Is lean cruise possible for an LS2 GTO?
Thread Starter
TECH Resident
Joined: Apr 2009
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From: Wouldnt believe me if i told you
Is lean cruise possible for an LS2 GTO? I looked around a lot and i know the PCM is different then the ls1 gto, but is there anyway to "create" or program in a lean cruise in 6th gear?
To me it seems like on the highway when cruising i spend most of my time in 6th and dont really do much "performance" driving in 6th gear.
I havent been able to find anything about something like this, but i think it wold be a really great feature as ive already flirted with 30 mpg in dead stock form many times.
To me it seems like on the highway when cruising i spend most of my time in 6th and dont really do much "performance" driving in 6th gear.
I havent been able to find anything about something like this, but i think it wold be a really great feature as ive already flirted with 30 mpg in dead stock form many times.
On The Tree
Joined: Sep 2007
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I have been doing 16.0-16.4:1 cruise for years now in my all iron 231 v6. I use open loop and adjust the open loop afr modifier's to give me this lean cruise.
I find it works better with E85, but all fuel's show major MPG gains, the only tradeoff being more NOX emissions. You may have to pull back timing if you previously added it, but a stock timing curve and high octane gas combined with lean cruise usually works beautifully.
I wouldnt try it in a SD car that I plan on daily driving, but assuming you are running maf, go for it!
I find it works better with E85, but all fuel's show major MPG gains, the only tradeoff being more NOX emissions. You may have to pull back timing if you previously added it, but a stock timing curve and high octane gas combined with lean cruise usually works beautifully.
I wouldnt try it in a SD car that I plan on daily driving, but assuming you are running maf, go for it!
Thread Starter
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From: Wouldnt believe me if i told you
Is it possible to change the factory pcm logic?
For example if i go get a tune is it possible to tune my 6th gear lower RPMs for lean cruise? Possibly all of 6th even as i dont race thru 6th haha
TECH Enthusiast
Joined: Feb 2008
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From: Ventura, Ca
Lean cruise has the tables built into the code but your tuner software may not be showing them. It is a matter of getting to the tables and setting them up. I looked into it for a 04 GTO 243PCM setup. I am just not there yet. If you go to some of the Aussie forums they can give you the tables and what they are showing. Monodax is a place to start since there are some posts about this and what the tables are and the values. Note that the cars down under have this enabled from the factory. Don't believe anybody if they tell you otherwise. They even have some tunes for the 411PCMs.
11 Second Club
Joined: Oct 2006
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Just populating the tables wont get lean cruise going in a U.S. platform vehicle. The ls1 pcm was easy to get around with a .cax file that changed the code. I dont know if anyone has done this for the later OS's though.
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There are two elements to lean cruise. One is the actual
leanness, the other is the logic about when and when not
to go there, how to ramp in and out, etc.
The leanness, you have an alternative. The logic, you don't.
To cruise leaner, first determine the airflow ranges and
airflow_mode index ranges that correspond to "cruise".
Then go to the O2 switchpoint tables and bump the
cruise-region voltages down to (say) 300mV. This will
drive closed loop mixture toward the lean end. Scan it
and see where you've gotten to, and adjust from there.
I wouldn't go below 200mV, just to be sure the sensor
has room to overtravel (you need threshold crossings
to work). Stay maybe 100mV above the bottoming-
voltage worst case.
leanness, the other is the logic about when and when not
to go there, how to ramp in and out, etc.
The leanness, you have an alternative. The logic, you don't.
To cruise leaner, first determine the airflow ranges and
airflow_mode index ranges that correspond to "cruise".
Then go to the O2 switchpoint tables and bump the
cruise-region voltages down to (say) 300mV. This will
drive closed loop mixture toward the lean end. Scan it
and see where you've gotten to, and adjust from there.
I wouldn't go below 200mV, just to be sure the sensor
has room to overtravel (you need threshold crossings
to work). Stay maybe 100mV above the bottoming-
voltage worst case.
Thread Starter
TECH Resident
Joined: Apr 2009
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From: Wouldnt believe me if i told you
Wow. Thanks for all of the advice and info. Really great answers from everyone. I will Deifinitaly relay all this to my tuner next time i have a chance, and will try to make this happen when i get a re tune for any future mod.
Thanks again.
Thanks again.
On The Tree
Joined: Sep 2007
Posts: 198
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Depending on what OS you are using, there should be a "open loop airmass vs rpm vs commanded afr" table. This table will let you command different afr's at whatever airmass you want. Obviously just put it in around the cruise cells.
Last edited by darkhorizon; Jun 18, 2010 at 01:23 PM.
Lean cruise should not only lean it out, but also ADVANCE the ignition timing, not retard it. Your EGT's go DOWN as the ignition timing is advanced. It crosses over, meaning it goes lean and ADVANCES timing when in lean cruise mode.
If you put the car in open loop in the tune it wont correct the fuel at all, it will only be running of the data in the fuel tables.
