Scantool fun

[pasadena_commut]

My Christmas present this year was an Elm 323 based OBD2 scantool. (http://www.myscantool.com/). Today the son and I drove around trying
to figure out what the various real time readings meant. Luckily most were pretty intuitive. One wasn't though - fuel consumption.

The Protege5's OBD2 system gives only "fuel trim" readings, and these as percentages, which are sometimes negative. Does anybody know how to convert those numbers into units where "gallons" is in the numerator? (Presumably a negative fuel trim does not mean that gas is being created by the car and pumped back into the tank!) Eventually I want to be able to plot fuel usage versus other parameters (gear, speed, RPM).

I was also a bit surprised that the throttle seemed to have a hard floor of 10.5% Even coasting down from a high speed with my foot completely off the gas the throttle would not drop below that lower limit. That was also the throttle reading when the car was just idling.

 

[Nomad]

The car will not run without ingesting air to mix with the fuel.
Stuff your hand over the intake hole and I bet that percentage will drop and idle will lower.
Closed throttle still has to let air in.

 

[ProScan]

My Christmas present this year was an Elm 323 based OBD2 scantool. (http://www.myscantool.com/). Today the son and I drove around trying
to figure out what the various real time readings meant. Luckily most were pretty intuitive. One wasn't though - fuel consumption.

The Protege5's OBD2 system gives only "fuel trim" readings, and these as percentages, which are sometimes negative. Does anybody know how to convert those numbers into units where "gallons" is in the numerator? (Presumably a negative fuel trim does not mean that gas is being created by the car and pumped back into the tank!) Eventually I want to be able to plot fuel usage versus other parameters (gear, speed, RPM).

I was also a bit surprised that the throttle seemed to have a hard floor of 10.5% Even coasting down from a high speed with my foot completely off the gas the throttle would not drop below that lower limit. That was also the throttle reading when the car was just idling.

Hello,
First of all, Merry Christmas! My name is David Gore, and I developed the ProScan OBD-II scan tool that you are using. I was just taking a look at my web site's server logs and noticed some traffic from this web site and decided to take a look.

I'm glad to hear that you are having fun using ProScan! In case you haven't already done so, be sure to download version 3.0 from our web site. It was just released days ago, so you probably received version 2.0.3 with your kit. Version 3 is much better than version 2.0.3, and its free to upgrade! I also intend to add many enhancements to ProScan this year, so be sure to keep an eye on the web site.

One feature that is frequently requested is a means of monitoring fuel consumption. I am looking to implement such a feature in the near future, but the task isn't as simple as many may think.

The long term and short term fuel trims cannot be used to calculate fuel consumption. Your vehicle's computer has an internal table of values that are used to determine how much fuel should be injected based on other sensor readings. One of the most important sensors used to determine fueling is the Mass Air Flow sensor. This sensor tells the computer how much air is entering the engine. The computer looks at this value along with other sensor values such as air temperature, engine RPMs, etc and calculates the estimated fuel required (via lookup table).

Now this is where the fuel trims come into play. Your vehicle has oxygen sensors in the exhaust which roughly determine the air/fuel ratio. The O2 sensors provide feedback to the vehicle's computer and let the computer know how good of a job it is doing at maintaining a proper air/fuel ratio. If the fueling information pulled from it's internal table is resulting in a rich air/fuel ratio (too much gas), it will update the fuel trims to reduce the amount of fuel requested by the computer.

The actual amount of fuel injected is equal to the amount recommended in the computer's internal table adjusted by the short and long term fuel trims.

The long term fuel trim value is based on the average deviation from ideal air/fuel ratio over a longer time. The short term fuel trim is based on a much shorter time.

As you can now see, fuel consumption cannot be determined from the fuel trims, or any other single sensor value. In all honesty, it can't be calculated accurately using any method, unless you install a flow meter to your fuel line. However, it is possible to estimate fuel consumption using calculations based on multiple sensor readings, and I intend to implement such a feature in the near future.

Fuel injection is a rather complicated process, but I hope that this helps you better understand the process. There are many books and online articles dealing with fuel injection if you are interested in learning more.

