Jeep SBEC PCM tuning (91-95)

sev80 said:
That part is very easy. There's wiring diagrams online. The hard part is the coding experience (which I somewhat lack). Would love to have another hand on the project! We're very close to getting the stock ECU to flash. Late 94 and 95's are flashable. Like A_kelley mentions, if the case has screws, it is not flashable, if it has snaps, it is.
Click to expand...

I went to two pick-n-pull yards. Including the ones I have, I now have 5 ECUs:

1. (pictured left.) Mopar R6026790 "remanufactured" PCM for 1995. (It has torx screws.)
2. (pictured right.) 56028113 Federal or High Altitude (w/o Export Pkg.) Stamped# 56028112 for 1994 (this looks like 56028011 on the inside)
3. Original 56028011 for my V8 1993 (not installed)
4. 56028026 for a 1995 4.0 (got this just for kicks)
5. mopar performance ECU P5249518 (installed in vehicle)

Which are useful for boosting my V8?
Which are not compatible 95 vs 93?
Which can I dump the flash memory from?
Is the 95 4.0 ECU useful for reflashing as a V8 or is the board physically different?


20180206_162216.jpg


pcm-scr.png
 
Whoa! that is super interesting, the one on the left looks like no other Jeep SBEC-II ive ever seen. It actually looks like a passenger car/turbo mopar SBEC-II. I wonder if truck and car SBEC-II's are are interchangable with the only functional difference being the cal itself?? That cant be... Weird!

Im not sure if that reman one is flashable. You might have to taking a bit of the potting off and take a peek. The one on the right is not flashable. It would need to be socketed to work its the older one. Basicall you need a mid 94 and up ECU to be flashable. You CAN make the one on the right work, you'd have to take off the potting material, unsolder the eprom, solder in a socket and get a 27SF512 chip and a burner.

I'd be very interested in your high altitude cal and also the mopar performance one. Mind you, Andrew and I are working on 4.0 Cals. V8 wouldnt be too different. The thing we're not sure is the hardware difference between the 4.0 and 5.2 SBEC's. Mainly, if the 4.0 ones have extra drivers to drive the extra injectors. We do readily have the capability of dumping out the rom's from these units without unsoldering/touching anything.

93-95 are all interchangeable, provided its the same engine. I think the pinout between 6 and 8 is a bit different. The flashable SBEC-II's fit in the same size case but are physically smaller and have thinner heat sinks than the older non flashable ones.

We're a bit far off from FI cals. I'll let Andrew speak to that part.


Say, how did you find out about us? Was it from the jeepforum post I made? Wondering if my outreach worked ;)


Edit:

Here is what the flashable boards look like. Note the position and size of the board vs case and the position and thin size of the heat sinks. Totally different layout

IMG_3546

IMG_3546

 
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Right now, It takes a few steps to get set up to dump the roms. You need a 5v FTDI cable, a circuit to bootstrap the ECU.

This means applying 12v+ on the RX line of the SCI bus as you power on the ignition, then taking away the 12v. You have to protect the TX line on the FTDI cable during this process or else it will fry. Then you have to run a program that will dump the rom out. AKelley and I have this set up on the bench so we can readily do it. The eventual idea is to offer a device that will do all this plus flash with minimal setup. What would be helpful is a dump of your 93 cal and then the mopar performance cal. AKelly should be able to identify the tables and see what the mopar guys changed on the fuel and spark side. Could be interesting to see what the JTE guys tweaked back in the day.


Is your reman SBEC was from a 4.0 or 5.2?
 
reman was a 5.2. they are all 5.2 except for the 4. on the list

i have never heard these terms before: FTDI, SCI, JTE, SBEC.

i don't know what "protecting the TX line" means -- which is the TX line on the 60-way connector?

i don't have a "12V source" -- do you mean a bench power supply? -- what do i need to buy? i do have a 110V to 12VDC cable from a dead laptop.

i assume "powering up" means connecting some of the 60-way pins to something. I have no idea what to connect to what.

i can use my sodering iron quite well -- it has a temperature control

I think you need to write up an idiot-proof tutorial with a parts list and exact diagrams of what gets wired to what.

my embedded work was always done in tandem with an electrical engineer who got everything hooked up to my PC. i only had to push a button to flash my work to the board --- and i never had any idea what that button did TBH.


sorry to be blunt -- but i think it will save us some time if you know up front exactly what i am clueless at

i have done linux kernel developed, ethernet driver development, interrupt code in assembly, and so on. so it should be simple for me to reverse engineer this code.




pcm-head.png
 
There is also another route to mod the eprom ecus that allows in circuit update also, using a more common chip. I'll post more later on that. V8 can only be the on boards that have 8 injector drivers. If you use a ecu from a V8 zj or truck you'd be good to go. Boost depends on the code.
 
