBEC.
 
Last edited:
That's the software I'm using. I'm 95% done with creating the tune file. I've got background in ECE so it's not a monumental task to me. Thinking of just socketing the pcm instead of flash in place for simplicity. I will have to go to a 2 bar map and size up injectors, possibly tweak spark tables, so I'll know that I got it all identified right. Contemplating making a bench set up but probably isn't worth the time. It's also awesome that mptune can autotune from a wide band o2 data log.
 
I am absolutely interested in getting my ZJ tuned! Please keep in touch, I want to see how progress is going.



NOTE: EDIT FROM 2024: Before a reader goes 13 pages into this thread, Akelly and I got pretty far into this project and then eventually Akelly moved on so we never finished it. We got as far as building a DOS based toolset to flash the ST based late 94-95 SBECIIs and Akelly wrote some rudimentary tools to read and modify fueling/spark tables for SBECs but it was very alpha stage and after that the project kind of stopped. I ended up paying Chris Jensen to write me a tune, so I stopped my efforts on this project as I dont have enough deep knowledge in assembly language to continue Akelley's work.

I have some of the code and work we did still but Akelley has moved on and sold all his jeep stuff. There's some good contributions towards the last 2-3 pages of this thread with schematics and other stuff, but any work or mention of work you find in these pages were never completed. I thought I'd post a little note before anyone else who discovers this gets 13 pages in and get disappointed. :)

If YOU have the technical prowess and want to pick up where we left off from, I'm happy to work together.
 
Last edited:
I have a 94 grand Cherokee.

Done a couple mods to it like 704 injectors, WJ manifold, 62mm tb and 2.5" exhaust
 
Any updates?
 
Well, wowzer over on turbomopar has been working on his version of the 781 cal, but I got the fuel and spark tables mapped out in my cal. Load it in MPTune and you can look it over. Another PCM would be easy enough to make a cal for since this one is about finished (at least as far as compiling back to the original, tune is dependent on the vehicle)

'94 Jeep Cherokee Tuning

my tune is attached, can open them in MPTune. A FTDI cable is needed as well as adding a pin to the ECM connector to download the bin. To reprogram, thje ECM has to be "socketed" or replaced with a flash chip. I'll post up more after I have mounted my charger and flashed my own successfully.
MPTune - MPSuite
 

Attachments

  • 781_ak.zip
    215.5 KB · Views: 770
Tried opening in MPTune and it throws error on youe tpl file. Doesnt seem to want to open..
 
Sweet. Taking a look through your cal. Awesome job. I cant pretend I know what Im doing but I'm really curious and trying to learn

Im looking at the spark table. I see 1A 1B and 2, is this for closed loop, open loop and WOT?

Also I see RPM, PSI (map I assume) and "Units Factor" what's the units factr? The number seem to big too be anything with crank angle.
 
for kicks, i complied and burned your cal to a chip and tried it in my truck. The fuel pump didnt prime and the ECU wasnt responding to my DRB II.


I wasnt expecting it to work, but is your complete enough for a compile/flash?
 
How can I help? I've been running a striker for years with "cheating" the tune. Just bigger injectors and more fuel psi, but I'd love to tune it some.

I'm in. I have that which is a 90 converted to 92 stuff, and then I have another bone stock 92 4.0. Both yj.
 
I have a dummy assembler listing on mine, didn't finish it yet, that was to see all the tables that were in the ROM. The ASM needs all the hex codes from the bin listing removed, was going to write a Perl script to strip it out instead of doing it manually but just got swamped with work. 40 continuous work hours in 2 days is not my definition of fun.

@Mac5005 Yes this will apply to wrangler ecms as well. (Perhaps minor to tweaking if your ECM # differs but I'm not sure if there are hardware differences or just code, I know any 4.0 sbec ECM will run any sbec 4.0 (mine is auto trans with manual ECM, no issues except cruise control kicking out on shifts))

Not sure how much power is left on the table on a stock motor in the stock tune.. lacking a knock sensor is a problem for bringing the timing tight in, more on the stroker than stock I would imagine depending on compression ratio.
 
a_kelley said:
I have a dummy assembler listing on mine, didn't finish it yet, that was to see all the tables that were in the ROM. The ASM needs all the hex codes from the bin listing removed, was going to write a Perl script to strip it out instead of doing it manually but just got swamped with work. 40 continuous work hours in 2 days is not my definition of fun.

