Fuel Consumption Sensing
Fuel Consumption Sensing
(OP)
I rented a luxury Buick on a business trip the other day, and in addition to XM radio and lots of other goodies, I noticed it had a real time readout of fuel consumption in MPG. Does anyone here know what sensor is used to calculate this? ie fuel flow, fuel weight, etc etc.
Also, are there any retrofit kits available for older cars that the average shadetree guy such as myself can install?
Thanks,
lighterup
Also, are there any retrofit kits available for older cars that the average shadetree guy such as myself can install?
Thanks,
lighterup





RE: Fuel Consumption Sensing
RE: Fuel Consumption Sensing
In other words it's a calculation by the ECM, not a matter of sensing. Most OEM's are fairly accurate, and read within 1 to 3 seconds.
These days most add-ons are for marine or aircraft. Flo-Scan is one company supplying to them. J.C. Whitney used to sell them too.
RE: Fuel Consumption Sensing
Now days, this is done by adding up the time the injectors are open and measuring the distance the car travels. This is simple for the car manufacturer as all the information is already controlled or available on the various control modules within the car. On a modern car with modern fuel injection, to measure the fuel flow, you would have to measure the fuel flow at the incomming fuel line, and the return line to the tank, and subtract the two readings.
Now, some aftermarket computers that people use to modify their cars with turbos, nitros, wild cams, high-compression, etc. have the ability to display computed milage (as well as completely re-map their fuel curves, timing, etc). But, unless you're into working on your car a lot, have time and money to loose, and willing to break your car and fix it time and again, I would not suggest it.
Easier to buy a new car.
RE: Fuel Consumption Sensing
Fuel flow can be conveniently measured by totalising the fuel injector on time.
As both these signals will be available at the ECU, it not difficult to calculate and display instantaneous fuel mileage or economy, in either metric or imperial units.
RE: Fuel Consumption Sensing
RE: Fuel Consumption Sensing
RE: Fuel Consumption Sensing
Likewise a change in tire size away from the original will alter the reading too.
RE: Fuel Consumption Sensing
An alternative approach I have seen is based on the fact that:
Fuel Flow = Air Flow / Stoichiometric Ratio.
For a gasoline (petrol) engine, the stoichiometric ratio is 14.7.
The air flow is obtained by a MAF (Mass Air Flow) sensor, and it is available over OBD2.
If there is no MAF sensor, then the MAP (Manifold Absolute Pressure) sensor can be used:
Air Flow = C x RPM x MAP / Absolute Temperature.
Engine RPM, MAP (intake manifold pressure) and intake air temperature are also available over OBD2.
In this case there is a constant of proportionality that must be found by calibration.
References:
* http://www.omninerd.com/2006/07/16/articles/57
* http://en.wikipedia.org/wiki/OBD-II_PIDs
* http:
So much for all that. Now can anyone tell me if this method will work on a diesel engine? What is the stoichiometric ratio in that case?
RE: Fuel Consumption Sensing
I would also recommend not assuming that your engine is operating at the stoichiometric ratio at all times. This can be especially true of stratified charge engine, cold starting, etc.
As far as the diesel stoich. ratio, check out the link below. It has been discussed here before.
http://www
RE: Fuel Consumption Sensing
I'm looking for a fuel consumption metric that will work for petrol (spark-ignition) and diesel (compression-ignition) engines using only generic OBD2.
What about PID $04 - Calculated Load Value?
This is returned as a percentage.
Any better suggestions?
RE: Fuel Consumption Sensing
http://www.scangauge.com/
easy to install (in fact portable) trip computer. Very entertaining.
RE: Fuel Consumption Sensing
Its a little tricky using the calculated load. Calculated load is expressed as a percent of how hard the engine is working compared to how hard it can work at a given RPM.
It should also be noted that for a MAP system, this load value is based on vacuum only. A MAF system bases this on airflow and RPM. Thus the calculated load on a MAF system is more useful.
Isn't OBD great?
