I know people say you can do a new A/C without a retune...that's not what this thread is about. (If that's what you're looking for...search...pleanty written here about it already.)

When I got my 2011 FXDWG, I noticed fuel milage left a lot to be desired. I ride 42 miles, one way, to work every day during the week. While it was still a lot better than my truck it was worse than my Sportster 1200 conversion. On that bike I was used to getting about 150 miles to a tank...3.3 gallons. That worked out to roughly three one-way trips either to or from work. On my Dyna, I was seeing about the same milage but on 4 gallons. I thought with the 6th gear they would do better than that.

Then I saw that the more I rode the better milage it got until at about 4-5K miles I was getting much better milage...about 180 miles to 4 gallons. Now I could make four one-way trips to work. The salesperson and most on here confirmed that, on a new bike, milage improved as the engine broke in.

I'm now starting to question if that's the reason why.

A couple months ago I put a new A/C on my bike and did not retune the ECM. It breathes much better than the stock air cleaner and the initial drop in fuel milage back to what I was getting when the bike was new seemed to be the price I'd pay for the slight increase in power and response.

However, now about 4-5K miles later, the bike is getting BETTER fuel ecconomy than it did before. This is fairly typical with cars when you go to a better breathing system that, if you stay out of the gas, milage improves but I had heard with bikes this wasn't the case.

The other day, for the first time, I got five trips out of a tank...207 miles. I filled up and took on 4.4 gallons. I had gotten about 20 miles more out of the same amount of gas as I ever had on the stock air filter.

So I'm wondering if it's not the "break in" that gives us better fuel ecconomy but rather the ECM "learning" how the engine behaves at different RPM levels. Perhaps it starts out rich and then slowly leans to optimum. That's what the data seems to show. Since the ECM "guesses" what the fueling should be then "checks" to see if guessed right by looking at the O2s it would make sense that it would be programmed to error on the side of rich.

My theory is, when I changed air filters the ECM recognized that it was "guessing" wrong and seeing a lean condition so it reverted to "guessing" rich again and took another 4-5K to "re-learn" the increase in the amount of incoming air. Again, I know EFI systems in cars can do this and there has been some debate as to how much our bikes can do this.

While without the retune the engine is going to run lean...it seems that it's going to run no more lean than it did with the stock A/C. Anyone have any thoughts on this or have seen the same kind of "learning" from the ECM?

 

I would be careful running that way. My local ALR group road capt ran an Arlen ness intake and stock pipes on his street bob. Rode it 8k miles till it quit. My 2cents worth at least!

 

On my Limited I first ran the SE Ventilator intake and rush slip ons, which Rush themselves told me was ok, and in less than 300 miles my right side pipe was completely gold and I had to trash it, my fuel mileage got worse, as did the heat under my leg. I would not recommend it. The bike got leaner too as if that was even possible, lol.

Whenever anyone ask me, I just tell them to save the $$ and do it right, it will save you $$ in the long run.

This was my experience anyways.....

 

OP...if your ECM was re-learning, 4k-5k miles seems excessive for that process to take place. Doesn't it seem that way to you? As for break-in, that happens pretty quickly. Most dealers advise you to "take it easy for ~ the first 500 miles". The rings seat much sooner than 500 miles.

I can't offer a reason why you seem to be getting better mileage. Maybe you're riding style has changed subconsciously which might attribute itself to better mpg?

The only way to truly know the answer is if you had a "snapshot" of what your ECM looked like the day you brought it home vs what that snapshot looks like today.

 

On my old 1991 jeep ECM it would relearn the fuel-mix ratio after 40-50 starts before it would find optimum performance/mileage. Is 40-50 starts about 4-5k miles?

 

Doesn't seem like it could "learn" very much from a narrow-band o2 sensor.

 

You may have a point here.

 

At the risk of oversimplification, using stock NB sensors, the ECU can readily and accurately learn what it takes to get the fuel to its factory AFR/Lambda set point, or it should throw a code. If you are trying to reach a AFR/Lambda, out of the NB sensor range, say 14.2 to 15, then its not so good. (we all know having a good tune is more than just setting a few AFR points)

It usually takes several on/off cycles and perhaps 500 miles to get to a relatively close and steady state, but I dunno if 3-5000 miles is unreasonable to expect. I know if the ECU has to make that much correction for cruise, the other operating ranges may be pretty far off.

I would guess that if you can correlate quality of fuel, riding temperatures, time of season to the variation in mileage you may find something else.

But yes the ECU will adapt/learn and adapts very well when cruising, and if you are happy the way it runs otherwise, you have a keeper. Don't fix it if its not broken, IMHO.

 

ColdCase, I understand what you're saying but for the ecm to read the data from the o2 sensors doesn't the system have to hit a 14.7afr first? That's fairly lean. Once that happens what other data within the ecm tells it to make corrections for? There has to be another piece of data it follows, because if it's the 14.7, that's just too lean. Correct (sort of)?

With so much contradictory info out there I'm just really interested about this. Also didn't the moco update the ecm on the later model delphi systems to be able to correct more efficiently? My 07 wouldn't "learn" as well as say a '10 or '11, right?

 

The reason for the fuel mileage? You say the engine breaking in but what about the belt loosening, the wheel bearings/seals, the thansmission bearings/gears, the tires getting smaller/harder with less cushion, the brake pads wearing in, ect. The engine is only part of the equasion. The bike just coasts better/longer once everything is broke it. Split hairs? Yeah. How about the oil/grease viscosity in warmer weather? Jump down to a 10/30 synthetic and up 10 lbs in your tires. Bet you see another 5 mpg. The oil thing cannot be good for your engine though. Bet you're not a Nascar fan. They do all kinds of crazy stuff for qualifying and restrictor plate tracks.