89vette

$8D Code

I'm helping a friend that is having an issue with this PW maxing out at 8.1 at 3800RPM. He is running 38 pound injectors in a 434 Super Ram car. He keeps adding fuel but nothing will make the injecotrs stay open past 8.1 from 3800 to 6375. Could it be false reporting in Diacom? I looked at all the tables (using Tunercat) and I didn't see any table that would limit the PW.

Thanks

JP86SS

iTrader: (1)

Could be the PW limit discovered (and corrected) by Z69'.
https://www.thirdgen.org/techbb2/sho...hreadid=276420
The link is from the tuning guide in the stickys.

89vette

I read that when I did a search and I think I need to drink a beer and read it again. It's been a few years since I have messed with this stuff.

junkcltr

iTrader: (1)

The end result is swap the two lines of code as JP86SS said in the linked thread. You could also run the SAUJP code which already has the swap/fix.

The swap/fix works. I have a 13-14ms injector PW at 3200-3600 RPM on a stock 305ci TPI engine with 30#/hr injectors.

Grim Reaper

89vette, Z69's post explains the fix but didn't explain the initial problem. The initial problem with $8D, is there is an internal rounding error caused by a combination of very large injectors and/or very large displacement.

Prior to Z69's "fix", the "workaround" was "fib" to the ECM and pretend you were using a smaller combination of displacement and injector size in the appropriate "ratio". However, this did cause other "tuning issues" where only one of the parameters was used in the calculation but the other was not. Z69's fix resolved that issue.

The S_AUJP is the best way to go as it also fixes and improves a number of other issues: 1) such as the highest desired idle speed being limited to 800 rpm when the transmission not in Park/Neutral and 2) increasing rpm limit to 6400 rpm fro 5600 rpm on the Extended VE Tables.

89vette

He is running a 90 Vette SD bin for a manual. Where is the location that I have to change the code in that bin?

Grim Reaper

Eek...The code of the Vette SD bin is different than the F-body (AUJP) bin. A lot of the code is similar but there is some specific differences within the code itself and much of the code itslef doesn't match up to the F-body's AUJP.

I am not sure if the AUJP bin will run properly on the Vette's 727 ECM - my raw gut feeling is it will "mostly". The AUJP doesn't have an Oil Temp Sensor like the Vette's. But it is woth a try. If the AUJP runs properly, then you go with the S_AUJP. But if the AUJP doesn't, then the S_AUJP won't.

89vette

We are both running the 730 ECM and not the 727 ECM since they are both 89's that were originally MAF cars.

89vette

Is the fix to fib the ECM to decrease the cylinder volume constant say by 20% and also add 20% to the injector constant?

JP86SS

iTrader: (1)

Actually it does. Its just not connected in the F bodies but it is all there.
The code isn't terribly different from what I've seen, just little bits here and there.
If you do the search for the pattern in a hex editor it should be easy to do the line swap. Have one more beer and take a look.
It would be worth the try.
What bin are you using?

89vette

I'm using AXCN bin. I use the hex editor in GM Epro to change the code if I can't do it in Tunercat. I don't have the ability to find a pattern. What pattern would I look for? I saw the values for the new code but did not see what the stock values are so I can look for them. Thanks for you help.

89vette

AHHH! Now I understand. I found the code in the AXCN bin. It is located at 4C79 - 4C80. I also understand what to swap. I'll try it! Thanks

Grim Reaper

In that case, I would use the S_AUJP because of all the other fixes within the code. Why re-invent the wheel?

89vette

This may be a stupid question but does the injector constant in the code use the injector constant (1/injector constant)? I guess a better way to ask is if I am using 30 as my injector size in tunercat, do I still use the following code:
FE 84 1C BD E4 2C DE F1

JP86SS

iTrader: (1)

This bin is using the $24 like ANHT.
You should change it to be :
FE 84 1C BD E4 24 DE F1

This is an addressing issue and does not relate to injector sizing (or TC for that matter) Just the way the ECM looks at addresses.

89vette

But the code in the AXCN bin has a 2C and not a 24. If you read the post explaining this, it clearly says not to change BD E4 24 and to just swap either side. Am I missing something?

JP86SS

iTrader: (1)

You are correct in that but I opened up an AXCN and saw 24 ????
Maybe my bin is FUBAR.
If its 2C then it should remain 2C, if 24 then 24.
Jp

Just looked at 3-4 other copies with diff names and they all show 24.
Sure you have AXCN ??
Doesn't matter, just do like above 2C = 2C etc.

junkcltr

iTrader: (1)

24 is a BCC, branch if carry clear (branch if greater than or equal to zero)
2C is a BGE, branch if greater than or equal to zero

They are the same thing. Use the value you have in the bin.

It sure looks like GM used a compiler for the code and it changed how it interpreted the high level code.

RBob

iTrader: (1)

A BCC is unsigned where a BGE is signed, so they are different. In this case it doesn't matter as the 24/2C is the LSB of an address for a JSR.

89vette, as JP posted use whatever is in your code. Although I too wonder why it is 2C, maybe GM did a code tweak to AXCN along the way. Usually they change the broadcast code (BCC), but one never can tell.

RBob.

89vette

I looked again at my bin and my buddies bin and there IS a 24 there and not a 2C. I'm now sure how I got those wires crossed. Sorry for all the confusion guys.