RE: Fuel Consumption Sensing
The ScanGauge web-site says that 99% of cars and light trucks report information on fuel consumption.
So I presume they are using generic OBD data.
But what PIDs and what algorithm?
And given the variations between petrol/diesel and MAF/MAP vehicles, what accuracy is possible?
Quote from http://www.scangauge.com/support/faq.shtml:
"Can I use the ScanGauge II to save fuel?
If your car reports information on fuel consumption (99% of cars and light trucks do), and you use it to adjust your driving habits, you can save a lot of fuel."
RE: Fuel Consumption Sensing
According to ISO 15031-5 (equivalent to SAE J1979), for petrol (gas) engines the CLV is effectively (current airflow / peak airflow), and as reidh pointed out, the air-fuel ratio is not always stoichiometric.
But it goes on to say:
"Compression-ignition engines (diesels) shall support this PID using fuel-flow in place of airflow for the above calculations."
Of course, as with everything else in OBD, whether the engine manufacturers abide by the standard is another matter...
RE: Fuel Consumption Sensing
I think benkinsella perhaps can help me ....
I ´ve an instant fuel gauge lts/100kmts on bmw 520i 1988.
I want to convert the voltage at the instrument
(this is the ready product of compute the fuel consume
and the distance)
by a factor in order the scale gauge 0 5 10 11 12 13 14 15 ....
correspond directly to kilometers by liter
So when i read at 180 kph 5 this will be 5 kmts for liter and not 5 lts for 100 kmts.(of course presently it indicates 20 lts for 100 kmts).
I know the formula to convert it by how can i do to convert electronically the voltage for the factor?
I hope this operation will be possible with discret ic's and not with a programable microprocessor like pic ....
This is the idea then i will be more specific.
Thanks and congratulations for your level.
RE: Fuel Consumption Sensing
I don't think your question is particularly relevant for this forum, but I will attempt an answer.
If your gauge readout is analogue, with a moving needle, then you don't need to "convert the voltage" at all. Just print a new scale for the gauge and stick it on top of the existing one.
If your gauge readout is digital, with an LCD display, then first of all I would double-check if there is a "voltage at the instrument". It may have a digital interface, in which case you need something like a microcontroller.
If your gauge readout is digital, with a voltage input, then yes, you could use an op-amp circuit to perform a conversion, but would it really be any use?
Chances are the gauge isn't doing a straight-forward analog-to-digital conversion. There's probably a microcontroller in there too, with a look-up table or scaling factor involved. You would have to take the instrument out of the car, connect it to a programmable voltage source, and play around with it to be sure.
e.g. See the Difference Amplifier here:
http://www.phy-astr.gsu.edu/nelson/AN-31.pdf
If your input range is 0 to 5V, then choose V2 = 5V, and R1 = R2 = R3 = R4 = 10k.
Then when V1 = 0V, Vout = 5V, and when V1 = 5V, Vout = 0V.
That gives you the "reciprocal" function you're looking for, but that's only part of the solution.
RE: Fuel Consumption Sensing
"I don't think your question is particularly relevant for this forum, but I will attempt an answer ..."
Sorry i thought like this have relation with real time readout of fuel consumption ..and perhaps anyone
should have the same problem for best check the results of his experiments with cylinder deactivation, acetone,
EFIE diy and sensors trickings in order to get particular car save gas like mine....
"If your gauge readout is analogue, with a moving needle"
Yes it is!
", then you don't need to "convert the voltage" at all.
Just print a new scale for the gauge and stick it on top of the existing one."
Not i don´t want this way!
I want to change internal electronically speaking ...
I see exits a direct inverse relation, (inversor circuit), but the problem is that the scale don´t have proporcional steps....
and i thinking now with your info that, with a basic microcontroller with a look-up table should be the correct solution.
I´m only a hamradio, electronic and automotive enthusiast i appreciate your help and like valious info about op amps
should you have the kindness to tell me where go to get help or this exactly electronic basic microcontroller design to convert
volt input table to volt ouput table?
No bother more, and go away..
Thankfully for your valious information.