A friend of mine told me when he was changing the exhaust on his soft tail he was told he had to re map his puter. Why does this have to be done if the puter adjusts the fuel mixture by reading the 02 sensor. A bike mechanic from a indy shop told me it was a scam by HD, he told me the O2 sensor should read the change and adjust the mixture, my buddy has 18k on his bike since he changed the entire exhaust system and it runs fine, plugs look good, no problems, so why the re mapping? I understand it should be done on a carb bike but with puter controled injection with the puter reading and adjusting the mixture why?

 

Simple answer, narrow band O2 sensors. The puter has a relatively small range of adjustment, there are plenty of people who think its a "scam" and that the EFI self adjusts, but thats because they have never observed WBO2 exhaust gas analysis after a component change. They are just regurgitating the myths that they hear from others they have confidence in.

 

Like all computers, his bike's ECM has a maximum range it can analyze and make adjustments. Outside those ranges and the computer is just guessing.

And like all computers, the bike's ECM can perform one function at a time. Yes, it does this pretty fast but one at a time regardless.

The heart of the ECM parameters are the VE's (volumetric efficiency) of each cylinder. There's a formula for figuring an engine's maximum but things like air filters, intake manifolds, cylinder head design, cams, and exhaust systems have significant affects on the actual VE's of a particular engine.

The closer the map is to actual conditions the quicker and more efficiently the ECM will use that data and respond.

So, it's possible to get a map so far out that the bike won't even start. It's also possible to get the map to burn fuel so completely that the heat generated can cause damage to the engine.

IMHO, it's worth spending the time, effort, and money to get the map close enough for the ECM to do as little work as possible.

Then, generally speaking, both the bike and rider is happy.

 

Do you have to?: No
Do you need to?: No
Would it be better if you did?: Yes

 

Pine Tree did a good job of explaining why you might want to invest in a tuner, but I'll add my 2¢ to what he said. One reason to re-tune after making changes (mufflers, AC, etc.) is that the O2 sensors work only in a narrow part of the operating range, called "closed-loop" area, mostly at idle and in the cruise range. Above that in the other half of the operating range is the "open-loop" area, and that is where the O2 sensors are not functional.

The O2 sensors will still work in the closed-loop area with changes in intake and exhaust, but since the airflow characteristics are different they'll have to work harder by operating in a wider range. They work efficiently only in a narrow range very close to stoich (14.68:1 AFR), and mostly act as switches to keep AFR at that point. Get them out of their comfort zone and their accuracy comes in question. The right way to deal with changes in airflow is to get the VE tables (airflow) correct in tuning and let the O2 sensors work on a more level playing field--as well as get the open-loop area where it should be. Since the open-loop area is not dynamic, i.e. does not change with feedback from the O2 sensors, the old stock values in the VE tables are still there--and that will not be optimal when airflow changes.

You could leave the tune alone and change mufflers and AC, which would likely realize better overall performance, but it won't be optimal. Just uncorking the intake and exhaust with freer-flowing components makes a big difference by itself, and some inefficiencies in the tune will not totally negate that progress.

Some say you need a tune to lower AFR's (richer) which makes the engine run cooler. Making the bike run richer does make some difference, but in the tests I've made on my bike it isn't very much, and it will certainly make an impact on gas mileage, probably noticeable.

I hope this helps.

 

Was just curious, I did not know they programed them to such a narrow band, makes sense then, spending all that money for exhaust and intake stuff then not remapping seems to defeat the purpose. The mechanic at the indy place told my friend he did not need remapping and the puter would adjust, I will have to inform my friend of this info, thanks all for the help.

 

One of the best, most straight-forward explanations I have read about this on the Forum. Thanks ICLICK!!!

 

The purpose of the computer is to adjust running conditions between sea level and the highest mountain pass, desert heat and arctic winter. Those who claim it will adjust for alterations are actually using up some of that adaptability, which is not there for changing mufflers or air filters! Best to ignore them.

Our bikes are running on a knife edge, especially with air/fuel ratios, so they meet EPA regulations. That leaves us with two choices when tuning our bikes. Either retune to meet EPA, or adjust to optimum settings.

As a racer I'm sure you can appreciate the benefits of tuning a bike, even on the road, so it gives it 's best. It can't do that by making mods, then leaving it untuned!

 

Oh it's definitely a scam....for a couple hundred Harley could have added auto tune to their ECM's .....but then they would kill a pretty good cash cow....remap&dyno, remap&dyno, remap&dyno, remap&dyno, etc.

 

Excellent post, very clear explanation !