Hi, I'm a new member. I've been reading this great site for awhile and have used many of the tips here with great success on my 2004 HCH. I have a question about Lean Burn mode.

I recently took a short day trip from Eugene, OR to Portland, OR. It's about 120 miles along I-5, almost entirely flat and straight. On the trip up in the morning, the FCD averaged about 55-60MPG and everything was working as it usually does. I was driving about 65-70MPH (I know this is not the ideal speed for fuel efficiency, but I tend to fall "middle of the road" in the speed vs. efficiency trade off).

On the return trip in the afternoon, I was really fighting to have the FCD register 40MPG. I had backed off my speed somewhat (was going about 60-65MPH). I was hard pressed to figure out what had changed. My assumption was that (for whatever reason) the car wasn't entering Lean Burn mode (I'm assuming Lean Burn is when I'm cruising at a stable speed and the FCD will jump up to around 60MPG). Whenever I forced the FCD to about 50MPG, I would slowly (and continuously) loose speed. This was very different than the car's usual performance, and certainly different that the morning's trip up.

I can only come up with two possible reasons: 1) I did seem to have a fairly strong head wind on the return trip (which meant that I probably had a tail wind on the trip up). 2) There was a LOT of field burning going on during my return trip (as usually happens this time of year in the Willamette Valley). So much, in fact, that the air smelled quite smoky (I had to re-circulate the cabin air most of the time to avoid the smoky smell). Could the added smoke in the air cause that much decrease in efficiency?

My particulars: 2004 Honda Civic Hybrid, CVT, 2200 total miles. Econ button always on. I try to practicing the "drive with load" technique, rarely use cruise control or A/C. I bought the car on 6-9-04. Lifetime MPG is 46.5, current tank is 47.6. Factory Dunlop tires at 45PSI.

I've been quite happy with my car and realize that 40MPG is still a great number, I'm just curious about what could have caused the decrease in efficiency. Any info would be appreciated, and sorry for the long post. Thanks,

Garrett
gar1138

BTW, does anyone have any info about the particulars of Lean Burn mode? I think there was a thread about it at one time, but I can't seem to find it.