Quote:
Originally Posted by extragoode
This is a little off topic too, but for engine that already have the fuel cutoff it would be nice if there was a way to manually switch it to lower displacement. My mother in law has a GMC Yukon with the flex fuel engine that can switch from 8 to 4 cylinders, but she complains that it still gets horrible gas milage. So a couple weeks ago, I got the opportunity to drive it and was ready to see what I could do with it since I figured she was heavy footed with it. It NEVER switches unless the vehicle is COASTING. I used the cruise on flat ground all the way down to 45mph and it still never switched. Anything below 45 and the TC unlocked.
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I completely agree. I had a chance to drive Chevy Impalas / Montes with every engine option over the last 7 years -- this included the 3.9L V-6 "LZ8 and LZG", and the 5.3L V-8 "LS4 with AFM" (active fuel management or cylinder shutoff).
The LZG had the E85 option, which was noted to disengage cylinders more frequently with the additional power, but was very inefficient with the ethanol. With the standard AFM LZ8, it was tough getting 3-cylinder mode to engage (a dash-display showed when it happened + you could feel it). It helps in the city a little bit, but get out on the highway at 70 MPH with a headwind, and it does nothing. It was noted from the SG that 50% load was the basis for the algorithm.
The conclusion was that it did nothing but add weight and cost to the model:
3.9L----------: 24.3 MPG
3.9L with AFM: 24.9 MPG
5.3L with AFM: 22.0 MPG
On a side note, the 3.5L base without E-85 capability averaged 28.7 MPG. The E-85 capable engines have a larger fuel tank and a bit more overall power -- 26.4 MPG without E-85, 21.4 MPG with E85. ~E60 was 23.1 MPG
RH77