Hi,
While over the last couple of years I have only ever fiddled with the auto transmission tuning of my ECU, I've recently put a twin-throttle manifold on my engine, requiring a little tuning of the fuel tables. I've only ever changed idle fuel, and just have, what I hope, are a few simple questions.
For starters, I'm from australia and am talking about tuning a VR Commodore ECU. The ECU I'm working with is a 16176424 with $11 code. The definition file I'm using is the 'version 3' of this ECU that is on most FTP/download sites.
What I am wanting to know is what tables affect open loop fuelling, and which ones closed loop fuelling?
One of the flags that are set specify that the code will use the AFR table, rather than the simple stoich value, so I'm assuming the AFR table (F60) is the closed-loop fuelling table? But how do I change the open loop fuelling? Is it controlled purely by the VE tables, or is it the Cold Engine AFR (F56) table?
Another question is with this definition file, what does the "AE Gain vs Delta Manifold fuel" table do? I know what the other AE ones are for, but not this one.
And one last thing that has me confused is PE. The cam I have in the car means it idles at 50kpa. Under around 40% throttle its reading 100kpa. Now how do you alter the PE for say between 40% throttle where its reading 100kpa, and 100% throttle where it is also reading 100kpa? Wouldn't the computer see the same load? Is there a table reference that is missing from this definition that somehow brings TPS into the PE equation.
Sorry for all the questions, but I've been fiddling with the fuelling side only for the last couple of weeks and just need a heads up in a few areas.
Thanks,
Simon

 

No one have any ideas? If I've posted this in the wrong area, or on the wrong board, does anyone know where I should be posting it?

Thanks,

 

VE is the "main" table to get the fueling to match what the 'commanded' AFR is. For instance, if the ECU is commanding 14.7, tune the VE until it gets to 14.7 everywhere, then go open loop if you like.

AE Gain is acceleration enrichment increase, due to changing MAP, almost always in coincedence with a throttle change as well.

PE is typically enabled at a %TPS value. Yes, the engine can be at 100kPa and 35% throttle, and also at 100kPa at 60% throttle. One would be at a leaner AFR, the other at the PE AFR +PE spark as well. Yes, they are *almost* the same load. You might be able to see 1-4% difference between 40% throttle AFR and 100% throttle, especially at altitude, but don't sweat it.

The AFR table is just a commanded AFR table. You'll want to use a wideband to match actual AFR with commanded AFR, using the VE table. Another legitimate way would be to run closed loop with a narrowband, get all VE adjusted to get 128 BLMs and INT, and then switch to run the open loop AFR table. It should be close enough.

The cold engine open loop AFR table is just to get the engine to run smoothly, by richening it a little, and to compensate for the fuel that gets wasted with a cold engine, and to compensate some for the denser charge. Fine tune this table AFTER the VE is squared away. VE is king in speed density - it is what the ECU "thinks" the engine is flowing for air.

 

Thanks for the reply. Just a quick couple more q's:
With regards to the AE gain, what does the 'manifold fuel' refer to? ie. the table is labelled "AE Gain vs Delta Manifold Fuel", but how does the change in "Manifold Fuel" relate to MAP?

And lastly, do all GM ECM's use PE functionality? Or is it possible that they rely on the AFR tables for the enrichment? I only ask as the definition file I have is quite comprehensive, however it doesn't contain any PE details at all, nor does the TunerCAT TDF file, which seems strange to me that both would emit this data...
Thanks again

 

Delta Manifold Pressure fuel is what it probably should say. dMAP fuel in other words. Fuel is just tacked on at the end because it's AE Fuel, with gain vs delta stuck in the middle.

All the GM stuff I've seen has PE fuel. Is there anything labled "WOT fuel" "CAT or COT (cat over temp) fuel" or "High or Full throttle/load" fuel?? The PE table could easily be shown as a AFR table, but it's usually it's own table (and not part of the usual Open Loop AFR table), and is usually entered via conditions such as TPS thresholds.

 

Ahhh, that makes more sense...

Nope. Just had yet another look through all the tables in the definition, and nothing that would suggest PE, or anything that you've suggested.

I've attached the xdf file if thats of any help. But as I said, I really can't see anything that stands out as being used for PE

 

Use the target AFR table (F60) for PE and AE params for throttle pump stuff. Have a look at the F60 table and u can see the target is around 13:1 or so in the 90-100kPa region. If target AFR < stoich then a PE flag is set, it is not used for any engine functions though just for trans pressure modifiers.

The $11 xdf is largely complete for the engine side of things but very much incomplete for the trans.

Manifold fuel as far as i can work out is actually a modifier to the AE or DE multiplier based on how much fuel is in the manifold at any given time. It is something that i was hoping somone smarter than me could work out in the hack, i have commented it just dont fully understand the math behind what its doin

 

Awesome! Things are slowly starting to make sense... So basically the targer AFR table is used for both closed loop and open loop fuelling when at operating temp ??

UNEEK, do you have a copy of the hack you would be able to share? I thought I'd looked for it and came up empty handed, but one may be lying around

Thanks for all the help so far guys

 

Yeah its used for both, if the target is == to the stoich value (KAFSTCN) then its closed loop otherwise it will be open loop. There is an option flag to use just the stoich value or the F60 table to determine closed loop.

I didnt know of any so decided to start one earlier in the year. I am still working on it and will be released later when it is more complete and more importantly correct. There are more trans tables than you would ever know what to do with.