I hope you enjoy using ProScan, and I wish you and your family a very Merry Christmas!
David Gore
Developer of ProScan
http://www.myscantool.com
Owner, Gore Research
http://www.gore-research.com

 

[Nomad]

Very cool!

 

[Maxx Mazda]

The reason why your throttle is at 10.5% is because of your IAC (idle air control) calve. the throttle is in fact fully closed, but the IAC valve runs on a bypassed pathway around the throttle butterfly and is a solenoid electronically controlled by the ECU to either open or close to allow the proper amount of air to enter the engine, mainting the specified idle. This is how your car achieves a higher idle while the A/C is on and when the car is cold. The Scan tool intercepts the signal from the ECU, which, more specifically is the TPS (throttle position sensor) signal, which itself encompasses the IAC reading. Hope that wasn't too confusing.

 

[Maxx Mazda]

Btw, I want one of these scan tools now. Pretty cheap too. You ship to Canada?

 

[Maxx Mazda]

Just out of curiosity, which kit did you order? The Ford one, or the import one, or what?

 

[pasadena_commut]

Just out of curiosity, which kit did you order? The Ford one, or the import one, or what?

I bought the ISO one.

There is a new reader coming out in January which does all protocols, albeit for $50 more. It's a pretty safe bet that the multiprotocol OBD2 reader is based based on the new Elm327 chip.

 

[pasadena_commut]

The reason why your throttle is at 10.5% is because of your IAC (idle air control) calve. the throttle is in fact fully closed, but the IAC valve runs on a bypassed pathway around the throttle butterfly and is a solenoid electronically controlled by the ECU to either open or close to allow the proper amount of air to enter the engine, mainting the specified idle. This is how your car achieves a higher idle while the A/C is on and when the car is cold. The Scan tool intercepts the signal from the ECU, which, more specifically is the TPS (throttle position sensor) signal, which itself encompasses the IAC reading. Hope that wasn't too confusing.

Uh, maybe I'll understand that after reading it another dozen times. My principal confusion arises from the automatic transmission shift pattern graphs on page 15 of http://protege5.ugly.net/05-17.PDF . These graphs seem to indicate that throttle values smaller than 10.5% should be possible. How does one reconcile those graphs with the explanation quoted above?

This was also very useful:

The long term and short term fuel trims cannot be used to calculate fuel consumption. Your vehicle's computer has an internal table of values that are used to determine how much fuel should be injected based on other sensor readings. One of the most important sensors used to determine fueling is the Mass Air Flow sensor. This sensor tells the computer how much air is entering the engine. The computer looks at this value along with other sensor values such as air temperature, engine RPMs, etc and calculates the estimated fuel required (via lookup table).

If I'm interpreting this correctly we can't really know more than the onboard computer does. If we knew all of the relevant sensor values, and the values in the lookup table, then we would know how much fuel the computer was trying to put into the engine. If something was out of whack so that it wasn't actually achieving that, our calculation would be wrong. But then, so would be the computer's, so neither it nor we would really know how much fuel was going in. Is that right?

That brings up the obvious next questions:

1. Exactly which sensor values does the computer reference?
2. What are the values in the lookup table? (Or if it's more complex than
that, what is the formula the computer uses).

Perhaps one of our Mazda technician friends can answer these for us?

 

[ke20sprinter]

hmmm...The newer version supports CAN systems...Something I wanted for my wifes Nissan Murano (I installed the OEM navi system on it, but can't get the CAN info working since then). Not bad for $150. I've seen some for way more than that!

Thanks

WiL

 

[ProScan]

Btw, I want one of these scan tools now. Pretty cheap too. You ship to Canada?

Yes, we ship worldwide. We use Express Mail to avoid customs delays, and you will have tracking information as well. Shipping to Canada is $20 USD in addition to purchase price.

Most Mazda's use ISO protocol, but I'd say the new ones are switching to CAN. If you'll only use the scan tool on your vehicle, then you can save a few bucks and get the ISO. However, our new ElmScan 5 kits support ALL protocols (VPW, PWM, ISO, and CAN) and in a smaller, more convenient interface. They will begin shipping in the second week of January. If you pre-order now, you'll save $10.

