My new FR-S!

[MetroMPG]

Can you explain why it came on?

I think it comes from comparing the upstream O2 sensor against the post-cat sensor, no?

[serialk11r]

Originally Posted by MetroMPG

Can you explain why it came on?

I think it comes from comparing the upstream O2 sensor against the post-cat sensor, no?

Well, when the cat is cold, it's indeed not converting efficiently, and the cat was probably pretty cold from all the engine-off coasting. Probably comes from comparing the O2 sensors, not totally sure how it works. These newer cars have much cleverer ECUs and will pick up on this kind of stuff.

The way I see it, I'm saving a lot of fuel? lol

[serialk11r]

Just drove down the peninsula this morning and decided to shoot for maximum mpg just to see what this car could do. I took 101 not 280 despite the hills of 280 being really good for pulse and glide since 101 traffic moves slower and it's a slightly shorter trip overall.

Results:

Dash display read 40.0 mpg, odometer read 28.7 miles, actual distance travelled was 29.2 miles according to Google. That means there was about 0.5 miles of coasting that didn't get picked up by the odometer because the key was off. The mpg gauge doesn't count the miles travelled when the engine is off, and eyeballing the odometer (reads in increments of 0.1 miles) while the engine was off, I counted around 3 miles travelled with the key off, probably more like 3.5 but I'm not really sure.

By that calculation, the 40mpg was for around 25.5 miles or so, and the remaining miles I used no fuel, so the overall mpg was somewhere between 45 and 46!

I calculated that on just the freeway part I was averaging probably 43, but I did have to brake 2 times :/ Since I was using 101 which is mostly flat, I was just cruising in gear most of the time so there's definitely room for improvement there. The last leg around town though I had to be averaging something like 70-80 mpg thanks to my engine off coasting, and that's including several red lights and stop signs. Not bad

[serialk11r]

For some reason I had never thought to reset the mpg gauge to see how this car really does in city driving, so today I did, and the car indicates I was getting an appalling 20mpg while going through the stop sign ridden streets of SF, despite not exceeding 20mph and killing the engine diligently at lights. My MR2 could do ~25-27 under similar conditions. The extra 600lbs seems to be quite a burden.

That said, this morning driving up 101 into the city the computer said I averaged 40mpg, and I was doing a steady 65 with no engine off coasting. Seems to validate the 45mpg trip down as not being due to elevation change.

[Daox]

Still not too bad for a sporty fun car. There are a lot of econo boxes that barely eek out that mileage.

[serialk11r]

Going back to E85 blending to shave that few dollars off my gas expenditures. I just logged a 268 mile 3/4 tank that used 8.1 gallons for 33mpg, but I estimate that the key off coasting took a bit off so I'll call it 34mpg, about 80 of those miles were done on a ~25% ethanol blend. The dash mpg display seems to use the MAF + fueling table to calculate mpg so the numbers weren't any lower despite the car probably using a greater volume of fuel. I felt like the mpg numbers went up a tiny bit, since on some sections of freeway, the display would fluctuate between 39.x and 42 ish at 65mph on straight gasoline, and on E85 it would stay above 41. Totally not scientific though.

This full tank probably only has about 0.8 gallons of E85 in it, I'm going to add a little more tomorrow on the way back from work. Curious to see how my average mpg fares on E20. At some point I should probably start getting up a tiny bit earlier and going a little slower on the freeway to claw that extra few mpg back, heh. I can't get my commute above 35mpg while driving 65-70mph.

[serialk11r]

This fillup I went around 400 miles on 11.356 gallons, which means I was getting almost 36mpg overall!

I feel like I've hit a ceiling here, ~40mpg highway when I'm careful (~44-45 is possible if I stick in the slow lane doing 50, piss everyone off, and not have to brake a single time), and 25 when assaulted with stop signs at every block if I roll around super slowly. I'm pretty happy with this, but it's a little short of what I was hoping would be possible.

The highway figure could be pushed a little higher with a slightly taller tire, but these tires have tens of thousands of miles left in them. If I got a wideband emulator for the O2 sensor and had the car run lean, I imagine I could bump my highway average up a little and my city up by like 1 mpg, but 200 dollars buys a whole lot of gasoline.

I may try leaning out the fuel map a little more for city driving but it's not really going to save me much fuel.

[pgfpro]

Is this the engine that has 12.5:1 compression?

[serialk11r]

Originally Posted by pgfpro

Is this the engine that has 12.5:1 compression?

Ah, I abandoned further fuel economy pursuits and didn't see this. Yes, 12.5 compression, it's beautiful.

Thought I might share some updates, winter gas dropped the mpg by almost 10%, but I've ditched the commute, and been very diligently P&Ging every highway trip and city trip I take. I basically don't notice gas expenses anymore because it's a fill-the-tank-every-other-month thing.

I was targeting 20mpg instantaneous readout on the dash for my "pulses" but I just realized that's around 1g/rev load, which is running rich! I'm going to have to make a trip with stoich pulses to see if I can beat my fuel economy record.

[MetroMPG]

don't notice gas expenses anymore because it's a fill-the-tank-every-other-month thing.

That's neat. I'm in a similar pattern.

It bugs my family when I ask what local gas prices are doing... "YOU'RE SUPPOSED TO BE THE ONE WHO KNOWS!"