SGII MPG Calculation

[piekar]

i don't know if the scangauge can read the injector pw info, but it is available from the obd2 port

[monroe74]

Originally Posted by piekar

i don't know if the scangauge can read the injector pw info, but it is available from the obd2 port

Are you saying that OBD2 carries injector pulse-width info? Really? Are you sure? Because every OBD2 reference I've come across seems to omit that information (at least as far as the general OBD2 standard is concerned). Can you point me to a reference which indicates otherwise? It would be very helpful.

It seems that certain makers provide the info, but in a propietary manner that's not easy to get at. I think a helpful summary of the situation is here: http://www.mp3car.com/vbulletin/engi...ctor-duty.html

[piekar]

well i'm a ford tech so i can see it on ford scan tools, like the NGS, WDS, and IDS. I don't have much experience with aftermarket scan tools besides a scangauge. So i know its there, maybe aftermarket companies have not figured out the software or ford will not let that out.

I'm speaking only of fords because thats what i work on, other manufactures maybe different i'm not sure

[monroe74]

Originally Posted by piekar

i can see it on ford scan tools, like the NGS, WDS, and IDS

Thanks for the quick response.

OK, that fits what I thought (as expressed in that other thread I cited), that certain makers provide it, but they do it in a proprietary manner that's not easy to read unless you get them to tell you how to do it.

[gteclass]

I am a professional automotive tech and I have experience with several aftermarket obd2 scantools. obd2 does provide fuel pw on most models. Im not sure if the device in question uses it, but it should in order to properly calculate fuel usage. It might however just use rpm and load and mph readings to calculate a rough estimated instant fuel usage figure. The complications of using the pw to calculate the fuel usage are injector latency injector size and fuel pressure. The latency is the ammount of time it takes the injector to open and close when the signal goes to it from the ecu. The injector size is used to calculate the flow rate based on the pressure differential over the injector. The fuel pressure, while on most cars should be between 40 and 45 psi, is variable and most cars, almost all in fact do not have a fuel pressure sensor that could be logged to use it in propper calculations for fuel usage. Some cars run at higher fuel pressure, some lower, making it hard for any aftermarket device to properly work on all vehicles.

Some of the obd2 scan tool type devices i have used are...

Snap-On Solis - Awesome setup, obd0, obd1,obd2,abs,airbags,everything

AutoEnginuity Cable- Again awesome setup, primarily obd2

Tactrix Cable- Unbelievable logging capability, samples roughly 12 times per second when used on obd2 mitsubishis with the evoscan program and uses the factory communication protocols to get data that isnt even supported by obd2

CarChip- great tool for logging and testing intermittant issues

[monroe74]

Originally Posted by gteclass

I am a professional automotive tech and I have experience with several aftermarket obd2 scantools.

I think your comments are very helpful; thanks for chiming in.

obd2 does provide fuel pw on most models.

But my understanding is that this is done in a proprietary manner. Which means the data is hard or impossible to get at unless you pay a license fee to the manufacturer. Which I think is what scantool-makers generally do. But not SG.

Im not sure if the device in question uses it, but it should in order to properly calculate fuel usage.

I'm pretty sure SG does not read injector data.

The fuel pressure, while on most cars should be between 40 and 45 psi, is variable

I thought that most (all?) EFI cars have a fuel pressure regulator, to make sure that pressure across the injector is constant.

Some cars run at higher fuel pressure, some lower, making it hard for any aftermarket device to properly work on all vehicles.

But I think that for any particular vehicle, fuel pressure is a constant. Which means that it should only be necessary for the user to enter a parameter which represents the dynamic flow rate for his injectors. (The idea of dynamic flow rate, as compared with static, is that the former takes latency into account.)

That parameter could be found in various ways, including trial and error. But once it's found, it should not be necessary to worry about fuel pressure. It already takes fuel pressure into account. Assuming there is a fuel pressure regulator that holds fuel pressure constant.

uses the factory communication protocols to get data that isnt even supported by obd2

I have a feeling that when these tools show you injector data, the data is delivered via "factory communication protocols." In other words, I think the injector data is not "supported by obd2."