Can someone explain "lean cruise"?

[BJM]

The new Extender chips have this feature. I am trying to figure out how this works. I thought the ECM could only tune around stoichiometric values. Somehow someones figured out a better way I guess.

 

[TurboDave]

Yes, someone has figured a better way.

What's done (in a nutshell) is in the chip, where all the parameters are setup for the limits of what the ECM assumes to be stoicheometric, are changed to leaner values. It basically is told to look in a different location for the new limits, and use them as stoicheometric during the times when "lean cruise" is set to operate.

 

[U1ARUNIT]

While we are on the subject..

I have the latest Extender rev E with this feature and currently have it enabled. I am just wondering why anyone wouldn't want it enabled? Are there any downsides to using that we should be concerned about or times that it should NOT be used? Does running this lean setting for long periods shorten motor life etc..?

Thanks!

 

[TurboDave]

Originally posted by U1ARUNIT
While we are on the subject..

I have the latest Extender rev E with this feature and currently have it enabled. I am just wondering why anyone wouldn't want it enabled? Are there any downsides to using that we should be concerned about or times that it should NOT be used? Does running this lean setting for long periods shorten motor life etc..?

Thanks!

I don't know of any downsides. The engine's just running a little leaner down the highway during cruise modes (verfied by my EGT meter). It's not running as lean as today's modern systems!

 

[bruce]

Lean mixtures, burn very slowly, unless your using a high turbulence cylinder head.
So to recover as much energy as possible from this leaner mixture, you have to run more timing.
Lean and more timing, means heat.
Right opposite the piston dome is the crankcase, and the oil. So the oil runs hotter.

I used to think lean cruise was a good thing, until I actually tried a lil richer then 14.7 with a whole lot less timing, ie about 1/2 as much. My oil pressure is higher, and sustained ventures to worp speeds are no problemo.

Same for the guys that disable the EGR, without retarding the timing, EGR slows down the flame in the chamber so when you don't run it you don't need the extra timing.

I've run 30 MPG, and I can run 25.
I'll stick with the 25 and keep the motor happy.

 

[U1ARUNIT]

Thanks!

Bruce,

Thanks for the explanation, that was the info that I needed to know.

Regarding EGR operation, I have it disabled and welded closed on my motor and with the Extender is not used so we should be okay there. I noticed that it never commands any duty cycle for EGR on Direct Scan at least. I would imagine that Bob has compensated in the timing tables for the lack of EGR. At least it seems so since the car no longer exhibits part throttle knock like it did with previous chips that commanded EGR (and higher part throttle timing).

For now I think I will go back to the "regular" cruise programming. Fuel mileage is still VERY respectable even with the Seimens 55's and drivability has NEVER been better. One thing is for sure, Bob has done his homework with the Extenders.

 

[bruce]

Re: Thanks!

Originally posted by U1ARUNIT
Bruce,

Thanks for the explanation, that was the info that I needed to know.

One thing is for sure, Bob has done his homework with the Extenders.

Your welcome,
yep, it takes alot to improve on any of Bob's offerings.