Does anybody know how lean you can run your tables at idle and cruise?
I have a 95 LN2, and have identified the stoich constant, which at normal cruise the vehicle uses this constant to maintain the fuel mix.
I was thinking something along the lines of 15.5 or 15.7 for gas mileage with retarded timing to prevent detonation, but im not sure as my tuning experience with this engine so far has been for power output.
retarding timing will not help you get better gas mileage, you would have better luck with gearbox adjustments, lighten things as much as possible but going up above 15 in AFR isnt good for the motor also your car will never run consistant AFR while cruising it bounces up and down
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Its lightened up as much as possible. I've also loaded up 17"'s running 45 series tires, so the gear ratio should be ok. I've gotten some better gas milage with advance timing, but im thinking if set back to stock time and lighten the cruise AFR it should run a little better as far as mileage goes as long as i dont get any knock.
Of course, i would say im a year 3 student at this so im not the most enlightned tuner, though my ride does tout speed, as it will be even faster soon.
hmm too bad hp tuners cant unlock that for us
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Lean cruise mode was originally called highway spark and highway fuel modes. Once upon a time these modes were enabled. Due to the way the EPA tests cars for emissions, the highway cruise modes would never be active during the testing. Yet they did help during mileage testing and they could increase mileage considerably if implemented correctly. When the EPA realized the standard test procedure completely failed to test lean cruise, they labelled it "emissions defeating" and made it a big "No-no!" This was in the late 80's or early 90's. If it's still in the OBDII code, I'd have to give GM a big thumbs up for continuing to make it available.
Chris, you'll have trouble using the stoichiometric AFR value alone to adjust the lean cruise. Stoich is a constant which many other variables depend on. What works best is watching the MAP and going for leaner mixtures when MAP values are low. Highway mode fuel generally added a timer, a VSS option, and a monitor for engine temp. The engine had to be warm, the vehicle had to be moving, and MAP had to be below 30 or 35 kPa for a certain time limit, often 50 seconds but sometimes more. Whether you try to add these qualifiers or not, you'll need to do the same as GM with their highway fuel and force open loop operation to obtain leaner than stoich ratios. Once in open loop, you can alter the VE tables or, possibly, a desired AFR vs MAP or throttle angle table to get the lean values you want. Experiment... I've had lean operation as lean as 16:1 in some vehicles. In others it's just not possible to get far from stoich. I'd expect the 2200 to run well at 15.5 and light load.
Ok thanks for the info,
I will be doing this on the 0D mask, as i needed a solution to my odb1 ecu stuff right now, this doesnt mean the odb1 project is dead rather im working the 6285 benchside to map it out fully.
I have seen how this highway mode code works, and should be able to implement it no problem, i was looking also at a roadway mode which effectively would allow for leaner than usual cruising mix in town, could this be done via map values????
You can probably rig something up in code to do what you want. Least desirable but easiest imo is to run in open loop and lean out the VE tables while increasing the spark advance during cruise conditions. You might even be able to play with the closed loop enable parameters to force open loop below a certain TPS when the vehicle is moving. Next easiest way might be to enable PE at all times, then adjust spark and fuel to go from lean to rich depending on RPM and TPS. It's worth a try and would help you understand some of the code. A more difficult way might be to modify the code which looks up desired AFR vs coolant temp. Once the desired AFR is obtained, check for coolant temp > 80deg C, vehicle moving, and that TPS hasn't changed for 40 seconds. If these conditions are met you can lookup adders in a table you create and modify the desired AFR accordingly. So if tps is 0% you could add .7 to the desired AFR, if tps is 10% add .5, if tps is 20% add .2, and for all values of TPS 30% and above, add 0.
Hrmm food for thought.
I think it may work but i dont yet have enough of the 6285 code decyphered.
I will work it more, if anyone out there has worked the code let me know. If you want to work the code, odb1 ecu thread will have the most updated source posted. If anyone has any new additions to the source, email them to me firstname.lastname@example.org and I will get them into the updated source.
6285 is going open source, due to my inability to work it. Meaning a final tuning solution may be free, or at least only cost hardware.