I don't know how your OBC shows such high mileage

 

My last tank netted 31.3 mpg and that was actually a mix of 93/89 and I gassed up today after work and topped off with 93 (little over 5 gallons) and got 29 mpg, same drive, everything. I wonder if the use of 89, combined with my CAI during the winter monthes is the ticket. Maybe the 93 lets the computer run too good with my intake, thus using a tad more fuel. This thread has been very interesting and has had some good reading and info, so what do you guys think about this. Now it has been very, very cold the past 2 days but to offset that I've only let the car run about 2 minutes before leaving out, factor that in too.

 

I am getting better mpg too, I have regular oil in there and idled about 1 hour warm up in 6 days of work. I got 33 mpg and thats not too bad considering the temperatures this week. Your cold air is hurting your mpg. The colder the air the MAF adds more fuel. I did drive a few short trip from the hospital to my parents house and the mileage on the scangauge was 25. So short trips with lots of stop and go really hurts mpg.

 

It would seem to me to me that the lower air intake temperature would only have a negative effect during warm up... Once underway the A/F ratios will be the same as at any other time the car is driven but would require a small percentage of throttle opening due to the increase in oxygen in the colder air... A certain amount of exhaust heat is necessary for the catalytic converter to work properly and to accomplish that it would be necessary to lean out the A/F ratio and (or) retard the ignition timing....I am just thinking out loud so make what you can of this post... Classify what doesn't make sense as brain farts since I have much less experience with the cold weather extremes you folks do... I have melted spark plug electrodes and burned a few exhaust valves on air cooled VW engines and British motorcycles in sub freezing weather though.

 

The MAF is a hot wire that is cooled as air comes in. The more current it takes to heat the wire the ecu knows how much air is there and adds fuel accordingly. The problems is when the cool air kit cools the cold air and allows for more air to enter, more fuel is required for a proper burn. My AIT air intake temps when moving are lower so more fuel is added. When stopped it goes up a little. Also there a correction for engine temps so even more fuel is added to get it warmed up. Then you have ethanol which doesn't start burning until the motor is almost warm. Ethanol just exits the exhaust and thats how it lowers emissions.

 

So it is essentially doing the same thing as us old timers did in the old days before ECUs and fuel injection except instead of choking the carburetor to richen the mixture by restricting the flow of air it is instead adding extra fuel to the colder denser more oxygen enriched air and will continue to do so even though the engine becomes warm.... The ECU should still have the same A/F ratio at operating temperature, make the same power at a given RPM but require a lesser percentage of throttle to be open to do so due to the density of the colder air.... A temperature reduction of 60 degrees on my car the way it is now is hard to imagine. The drop in temperature alone with the supercharger is like the difference between a stock engine and one with 5 PSI boost in 100 degree + plus.

 

It's all about choking the engine - automatically and variably to optimize the A/F and reduce emissions. I get confused in these threads because I run stock and the aftermarket goodies confound my understanding...

 

My OBC is still showing 31.7 mpg and its supposed to warm up to the upper 20's this week, a heat wave, so I'm looking forward to seeing the mileage go up.

But, is there anyway the 93 works against me in the cold with the CAI and the 89 helping out

 

Here is some info on dyno testing, it explains the sensors a little and how it effects the engine. Dyno Testing 101 – Measuring Performance | GruppeM North America

 

93 is not working against you, the ecu is not fully advance and thats why 89 runs better. Your mpg should go up next week, you need to look into the ultra gauge so you know what going on for your self. If its still available when I get my return I will get one too. I will give the SG to the wife if its better. It take muti tanks to set the fuel trims, there is alot of variables so running premium settles a few. I am happy getting 33 in my car, I drive mostly highway and at the speeds I drive at and the stop lights thats not too bad. I found a lot of info that I have to go through and will post as needed. 1 thing I read is that higher octane is need to run 14.7 A/F, thats probably MBT timing and using the least amount of fuel which is a compromise of best mpg and max HP. My dyno results proved that it runs at 14.2 across the rpm band, making the HP reading Honda said. 14.7 is not the highest HP but it is the best mpg you will get with government regulations.

 

MAF is a hot wire that the air entering the engine cools. How much it cools tell the ecu exactly how much air has entered. Just like the MAP sensor uses vacuum it is based on volumetric efficiencies. The IAT,MAF, coolant temps, the ecu knows how much fuel is need to make the car run right. Adding parts on there is adjustments from the correction maps to the programed map (that dont change) and they are stored in the Random access memory( a place that frequent used maps are used for faster access).

Your car as it ages the same thing happens its all stored in the RAM. So it doesn't matter the ecu still adapts to changing conditions. Some of the bad mpg is that there is no map and the motor is tuning it self so next cold spell there is info there to help get better mpg. Driving style has a lot to do with it too. http://www.autoshop101.com/forms/h59.pdf its ashame it alway Toyota that makes available the info. Honda has a similar advanced ecu and the fuel trims are similar too.

 

Thanks, I recently found that same site - lots of well presented info, yeah, too bad Honda doesn't share well.

Long/Short fuel trims as well.

 

This should explain close Loop and fuel trims. http://www.autoshop101.com/forms/h44.pdf

 

I wish I got to drive mostly highway to and from work SB, but I don't and trust me, I'm pretty happy with my mileage and appreciative for the advice on the use of BP Ultimate I'm just going to stick with the 93, the bump up to 31.3 mpg with the 2 tanks of mid-grade BP was probably a fluke and like I said, the perf was a bit different though, I did feel the trans shift a less firmly, so again, there is something to the use of Ultimate in my car, don't know if it does this for everyone elses ride, but it does mine

I can't wait for spring now, the Ultimate will surely pay BIG dividends!!!

 

Because you are auto trans if the weather is poor or fuel is not of a certain quality timing is pulled during and immediately after shifts.

This is the change in shift firmness you are experiencing.

I too have switched to BP 93 (no ethanol) in both the Fit and the Laser with positive results. I will be curious to see what happens when we switch back to summer gas...

 

Even though most of my ride is Interstate driving, its not necessarily the best for mpg. The reason is, its usually faster than optimum mpg and you usually never let off the gas. Ive tried the pulse and glide and the mpg comes up but not as fast as 45 mph with some lights. Time wise is 60/40 highway. You know that people dont drive 55 and going faster and slowing down will get you cut off just as bad as driving 55. I am getting around 35 mpg since Monday. Temperatures play a big part in mpg and with the Ultimate gasoline it runs better. Like you I cant wait for spring.

 

I haven't notice the timing pull except that after the shift the timing drops because the rpms dropped. But that might be because I use premium. I am looking forward to the summer gas as long as the temperatures dont go that high.

 

Timing advance should still be in the high 30's and 40's at low rpm in many of the load cells you would see under cruising.

If you were using regular you would probably see even less advance!

 

Agreed, it was 28 and when it change gears it went to 27. The timing curve is definitely MBT and 47 is the highest and WOT is 27 degrees. I remember when I had regular in there it was 20-22 at WOT. At light cruise on the Highway its in the upper 30s.

The biggest thing is the throttle body changing, If I drive hard its hard to get good mpg but after a day or two the mpg goes up under the same driving. I might have to look in to a Electric Throttle Controller.

 

31.4 mpg and I did notice that when I let the tank get below a half my mileage was over 31 by a little and when I filled up before a half it was down by 2 mpg's, any reason for this is it a coincidence

I did show 32.3 this week and back down a bit, but right now I'm showing about 31.8 mpg, I know the warmer weather is right around the corner, right