If you've got an email address, pm it to me and I'll send you a Jeep bin, the disassembler, and a disassembled tm bin for boost and you can see if you can merge them together while Sev and I figure out the hardware.
 
I've actually got an ecu like the one on the left. It should have a 87c257, which requires a latch board. The one on the right with the grey connector rubber seal is possibly flashable. (That was another differentiation I noticed). There is a way to rewire a sbec that uses a 28 series eeprom in place of a 27 series eprom. That is described at the beginning of this thread to some degree.
 
sorry if i am shooting blind with this question:

the EEPROM chip in the board picture is this one, right? ---

https://www.mouser.com/ds/2/268/doc0006-1108095.pdf

surely the easiest is to just unplug the chip, then plug it into this:

https://www.amazon.com/Signstek-TL866CS-Universal-MiniPro-Programmer/dp/B00K73TSLM/

or this:

SPI 25xx PCB5.0T-2013 Willem EPROM Programmer BIOS009 PIC Support 0.98d12 Adapte | eBay [ I just bought this -- :-( trigger happy i guess ]

then swap it back when you are done?
 
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SBEC Code.zip
@GarageBuild there's the link for the file I was trying to send. Gmail being stupid on my phone I guess.

As far as that link, yes you can do that. However that's a thirty minute process and is not flashing. That is reprogramming a eprom. That requires modifications to the ecu (replacing chip as well as adding circuitry) to "flash" in circuit, in vehicle. Same end result, different approach, more labor intensive and time consuming. You don't want a 30 minute cycle Everytime you change the code/tables. Flashing in circuit takes 1 minute, and only requires it to be plugged up, no uv light, no swapping chips. That's so 1980s-early 90s. You'll see what I mean when we finish up the flash stuff.
 
a_kelley said:
SBEC Code.zip
@GarageBuild there's the link for the file I was trying to send. Gmail being stupid on my phone I guess.

As far as that link, yes you can do that. However that's a thirty minute process and is not flashing. That is reprogramming a eprom. That requires modifications to the ecu (replacing chip as well as adding circuitry) to "flash" in circuit, in vehicle. Same end result, different approach, more labor intensive and time consuming. You don't want a 30 minute cycle Everytime you change the code/tables. Flashing in circuit takes 1 minute, and only requires it to be plugged up, no uv light, no swapping chips. That's so 1980s-early 90s. You'll see what I mean when we finish up the flash stuff.
Click to expand...


thanks

that all makes sense


BTW for interest, both the stock and mopar ECUs behave as follows:

right after install the jeep can barely keep idle and it drives awfully.
then after an hour of driving it's smooth --- and it passes emissions.
so I am inferring the ECU is "learning well" but from a Bad initial set of tables.

(i have bosch injectors that deliver about twice the fuel -- estimating from the overhead computer which shows double the mileage)
 
The ecu does not relearn the fuel tables. It does however learn corrections for idle and part throttle. WOT goes open loop, with no feedback or learning of values. The tables that are programmed are the tables that are used in all calculations, and the learned correction is applied as long as it is within the parameters to permit it to affect fueling. As far as I know, even modern ecus function in this manner, excepting that they tend to stay closed loop under broader conditions.

As far as what injectors you have, I would check the flow rate compared to stock injectors. That's the true way to determine how much fuel needs to be adjusted to compensate for the oversize.

There's 3 ways to accomplish FI in the ecu..
1 - dual tables: switch for vacuum/boost
2 - rescale existing tables for -14 to +14
3 - merge existing fi code with the Jeep code

Each has its own appeal and troubles. Any route is not trivial, simple or straightforward. I can do either of the first two, but getting the flash units programmable is a higher priority for me at this time.
 
If the injectors flow rate is double that of a stock injector, yes (assuming the injector latency is the same). The fuel trim cells only allow for about +- 25% trim in closed loop.

Look up the flow data on stock injectors and the ones you put in and post up the flow #s. Also the overhead trip computer relies on data from the ecu to calculate the mileage. It doesn't know about the bigger injectors except when in closed loop with fuel trim applied. It's based off the flow rate of the stock injectors and will be out of calibration.
 
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I looked up my injectors....

They are 249CC (Bosch 0280155715) vs stock which is 205CC. My stroke is 3.58 vs 3.31.

So roughly (249 / 205) / (3.58 / 3.31) = 1.12 => 12% overfueling. This is within the 25% you say.

