In TP ver4 I downloaded the contents of my stock tune a 91 Corvette and did a ton of reading here and found some things but not others. I am hopeing the $8D.xdf is correct though it has me wondering at times. Here are some of the issues I don't really understand.

Main spark table shows numbers as high as 47 degrees at part throttle yet only 23 at WOT which seems very light and then has a constant of max timing of around 41 why put 47 in a table if it gets clipped to 41?

Highway mode all constants seem to make sense yet min speed set to 255 mph??? So no highway mode at all why throw this away?


Some thoughts I am trying to get familiar with all the tables tuning hardware and software well before I make engine mods so I am not wondering if it is the mods or my lack of understanding the tuning program and tuning hardware.

I am used to around 7 to 10 more degrees of timing at WOT. Granted the cam is very short duration stock but saying that the VE tables fall like a rock after 3600 rpm so there can not be much cylider pressure going on either. Any thoughts sure would help.
Dave

 

Head up to the Tuning Guide Book sticky. See chapter 5, '8746/'8063/'7747 ECMs, SA Logic thread.

Highway mode all constants seem to make sense yet min speed set to 255 mph??? So no highway mode at all why throw this away?

EPA. NOX goes up in lean cruise.

I am used to around 7 to 10 more degrees of timing at WOT.

PE mode SA. Discussed in the SA Logic thread.

RBob.

 

Ok looked at those but the spark vs. PE seems redundant in a lot of ways. It links timimg to cam and throttle body size rather than actual load that the 3D spark table does. With a larger throttle body that i currently do not have I would get closer to full load 100 kpa at a smaller throttle setting due to the larger butterflies yet not get into PE mode TPS position. My 91 is SD so it knows nothing about actual airflow only inferred from manifold pressure. I come from over 20 years of aftermarket EFI and for spark we have 3 main table spark vs. load and correction tables for engine temp and air temp. Idle spark is something else again but goes away after you leave idle and only used to trim the idle speed 50 to 100 rpm. I will play with highway mode after everything else works just fine and can always turn it off if it makes too much NOX. My daily driver has it as I get about 3 more mpg on 92 octane than 89 and smart enough to know octane more than required helps nothing if the tuneup is not changed. In the mapping for my 91 vette the highway mode does not add any timing but does change the target AF ratio from 14.7 to 15.50 and looking at the timing tables at light load they are plenty aggressive already.
Dave

 

PE mode is a means of dropping out of closed loop into open loop for more power. In PE mode there is spark timing added along with a lower commanded AFR.

In this regard it makes sense.

As for the different size TB's. Change the TPS% vs RPM table to enable PE mode.

Note that $8D also has octane routines to adjust the spark timing.

Maybe some day the aftermarket will catch up to what GM produced 20 years ago.

RBob.

 

In all due repect the aftermarket has far surpassed what GM and others are doing now and certainly did in 91 but will let that dog lie.. I was initially asking about table organization and i am sure GM had their reasons for doing it that way rather than getting into a peeing contest as to who makes the best system. If your goal is to lecture me in my capibility please do not reply until you have set 13 world speed records the last in a under 3 liter motorcycle streamliner that went 376 in a measured mile and 394 mph out the back door. I have probably won more NASCAR and SCCA races than you have watched on TV... So please do take a breath as I will too. When your stuff is running 32 bit code at over 33 MHz and 16 meg of data logging at 1000 Hz and user definable 4 D tables let me know who is lagging.. I thought I asked an honest question about a ECM I was not familair with rather than be treated like this.. If there is a moderator please take note... Dave

 

LOL.

RBob.

 

WOW.... this thread.... WOW.

well, dave, RBob is definitely the person you should be talking to, since not only is he a moderator, he's VERY fluent with how the GM ECMs work.

 

My problem is simple the logic makes no sense and want to make sure what I am reading is right or I have a hosed up XDF file. I question why you would bother tying PE to throttle position in the first place as load is a map based function. There are a bunch of ways to get to 50% throttle depending on gear and load but only one way to get to map. I also found negative fuel enrichment for PE and not a believer the engine gains 13% VE in 400 rpm but only after 60% TPS and the losses it either side in 800 rpm and then not change the rest of the way to redline. After spending 35 years on a dyno with everything from street engines to full race stuff that easily makes 350 hp per liter this mapping just looks way off the mark as far as the smell factor goes. Compared to what I am used to working on the ECU in my 91 Corvette is an anvil or thereis a ton of things not documented..
Dave

 

https://www.moates.net/files/5)%20So...20Hacks/8D.zip

not sure if you can get to that or not, but that goes and defines every byte in the calibration and a lot of the algorithm for the $8D mask.

depending on what XDF you're using, you MAY have one that wasn't very filled out, there are multiple 8D XDFs running around.

 

I can and have a copy and now I guess print out all 300 pages and give it a read comparing to the XDF file. I am fluent in assember for Seimens stuff and I am sure it is more of the same just a different dialect. Sometimes I wonder if it would just be easier to swap out the ecu entirely and if was not for the fact cthe ECU is linked to the BCM and everything else I would gladly head down that road though I don't see a 91 Corvette no matter how nice worth the effort.
Dave