Lean Cruise

How-To add Lean Cruise to p01 ecu (haven't tried with p59...may also work??)

By Grady

Do this at your own risk...please don't blow shit up...and if you do, don't blame sloppy ;)

Lean cruise is an option that Australian cars received. It allows the pcm to command a fuel ratio more-lean than stoich. Leaner=less fuel=better mileage...that's the idea anyway. You'll find it's not exactly that simple...but here goes.

Here's a little background...if you don't give a shit, skip to the next paragraph. When it comes to the EPA, they care about the overall impact from your vehicle to the environment as a whole. A leaner fuel mixture burns with more NOx...aka bad gasses. A stoich mixture burns more cleanly. So, they had to choose...do they burn LESS fuel but with more bad gasses per volume fuel (lean cruise)///or burn MORE fuel but with less bad gasses per volume (stoich cruise). They opted for less bad gasses and more gasoline itself. Australia chose the other way...they opted for better mileage and worse NOx. Since the pcm was shared for gm vehicles between the US and australia (holden) the tables are there for the lean cruise feature...but they weren't used in the us vehicles.

DISCLAMER: Don't do this on road-bound vehicles...only do this on offroad, endurance based or mileage contest type vehicles. Now that we have that out of the way, here's how to make lean cruise availible on your US pcm.

First, Note your current system type. Trucks will usually be GMT800...don't forget your current system type. Next change your "system" setting to V...this is an Aussie system type. To breeze over the nitty-gritty, the PCM performs a checksum procedure and it uses the system type to determine what features to allow...setting it to V lets you get past the checksum and into lean cruise mode.

Once you've set the system setting to V, go into the "system options" tab and Copy all of the 1's and 0's from the original system type onto the V line. If you don't copy system options, you will have lots of issues with alternator, torque management, etc etc. Picture below shows your areas needing attention in the "system" tab

After you change your system settings, go to engine->fuel->lean/fuel saving

This is your lean cruise area for fueling. you can set delay parameters...use these to ensure lean cruise is only enabled when you want it to be. Enable/Disable speeds set a range that it can work in...the timers set the delay time for which the vehicle needs to be running and moving before it can enable. These times MAY be different. Enable delay needs to be longer than the moving delay. The enable delay is how long the engine needs to be running before these tables go active. The moving delay is how long you have to be moving before the tables go active. Use at your own discretion.

The "vs RPM vs Cyl Air" table is a SUBTRACTOR. This is how much to subtract from stoich ratio when in lean cruise.

Here's the math when these tables are active.

AFR=Stoich/(1-Subtractor)

Example...pumpgas with subtractor value of .100

AFR=14.7/(1-0.100)=14.7/0.900=16.333

So, in that example your commanded AFR would be 16.33

Larger number in the "vs RPM vs Cyl Air" table means more-lean AFR

The ECT table lets you choose to only allow lean cruise when up to temp. The multiplier acts on the subtractor table.

Leanout rate is how quickly these tables are ramped in/out.

The other factor of making this work is the timing. You can lean it out all you want, but if you're going down the road, it's going to take the same amount of torque to keep the vehicle moving. So, lean cruise should also be used with increased timing. You can do this by just altering your base timing table but the better way to do it is to use a spark adder table. See pic below.

This table is used to add timing as the AFR is leaned out. In the pic below, anything above 1.0 is stock for this particular truck. Anything below 1.0 was changed for lean cruise. As you can see, you can add additional timing for when you're in lean cruise mode. The top Axis is the current AFR multiplier...see the above math...this would be (1-your subtractor)

There ya go...pretty simple.

1. Change system type
2. copy system settings
3. alter fuel tables
4. alter spark tables
5. log log log
6. Repeat starting at step 3

I would recommend for a starting point you don't use the values in the pictures above. I recommend finding a tune file from a vehicle originally capable of lean cruise...and conservatively using its values. Then adjust to your liking from there.

Remember: Do this at your own risk...please don't blow shit up...and if you do, don't blame sloppy ;)