mpg readout
- Thread starter johnd
- Start date
johnd
Members
Interesting explanation CJ. Presumably based on fact and not inspired guesswork?
Now a question: if you are sitting at traffic lights with your foot off the throttle, you are in principle doing zero mpg. Whereas going downhill with your foot off the throttle gives infinite mpg. So the throttle pedal position is not always giving the correct mpg, is it? Methinks there has to be a bit more intelligence in the system.
Now a question: if you are sitting at traffic lights with your foot off the throttle, you are in principle doing zero mpg. Whereas going downhill with your foot off the throttle gives infinite mpg. So the throttle pedal position is not always giving the correct mpg, is it? Methinks there has to be a bit more intelligence in the system.
Perhaps John this is where the computer is not 100% but you have to give at least a 5% either way in my book.
johnd
Members
Agreed!
Dan Robinson
Grand High Plumber
I shall consider myself Pounced Brett.
John, I suspect that is where the abs comes in measuring wheel sPeed.
John, I suspect that is where the abs comes in measuring wheel sPeed.
Great explanation CJ and I learnt something too.
However I stick to my original point - the computer doesn't get it right (not even nearly right). Best stick to the old fashioned way and do it manually.
However I stick to my original point - the computer doesn't get it right (not even nearly right). Best stick to the old fashioned way and do it manually.
I still think it has more to do with injector 'on' time because if the MPG was calculated purely by throttle position, how could the system compensate for ambient temperature/ pressure differences ie. engine requiring more fuel in cold weather due to the air being denser? just my opinion...Ok this is pretty simple but need to understand all the components and logic behind it .This is applicable to petrol preface lift 2.4 and facelift 2.0 and 2.4 , as for diesel who bloody cares.
The entire system is called ETC aka in the Honda world as the Electronic Throttle Control
The two major components in this system are the APP aka Accelerator Pedal Position Sensor and DBW Drive by wire.
What is APP ? This replaces the mechanical linkages between the accelerator pedal and the throttle, but the APP still uses a wire to give the driver the positive progressive feel and feedback. With the big organ sizes pedal and wire you got to admit the pedal feel on our car is spot on. Now to make the mechanical changes from the pedal understandable in volts to the ECU the APP is piggybacked on by the APS aka Accelerator Position Sensor.
The signal from the APS is proportional to the accelerator position being fed by the wire and gives the corresponding volts to the ECU how much to open and close the engine throttle.
What is DBW
The drive by wire unit consists of a TA aka Throttle Actuator and TPS aka Throttle Position sensor The APS is feeding info to the ECU which in turns feeds the TPS which tells the TA how much the throttle should be opened in respect to the APS. DBW unit is driven by a little DC motor which is a fed info directly from the TA. Inside the car under the dash you have the Throttle Actuator Control module relay & Throttle Actuator Control Module. This module enables data logging on the ECU.
Now how does this mileage calculated then?
When the engine is idling the ECU controls the TA to maintain the proper idle speed according to engine loads. When the accelerator pedal is pressed the ECU open throttle valve depending on the APP and APS sensor signal. This data is constantly being logged on ECU.The base MPG is purely calculated on throttle positioning. Use less of that throttle you will get higher mileage, do down a hill with no throttle you will see the GUI displaying 100 MPG the minute you touch it is comes down quickly.. Hence the huge variation in city driving and cursing on the motorway.
ETS is a very complex beast which heavily integrates with three core area namely ABS & TCS Traction Control System & Side slip control to make up VSA , that for another thread which is very interesting..
+1 And think of it this way, if fuelling was just down to throttle position why have an ECU, how would remapping work? Throttle position is part of it, but other factors are taken into account. The amount of fuel injected in either petrol or diesel engines is a complex equation, air temp/engine temp/load etc etc. Injector dwell and fuel pressure are certainly the main parts of the calculation to get the amount of fuel used. Then fuel trim has to be thought about.
I see the on board trip computer as an mpg estimator. Mine was fairly accurate prior to remapping, and as I switched between standard map and Stage 1 quite a few times when looking into the smoking problem, I can say after remapping its much more optimistic, probably because they have reduced the air fuel ratio from the standard Honda values, and this throws off the mpg calculator.
Maddog beat me to it. I've been thinking about this all morniing. The only way an ecu can even come close to getting the mpg value correct is by knowing how much fuel has been used, regardless of other parameters i.e temperature, over a certain distance. Honda must know how much fuel passes through a brand new injector at a certain pressure. This would be a simple equation for an ecu to calculate. I would have thought the inaccuracies come in because the injectors and pressure sensors are not perfectly calibrated, and become worn over time. Just seems logical to me, but could be wrong.
just out of interest, if diesels don't have throttles, what controls the amount of air the engine takes in ?
I just googled it, it seems diesels don't need to control the air intake....oh well, learn something new everyday :blush:
Dan Robinson
Grand High Plumber
The laws of physics have their uses matey :lol:
johnd
Members
Now I wonder, would the airflow/temperature be directly proportional to the amount of fuel injected? Answers on the back of a postcard......
yeah, nothing like trying to keep twin SUs or twin webers in tune :wub:
johnd
Members
Yeah, like my first car - a 1932 Austin 7. 0 - 30 mph in 5 minutes....... :blink:
or like my last carburated car 1/4 mile in 12 sec @ 108mph
FarHanSolo
Members
As an aside, is it just me who got 701 miles from one tankful or are you going to beat that peeps?
kpanchev
Members
And very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very, very LATE!!!!!!
Well you keep saying that mate, but really you end up at your destination maybe 10 minutes later but more relaxed. Our minds are automatically programmed to get to our destination as quickly as possible, but given the state of our motorways, you can make steady economical progress sat in the 1st lane at 60mph and get to where you're going not much later than the plonker weaving in and out of lanes trying to do triple figures speeds all the way. You're almost guaranteed to hit traffic jams at some point in a 130 mile trip and any progress you've made by speeding is just cancelled out.
Don't get me wrong, I don't sit in the 1st lane at 55-60mph but it was interesting experiement with surprising results for me personally. Just have some decent music in your cd player :lol:
Don't get me wrong, I don't sit in the 1st lane at 55-60mph but it was interesting experiement with surprising results for me personally. Just have some decent music in your cd player :lol:
kpanchev
Members
Well, I do understand that, but my problem is that I tend to crash if I drive slowly... I get bored and start to get distracted or fall asleep... 
.... When I do long journeys (more than 5-6 hours), I tend to cruise at different speeds just to break the monotonous drive... It's very refreshing after 20 mins of 70 mph to do a 20 min blast of 90... or 100... or ...
.... When I do long journeys (more than 5-6 hours), I tend to cruise at different speeds just to break the monotonous drive... It's very refreshing after 20 mins of 70 mph to do a 20 min blast of 90... or 100... or ...