Re: OBD-II/CAN Reader at Costco stores for $35.

SMS wrote:

> >> This one >> "
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">> >> Not the greatest reader, you have to look up the code number on-line >> after you scan at "
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"> ======== > > Not bad for $50. > However, I have always been a little leery of DIY code readers, and even > $700 ones like Snap-On and Fluke as well. > > The code reader from Toyota reads Toyota codes and interprets them. It > also is set up to work with your car. Now, most OBD systems are supposed > to use the same interface, and similar codes, but considering the ECU is a > minimum $800 box, I'm always leery of plugging something into it that may > be incompatible. > > Esp if it says "Made in China" on the package...

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Hachi (or anyone else), what do you think of the ScanGauge II (

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)? Most folks keep the ScanGauge 2 plugged into their car's OBD port 24/7 for months at a time. Problem?

I think this would be the OBD toy I'd buy if I were to buy an OBDII toy.

Reply to
Built_Well
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I have heard of them but have no experience with it.

I knew a guy that had one mounted to his dash. He liked it.

Reply to
Hachiroku

If the ScanGauge II gives actual sensor voltages and frequencies, then it is worth the money. I'm not that interested in all of the other stuff the unit displays, but it might be worth it for someone who is.

No problem leaving it plugged into the OBD II port unless you leave the vehicle parked for long periods, where it will probably drain the battery more quickly.

Reply to
Ray O

I'd like to know how they are calculating mpg just from ECU data. Makes me wonder how it can tell the mileage difference from say a

41 mpg Corolla, and a 27 mpg Chevy Impala for instance.. "actual real life ratings, I've driven both". The Impala had that mpg indicator built into the car on the headliner display. Seems to me you would have to calibrate the thing according to miles driven, and gallons of gas burned. They seem to let you input gas data.
Reply to
nm5k

The ECU now controls everything; the speedo, the odo, everything. It would be a simple calculation from the data to figure fuel economy.

Reply to
Hachiroku

In addition, the car must have some way to determine how many gallons of fuel (or more likely, how many pounds of fuel) are left in the tank. Otherwise, the car's computer would not be able to estimate how far the car can go until the tank is empty. It can use this and the miles driven to determine average mileage.

Jeff

Reply to
Jeff

Say what?

The ECU keeps a running calculation of the current consumption, then it calculates the average over time or miles. Since the ECU knows how far it has gone, and how much gas it is using and has used, then it knows the current fuel consumption rate and the average consumption rate.

Reply to
Jeff Strickland

I'd like to know how they are calculating mpg just from ECU data. Makes me wonder how it can tell the mileage difference from say a

41 mpg Corolla, and a 27 mpg Chevy Impala for instance.. "actual real life ratings, I've driven both". The Impala had that mpg indicator built into the car on the headliner display. Seems to me you would have to calibrate the thing according to miles driven, and gallons of gas burned. They seem to let you input gas data.

It's an easy matter to calculate the Injector ON time and the number of ON Cycles to arrive at how much fuel is in demand. The ECU knows how far the tires have gone, so figuring out how much gas was used to go how far is pretty easy.

Reply to
Jeff Strickland

Possibly for the factory computer. Not easily done with a scanner. Too many vehicle variables, injector flow rate, fuel system pressure, increasing on time linearly DOES NOT generate a linear fuel flow curve.

Reply to
Steve Walker

Yep, but the fuel amounts could vary to engine. And different cars have different tire sizes which could effect miles per rev. They would have to use a specially built unit for each type of car, unless the vehicles OBD-II ECU has the MPG calculating logic built into it, and calibrated for each specific engine. As far as the Impala, I don't know if the ECU provided that data, or if a 2nd unit did that using data from the ECU. I didn't check too hard, but I didn't notice different models of the Scangauge for each type of car. I think it's a one fit's all kind of deal, unless I missed something.

Reply to
nm5k

If you check out their forums all your questions are answered. You have to tell the scan tool the vehicle make and model etc.

Reply to
bad

Ya think! I guess you don't realize that EVERY make and model uses different ECU programming. While the sensors and control items (solenoids, injectors, and such) are somewhat interchangeable the ECU is not even close. Back in the 80's they used different PROM chips based on engine/trans/gearing/option packages. Now they use different flash programming in the onboard EPROM

All of the fuel data comes from the Engine Management Computer.

It is, However it only reads SOME of the OBDII data.