So obviously the overhead computer is giving completely bogus numbers.
 
GarageBuild said:
I looked up my injectors....

They are 249CC (Bosch 0280155715) vs stock which is 205CC. My stroke is 3.58 vs 3.31.

So roughly (249 / 205) / (3.58 / 3.31) = 1.12 => 12% overfueling. This is within the 25% you say.

So obviously the overhead computer is giving completely bogus numbers.
Click to expand...

So what's your displacement percentage difference? Are the injectors latency close to each other? If they are not, that needs to be adjusted first before trying to do anything else.

Really you need to datalog to be able to correct the fuel tables. Like I said before, once the flash units are taken care of, we will move onto tuning the NA cals since then they will be useable. The older non flash ecus have to be modified and a eeprom/flash chip and possibly a latch board depending on which chip is used. (87c257s require a latch board, 27c256 does not (but does require some pcb changes) I might have the wrong pn there on the 2nd). Once it can be flashed, it can be tuned. It can be done with a narrowband for NA but widebands make for a better & easier tune. There is also code mods that need to be done to allow a wideband analog output to be connected directly to the ecu to allow datalog to capture everything (RPM, map, wbo2 is what I would log to tune one). The datalog software also needs developed but will use the same interface as flashing so it's a 2-in-1 tool. This is really a multi stage development. Plus we will possibly create an additional tool that reads the data log and will tune for you based on a desired afr table. all of it will get documented into a page to form instructions to go along with the tools & hardware. This all will happen before I get into converting a NA cal to FI.
 
Interestingly enough, there is some cross over from the Magnum SBEC2 cals to the Jeep cals, but from what I've seen they are considerably different. For example, the Jeep cals have a 2d table type that is unique to the Jeeps only, not found in either the Truck cals or passenger car cals. Looking at the earlier Renix calibrations, I have a hunch that those table types were ported over from Renix to the Jeep SBEC2. This would make sense since I've seen comments that indicate that the calibration work for both ecu types were done at JTE at PROC. Additionally, the VE table appears almost the same between the Renix and the SBEC2, even the characteristic of being maxed out in the low manifold pressure areas of the map (high vacuum). Jeep SBEC2's use single value power enrichment FA modifiers with rpm and time based qualifiers, which is considerably different that the Magnum calibrations that use a part throttle enrichment table (3d) and a full throttle enrichment table (2d). In other words the Jeep 4.0 calibrations seem a bit simpler compared to the Magnum cals. Since the Renix worked fairly well, I suspect that they just ported over what they could since there is no reason to re-invent the wheel, whereas the Magnum MPI engine was new, and whoever was responsible for the calibrations wanted some additional functionality in the cal. The VE and timing table size and function are the same between Jeep and truck, and that even carries over into JTEC all the way through the 2006 model year. The difference being that SBEC2 fuel map is a fueling correction map with a fuel offset and map multiplier factor, where as the JTEC is a straight pulse width lookup fuel table in 16 bit resolution. What you will find is that with cammed engines that don't make much vacuum, you will not be able to pull enough fuel out of the fuel table. This also reflects in the fueling being maxed out in the high vacuum areas of the map. You can increase the fuel scaling factor and change the pulsewidth offset, but it's somewhat of a compromise
 
Welcome to the madness, Chris. :) Great insight as always!
 
I put my Jeep on a floor dyno here in Dallas. I get 200 HP, but at WOT it is running at 11:1 air-fuel - *very* rich. PCM also seems to limit to 5500rpm -- whereas performance engines rev to 7,000. I also have stock intake manifold, TB, and hat.

So considering these limitations the performance isn't bad. (The Dyno guy was impressed -- says I get about the same performance as the Dodge 5.9s that come through here.)

The rich fuel is consistent with Andrew's WOT note above and my injector estimate.

I also got hold of a "no screws" 1995 PCM for the V8.
 
Here is a video of a 360 getting over 400 HP -- my 200 hp now seems really embarrassing considering I have hughes iron heads with bigger valves and intake ports.

I am thinking that if I install a performance intake (i have one on the shelf) and put in a cam with better timing, then I should get 300 hp at least.

So basically this means I can forget about turbo-ing the thing and just tune it.

(See numbers at 10:21 -- BTW wheel is 82% of crank according to the interwebs.)

 
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@GarageBuild

I wouldn't necessarily say forget the turbo, but definitely opening up the intake tract, cam and getting fueling & timing right will get you improved power. Turbo will still get you more power than NA but everything comes at a cost. You can get 300-350 out of a Jeep 4.0 i6, all motor... But if it's designed for all motor, it likely won't take boost well.
 
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