Anybody interested in working with me to expand the resolution of the 8746 (7747) ecm's main spark table? How about eliminating the add on fuel table and just having one?
I believe it was RBob that that did make one fuel table for the 7747 but I don't recal much talk about it on this board. I might be on the diy-efi archives but I haven't seen it.
I really want to expand the tables because the spark only goes up to 3600rpm, anything after that is just what is "added" incremental vs engine speed. Example is the last line of spark vs rpm vs MAP is used for anything beyond 3600 but then there is an added constant which is incremental vs engine speed. This gets me in trouble and I'm not ALWAYS at a specific MAP at anything beyond 3600rpm....can we all say 3.73 gears and highway passing with stock valved tranny (anything past 1/2 throttle is a 4th to 3rd downshift). It's gotten to the point where I'm about to rip out the tranny and install a t56....then reality hits and I'm about broke.
I've got no EGR, no need for the AIR injection code and no need for a LOT of other crap that's in the eprom. I just need some help and am wondering if I should pull the rom off the ecm and go romless. I don't want to do this because I like my 8 in 1 flash prom adaptor but it isn't NEEDED.
Anyhelp would be greatly appreciated.

 

It is difficult (impossible?) to change the SA code, it is all in ROM. A good portion of the fueling code is in the EPROM which makes it easier to patch into.

To disable the onboard ROM just need to pull the ROMENB signal line low (ground it). Then place all of the EPROM & ROM contents into a single EPROM (128Kb). Another chip (74HC00) for address decode and you are ready to go. Even have an additional 4Kb of storage.

There are a couple of methods to eliminate the OD->3 downshift. The least expensive (which is good) and easiest (even better) is to plug the two holes in the TV valve. Ah, here is one of the better threads on this topic:

https://www.thirdgen.org/techbb2/sho...+AND+downshift

RBob.

 

Isn't the 3600 rpm limit good enough? I get what your saying about 4 -3 shift , but do you really cruise at 3600+ on the hiway? Me I don't cruise at more than 2700rpm, and at 3600+ rpm I'm at 80 -100 map (95% of the time). So the SA slope is good enough for me. But the idea to add to the table is a neat idea.

I would have thought with your mods you would have the "police B shift valve" by now.

 

There are a lot of issues with having the spark table ending at 3600, mostly because passing vehicles and then when I'm at the track there is only a couple seconds that my car ISN'T out of this range.
Right now I'm going to just work on this as a side project for the winter. With some help I'm sure I'll be able to do it, just a matter of time.
Anybody know how to deactivate the TCC decel unlock on a 7747 or 8746? I'll do a search but I just thought I'd ask since source codes is still on topic.

edit: That tranny mod is looking very good. Doesn't look like it'll take more than a day.

new-edit: https://www.thirdgen.org/techbb2/sho...ght=TCC+unlock found what needs to be done to disable TCC decel unlock, thanks.

 

On that tranny mod (pluging holes in the sleeve) just so you know tranny will shift out of 3rd at WOT at very low rpms (of course you can still shift manually), I did it on a buddys car, It works great other than that.

And passing somebody at above 3600rpm in OD, with 3.73s thats like 120 mph (too fast for me)

 

RBob, how did you expand the VE table into 1 large table?
If I wanted to expand the table from 3200 to 6400 I would need 8 more columns. Currently VE1 takes up $2B1 to $2F8, that's in an 8 by 9 table (72 locations). VE2 takes up $2F9 to $309 (17 locations). The table right above VE1 is EGR Injector Constant vs. Vac and that starts at $2A1 but it's only got 13 locations free.
If I were to expand the VE table by using the locations of VE2 and the EGR table that gives me 30 locations. The problem is that going from 3200 to 6400 (6375 to be specific) would require 8 columns if going in increments of 400rpm BUT that's with 9 rows for MAP!!! So I would need 72 locations but only have 30 , what are some options? I really want to keep the table together in one locations so TunerCat can graph it all at once.
Do you think if I just deleted unused tables and disabled them in the ROM then moved the surrounding tables/constants I could do it without getting a headache? I would obviously need to be ROMless with this method so that after relocating tables I could correct the links in the ROM code. I thought you were able to do this without going ROMless?!?!?! I'll take a look at the 7747 ecm later today to see if you've got it easy compared to this 8746.

edit: Okay, I guess the 7747 already has more room. The table above the VE1 in the 7747 is BPW Constant (egr) Vs. AIR FLOW Vs. %EGR and it's got 71 locations that could be freed up. I guess that makes me **** out of luck and more of a reason to go ROMless.

 

Yes, it is easier with the '747. They used a huge table for the EGR airflow information that is easy to eliminate. There is even additional code space that is freed up when that table goes away.

At this point I would recommend that you start to convert the '8746 hac into source that can be assembled. Then work on getting a test bench together along with a spare ECM or two (one for bench, one for car). Winter is coming and outdoor car stuff is no fun until spring again.

With this in place convert an ECM to ROMLess and start to meld the code into the form you want. Test on bench, go to car.

Currently I have two VE tables. A low speed (400- 2000 RPM) table with a row every 100 RPM. Map from 20 to 65 kpa by 5's then to 100 kpa by 10's.

The high speed table starts at 2000 rpm and goes to 6375 rpm. It is every 200 rpm until 3600 rpm, then by 400 rpm til 6375.

The other thing I did was to change the axis around. It is now map across (columns), by rpm down (rows). It now resembles the SA table axis and makes it easier for the brain.

RBob.

 

How hard do you think it would be to flow-chart the code? It doesn't look like it's all that much, just a whole lot of subroutines for converting input values.
I'm working with this new software called Labview for our Formula SAE team. It basically lets you input any kind of signal and you program how to read it and display that info. It's like programming drivers but there is no code. It's all one big graphical flow-chart. Very cool and expensive stuff but if I could flow-chart this source code I think it would be easier than using the Find function in word a million times. BTW, is anybody still working on programming a GM ecm to accept lamda from the wideband and self tune? I haven't seen any info about it on the diy-efi lists so I was just curious.
I will be getting the test bench up and running shortly. Infact I'm going to RadioShack in a few to pickup some parts for the Formula team, might as well get some parts like 555 timers and pots.

 

Flow charting the code would not be too difficult. It might be easier/faster to just document what is done is each routine. As the ECM is a real time system the code runs the same routines on a set time schedule.

Sorta like this:

Main dispatch loop runs 160 times a second. Does misc stuff like IAC stepping, MAP read, VSS read and ALDL bit banging, then dispatches to the proper minor & major loop.

2 minor loops that alternate. Each runs 80 times a sec. One for fuel the other for spark.

16 major loops that run round robin. Each runs 10 times a second.

The main dispatch loop is entered via an interrupt driven at 160 Hz. It will then dispatch to the proper minor loop. Once the minor loop completes the proper major loop is run. Once the major loop completes the code drops into a wait loop until the next 160 Hz interrupt. The sequence above repeats running the other minor loop then the next major loop in turn.

Stuff like the diags, reading the CTS and IAT, controlling the shift light and TCC are done in the major loops. Time critical stuff like timing and fueling control are done in the minor loops.

The is also an init routine that runs at ignition on along with a factory diagnostic routine that nevers runs (unless you use the secret code).

I've seen some auto-learn stuff based on the DIY-WB in operation. One was a Turbo Gran Prix (3.1l v6). I futz'd around with it and had some stuff operational then decided not to do it. Easier and safer(!) to just pull the WB data from the log file and post process. Even reads the source code for the VE tables and creates new ones to paste back in.

RBob.

P.S. The above ECM info is true for the '747 & '8746, YMMV.