There are at least 10 different communications protocols in use on domestic vehicles currently. Those are ONLY the ones controlling the engines by the way, add a few more if you want to talk to the body control modules, ABS, Air Bags, Climate Controls, Entertainment systems and a few others. Now you also need the codes from every manufacturer to tell you what the data actually means. Making ONE machine that can read ALL the different data sources and communicate over ALL the protocols is darn near impossible. There are just to many. Sort of like a human trying to learn all the different languages in the world.

So they created the OBD standards. It is sort of a Morse code for cars. BUT the codes only give you the basics. Sort of like ... --- ... tells you there is a problem. It doesn't tell you WHAT the problem is.

Then they came out with the OBDII codes. Those narrow down the problems by using more codes. So now you get ... --- ... / .-- . / .... .- ...- . / .- / .... --- .-.. . / .. -. / - .... . / .... ..- .-.. .-.. Which the computer then translates to - SOS We have a hole in the hull

And it only gets worse from there. When you look at the protocols it's closer to someone talking to the Russian key operator in Chinese and the Japanese operator on the other end translating that morse code into English. You just hope the people KNOW the language and translate it properly!

Reply to
Steve W.

If I didn't realize that, I wouldn't be asking this question.. :/

I'm talking about the data they are using to calculate mpg. They are going to need more than just fuel data.

That's what I was thinking, one fits all, but according to another poster, you have to tell the scangauge what model car it is, so it does seem they have data sets for each type of car.. Or according to Bob anyway.. You would have to use different sets to be able to do that in all the various types of cars that use OBD-II. They sure all aren't equal. That would tend to tell me that the ECU does not have logic to calculate mpg on it's own, if you have to set it up for the model car you have it on.

Reply to
nm5k

1 gram of gasoline for every 14.7 grams of air, so just monitor the mass airflow sensor and do the calculation (including conversion of grams to gallons or liters). Yeah the weight of gasoline varies a little by temperature, but not enough to worry about.

That's why the devices that are able to do MPG have the caveat that the vehicle must have a mass airflow sensor for it to work.

Reply to
SMS

OK, I suppose that could work.

Reply to
nm5k

OBD-II provides the air-flow rate from the mass airflow sensor in grams per second. Since the ratio of air to fuel is precisely 14.7 to 1 for gasoline engines, you can easily calculate the amount of fuel being consumed. The fuel is precisely metered by the electronic fuel injection based on the amount of air passing through the mass airflow sensor--it's not an estimate or a rough approximation.

All you have to input for the specific vehicle is the fuel tank capacity if you want to know how many miles you can drive when the fuel tank is full. You also have to manually enter when you refill the gas tank so it knows, roughly, how much fuel is in the tank. Factory trip computers are also interfaced to the fuel tank sensor and of course they are pre-programmed with a table that has the different voltages on the fuel tank sensor versus the remaining fuel.

If the vehicle doesn't have a mass-airflow sensor then you can't calculate MPG from the data from the OBD-II interface.

Of course the other issue is whether or not you're getting proper readings of distance traveled, which is based on the speed readings from the computer, which assumes proper tire size. I don't know if when a vehicle can be equipped with different diameter tires if the manufacturer does anything to program the diameter into the computer. I.e. on my 4Runner, the very base model, which is rarely seen on the lot, has 225/75-15 (88.84" circumference) tires, but most of the vehicles sold have 265/70-16 (96.13" circumference) tires. So your actual speed could be quite a bit different than the measured speed.

Reply to
SMS

ALL of the data needed is in the ECU. Amount of fuel used gets calculated using the injector pulse timing, RPM, load percentage, throttle position, miles traveled and starting fuel load (calculated using the percentage in the tank) This get compared to a table in the ECU which it uses to determine mileage.

The reason you need to tell it the make/model is so that the machine knows which communication protocol to use. It then looks in it's memory and determines which code maps to use.

Reply to
Steve W.

The issue is that the data, in standard OBD-II format, available over the OBD-II port does not include all of these items.

However all you need to calculate fuel economy is speed and air-flow, both of which are available at the OBD-II port. The computer presumably has an accurate timer to be able to covert mph into distance traveled. Air flow linearly corresponds to fuel consumption, though if for some reason the ECU changed the mixture to be too rich or too lean then the fuel consumption would be off.

Reply to
SMS

Pulse width is there (as is fuel trim and flow rate) RPM is there Load is there TPS position is there Miles is there Amount of fuel in the tank is there

Plus a LOT of other data. Use a good scan tool and look at the live data some time. The data is there on ALL OBDII ports.

Easy enough to program a chip with the proper communications protocol and tables for fuel usage. The tables are not based on stoichiometric ratio though.

Then how do you calculate the MPG on vehicles that do not use a MAF? And there are a lot of those out there. Which DO display MPG.

Reply to
Steve W.

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