Came across this while playing around with GMECMEDIT. Just wondering if someone could explain what it is. Thanx.

 

I can give you a general rundown: It's a "lean cruise" mode. Under certain closed-loop conditions (like MPH above "x", RPM above "x", coolant temp above "x", load less than "x" etc.) the ECM can order up an AFR leaner than 14.7:1, to reduce fuel consumption. If used correctly, you can eek out another MPG or two during highway driving.

Jason

 

Ok, thanx for explaining that to me. Is it something you reccomend a newbie toying with or will I run the risk of making it too lean? Or is it not worth the effort to modify?

 

Being pretty much a newbie myself, I don't want to try to sound like an expert, but here's my thoughts:

Some codes use highway spark mode as well as a highway fuel mode. And some stock .bins have one or both enabled. Assuming that the rest of your tune is pretty close, your engine's not too radical, and you haven't gotten crazy with the spark advance and such, I think you could try the highway mode (using the enable parameters and AFR settings that are contained in stock .bins that use highway mode) without hurting anything. In all the stock .bins I've looked at, highway modes are only invoked under very limited conditions. There's also a "max time in highway mode" parameter that's usually set for 45-90 seconds.

That said, I think it's best to disable highway fuel/spark modes while you're tuning so as not to have "extra" things happening that affect your scan readings. Once you get everything else lined out, THEN play with highway mode if you wish.

Jason

 

To run lean cruise means having to run more timing since the lean mixtures take longer to burn.

That means putting extra heat into the engine.

On my car I've tired every combo of timing and AFR possible. I run open loop so I can easily pick what I want to run, and verify the AFR with a WB.

I have higher oip pressure, and at oil changes the oil still looks almost new. No longer is that black almost sooty looking stuff.

IMO, it's better to get better life out of the oil then saving a little in gas.

 

Ahh, light goes on again.

Bruce, did you say on an earlier post that you actually program light AFR for light load, as a substitute for highway mode?

If so, did you do this trial and error, as above, at cruise?
John