Question about Miles/Gallon readings

mlheck · Feb 22, 2017

So I'm chasing a MPG issue and have replaced the thermostat. During my test ride today (during February, AWESOME), I changed the display to instant MPG and noticed that the display was lacking behind my throttle inputs. I was having about a 20-30 second delay between throttle inputs and display changes during my ride. Now I have never used this function, so I don't know if this normal and that is what I am asking. In all of the other vehicles I have owned, the instant MPG gauge was basically a vacuum gauge. This was way to slow for a vacuum gauge, but I know how Honda loves to play with the information we receive from our gauges. So I asking if somebody else can try their instant MPG display and see if it has the same delay. If not, then I guess that I need to check the vacuum lines to the MAP sensor. The sensor itself costs $135.95 so I'm hoping to avoid that cost.

Thanks,
Mike

Kevin_56 · Feb 22, 2017

Big delay. It is no where accurate, neither is the average MPG. Fill up, reset trip meter, fill up and divide your miles by gallons used. Only way to check your MPG.

ST Gui · Feb 22, 2017

I believe that's normal. It still needs some time and distance to calculate 'instant' mpg.

Igofar · Feb 22, 2017

Kevin_56 said:
Big delay. It is no where accurate, neither is the average MPG. Fill up, reset trip meter, fill up and divide your miles by gallons used. Only way to check your MPG.

Igofar · Feb 22, 2017

mlheck said:
So I'm chasing a MPG issue and have replaced the thermostat. During my test ride today (during February, AWESOME), I changed the display to instant MPG and noticed that the display was lacking behind my throttle inputs. I was having about a 20-30 second delay between throttle inputs and display changes during my ride. Now I have never used this function, so I don't know if this normal and that is what I am asking. In all of the other vehicles I have owned, the instant MPG gauge was basically a vacuum gauge. This was way to slow for a vacuum gauge, but I know how Honda loves to play with the information we receive from our gauges. So I asking if somebody else can try their instant MPG display and see if it has the same delay. If not, then I guess that I need to check the vacuum lines to the MAP sensor. The sensor itself costs $135.95 so I'm hoping to avoid that cost.

Thanks,
Mike

I can't recall seeing a MAP sensor switch go bad, however, I have seen MANY ST's have their vacuum lines and 5 way tee clogged up.
In a good running state of tune, I get mid 50's as far as mileage goes, but to get a correct reading you should really do as Kevin_56 said, and fill up and use your trip meter etc.

Dave.David · Feb 22, 2017

I did read on this forum somewhere that the instant mile per hour gauge samples every 20 seconds

mlheck · Feb 23, 2017

Kevin_56 said:
Big delay. It is no where accurate, neither is the average MPG. Fill up, reset trip meter, fill up and divide your miles by gallons used. Only way to check your MPG.

I'm not concerned about the accuracy of the MPG it is showing for that reason. I was concerned about the slow reaction time causing fuel mixture issues.

ibike2havefun · Feb 23, 2017

mlheck said:
I was concerned about the slow reaction time

Nope it's a sampling rate thing as Dave.David responded. Page 25 of the 2003 model owner's manual states the display updates every 15 seconds, for both momentary and average fuel consumption rates. You just don't notice it as much on the average since that changes much less rapidly, and over a smaller range once it has begun to "settle" after a fill-up.

mlheck · Feb 23, 2017

Thanks for the info. One less thing to worry about now.

Blrfl · Feb 23, 2017

Igofar said:
I can't recall seeing a MAP sensor switch go bad...

It has happened a few times. Not as often as the plumbing gets gunked up, but it has happened.

--Mark

mlheck · Feb 23, 2017

I am very much aware of how the average MPG works. I don't take its output for gospel, but use it as a tool to keep me aware of any issues that will affect engine performance. This is how I learned that I had a thermostat issue before the 2 bar display started happening.

I've never used the instant display, so I was not aware of how it gathered it information.

I do plan to give the 5-way and connected vacuum lines a once over though next time I'm in the neighborhood.

Thanks everyone for the info.

Dave.David · Mar 2, 2017

Any word on a update for the mpg refresh rate?

JimGregory · Mar 3, 2017

Dave.David said:
Any word on a update for the mpg refresh rate?

Update? Not likely to get one Dave. It is what it is.
Personally I think it exists just to annoy me.

Dave.David · Mar 3, 2017

JimGregory said:
Update? Not likely to get one Dave. It is what it is.
Personally I think it exists just to annoy me.

You are not alone on that.

Savago · Mar 13, 2017

@mheck: mine does the same thing when using the 'real time' mode.

The average gas mileage is a bit off too (reports worst gas mileage than the one calculated by filling the gas tank and diving by logged distance) e.g. reported 39 mpg, I calculated 42 mpg.

STmark1300 · Oct 9, 2021

Igofar said:
can't recall seeing a MAP sensor switch go bad, however, I have seen MANY ST's have their vacuum lines and 5 way tee clogged up.

I have had trouble with my cruise control, and recently my MPG gage is stuck on 35mpg. Could my problems all be the 5 way tee?

mjc506 · Oct 9, 2021

What problems with your cruise control? (probably better for its own thread, though)

The MPG number is calculated by the dashboard - it receives a signal from the ECU when the injectors are open, and from the VSS from which it can track distance travelled. It knows how much fuel flows through the injectors per second* so can calculate fuel used, and miles travelled over a certain period (I think 20secs is about right for the 'instantaneous' display). The MPG display isn't driven from the MAP sensor, and has no bearing on how the bike runs (but of course if affected by how the bike is running

, so a blocked 5 way tee, stuck thermostat etc can/will affect MPG, which is then reflected in the display)

I don't think anyone would advise you not to check/clean the tee and surrounding hosing etc, but I wouldn't expect doing so to solve your issues.

*More accurately, probably fuel quantity per millisecond or smaller, with an adjustment for opening/closing time. This will be based on clean, new injectors at a certain fuel pressure; so changes in fuel pressure, dirt in the system, worn injectors , even different fuels etc etc will all introduce error which the dash can't account for, hence the variation in accuracy across bikes.

STmark1300 · Oct 11, 2021

Thank you.

Question about Miles/Gallon readings

mlheck

Kevin_56

ST Gui

240Robert

Igofar

Igofar

Dave.David

Rider

mlheck

ibike2havefun

Still above the sod

mlheck

Blrfl

Natural Rider Enhancement

mlheck

Dave.David

Rider

JimGregory

Dave.David

Rider

Savago

STmark1300

Ron

mjc506

Matt

STmark1300

Ron