@Mac5005 Yes this will apply to wrangler ecms as well. (Perhaps minor to tweaking if your ECM # differs but I'm not sure if there are hardware differences or just code, I know any 4.0 sbec ECM will run any sbec 4.0 (mine is auto trans with manual ECM, no issues except cruise control kicking out on shifts))

Not sure how much power is left on the table on a stock motor in the stock tune.. lacking a knock sensor is a problem for bringing the timing tight in, more on the stroker than stock I would imagine depending on compression ratio.
Click to expand...

Wish I could copy my base factory tune to write to micro or mega squirt so I could add a knock sensor and swap to mega or micro squirt for full tuning.

Subscribed to follow along.
 
hey any updates on compiling/bench testing the cal? Curious how modified your 4.0 is? Do you have a stroker?
 
When I get there, one will be supercharged stock motor and my daily will get a stroker. I'm about a month out from building the stroker and getting anywhere on a bench setup.
 
I'd LOVE to supercharge mine. Alas, stupid california smog laws would prevent me from doing so..Maybe one day when they exempt obd-1
 
Anything ever come of this? Were you able to put together the bench setup and test/tune?

I bought a street tune for my ZJ from Chris Jensen,been pretty happy with it.
 
Back from the dead!!

Me being me, I started to create a usb interface for sci, but need to order some chips because discrete bjt transistors were screwing up signal timing.. so I rewired it to a com port and lo and behold... I dumped a 360 rom using code from the bootloader reworked. Anyone interested in the bin can get in touch with me and I'll get it to them. Also have another ecm but it's still in my Jeep. Next step is to flash my flashable ECU. I'd love to use my interface instead of the com port because 9600 baud is pretty slow. Wrote a simple wrapper to upload the command bins and dump and flash. Idea was to first get the rom dumped, then uploaded to the flashable ECU and put it in the Jeep and verify operation. Then move on to injector resize and map rescale for the 2bar td map sensor. (While still running na) then add boost. So I'm closer to my bench setup.
 
Last edited:
very nice!!! thinking about stroking my ZJ to a 4.6... I barely drive it these days though.

Really digging the tune I got, totally changed how the thing drives. Only problem is there's something wrong with the ECU I socketed, every once in a while it cuts out and stalls. Going to possibly socket another. I have the newer, flashable ecus but obviously no way to flash.
 
There is a way to flash the newer stock flashable units. It takes 21v and a special interface to trigger the programming voltage when required. Not sure if it was completely developed in mptune or not, being that they are somewhat rare compared to the non flash units. I could create the interface for those but I would need one of the ECU to test it out. Mine is socketed with a eeprom, next one I'll solder right into the board.
 
Rob Lloyd actually developed a device to do the flashing, he was selling a few on the neon forums...I tried to get one, but he said it only works on Neon SBECs. He said his device would need additional work to work with flashing jeep SBEC's. Didnt seem like he was to interested in spending the time on getting that part working on Jeep SBEC's since he's retiring.

Neon PCM Reprogramming - Page 37 - www.neons.org

Seems like all work related to Jeep stuff on turbo mopar died out, too bad. I felt like we had good momentum.. Glad to hear youre still at it! It would be awesome to be able to get a fully mapped jeep cal. Believe it or not, for Grand Cherokees, a majority of the SBEC's I've come across are flashable, only the really early ones are not. I'd be happy to lend you my flashable one if you wanted to use it as a guinea pig. They're also a dime a dozen at my local junkyard.
 
Last edited:
sev80 said:
Rob Lloyd actually developed a device to do the flashing, he was selling a few on the neon forums...I tried to get one, but he said it only works on Neon SBECs. He said his device would need additional work to work with flashing jeep SBEC's. Didnt seem like he was to interested in spending the time on getting that part working on Jeep SBEC's since he's retiring.

Neon PCM Reprogramming - Page 37 - www.neons.org

Seems like all work related to Jeep stuff on turbo mopar died out, too bad. I felt like we had good momentum.. Glad to hear youre still at it! It would be awesome to be able to get a fully mapped jeep cal. Believe it or not, for Grand Cherokees, a majority of the SBEC's I've come across are flashable, only the really early ones are not. I'd be happy to lend you my flashable one if you wanted to use it as a guinea pig. They're also a dime a dozen at my local junkyard.
Click to expand...


Oh also I bought a mpscilink. Should be shipping to me sometime soon. Found all the memory locations for the Jeep SBEC to get mpscan to work. I assume Mpscilink will allow me to plug in memory locations so I can datalog with it as well...
 
Back
Top