Also, version 3.0 is now available and has several new features such as recording and playback of sensor data, etc. I haven't had time to update the website with new screenshots and details.

I'll try to keep an eye on this thread and answer questions, but my wife is 9 months pregnant and will probably deliver this week, so I may not be able to respond again for a week or so.

Thanks,
David Gore
Developer of ProScan
http://www.myscantool.com

 

[BlkZoomZoom]

Hello,
First of all, Merry Christmas! My name is David Gore, and I developed the ProScan OBD-II scan tool that you are using. I was just taking a look at my web site's server logs and noticed some traffic from this web site and decided to take a look.

I'm glad to hear that you are having fun using ProScan! In case you haven't already done so, be sure to download version 3.0 from our web site. It was just released days ago, so you probably received version 2.0.3 with your kit. Version 3 is much better than version 2.0.3, and its free to upgrade! I also intend to add many enhancements to ProScan this year, so be sure to keep an eye on the web site.

One feature that is frequently requested is a means of monitoring fuel consumption. I am looking to implement such a feature in the near future, but the task isn't as simple as many may think.

The long term and short term fuel trims cannot be used to calculate fuel consumption. Your vehicle's computer has an internal table of values that are used to determine how much fuel should be injected based on other sensor readings. One of the most important sensors used to determine fueling is the Mass Air Flow sensor. This sensor tells the computer how much air is entering the engine. The computer looks at this value along with other sensor values such as air temperature, engine RPMs, etc and calculates the estimated fuel required (via lookup table).

Now this is where the fuel trims come into play. Your vehicle has oxygen sensors in the exhaust which roughly determine the air/fuel ratio. The O2 sensors provide feedback to the vehicle's computer and let the computer know how good of a job it is doing at maintaining a proper air/fuel ratio. If the fueling information pulled from it's internal table is resulting in a rich air/fuel ratio (too much gas), it will update the fuel trims to reduce the amount of fuel requested by the computer.

The actual amount of fuel injected is equal to the amount recommended in the computer's internal table adjusted by the short and long term fuel trims.

The long term fuel trim value is based on the average deviation from ideal air/fuel ratio over a longer time. The short term fuel trim is based on a much shorter time.

As you can now see, fuel consumption cannot be determined from the fuel trims, or any other single sensor value. In all honesty, it can't be calculated accurately using any method, unless you install a flow meter to your fuel line. However, it is possible to estimate fuel consumption using calculations based on multiple sensor readings, and I intend to implement such a feature in the near future.

Fuel injection is a rather complicated process, but I hope that this helps you better understand the process. There are many books and online articles dealing with fuel injection if you are interested in learning more.

I hope you enjoy using ProScan, and I wish you and your family a very Merry Christmas!
David Gore
Developer of ProScan
http://www.myscantool.com
Owner, Gore Research
http://www.gore-research.com

Very nice information. Kinda disappointed you didn't get into the additive and multiplicative explinations of the fuel trims though, thats where the fun begins.

 

[Maxx Mazda]

Uh, maybe I'll understand that after reading it another dozen times. My principal confusion arises from the automatic transmission shift pattern graphs on page 15 of http://protege5.ugly.net/05-17.PDF . These graphs seem to indicate that throttle values smaller than 10.5% should be possible. How does one reconcile those graphs with the explanation quoted above?

Simply put, all that grap shows you is when the transmission is told by the PCM to shift. If you look, the car is able to upshift with a TPS value of 10.5 and below. If yo're coasting, the throttle (including the IAC valve) can be less than 10.5% open, because the engine is in a sense being driven by the wheels. Hope that makes sense.

 

[Robot Romeo]

this thing is cheaper than the "gtech" and has more uses. very cool. (thumb)

 

[ProScan]

this thing is cheaper than the "gtech" and has more uses. very cool. (thumb)

(Sorry for the delay in responding, but my wife delivered our first child last week! As a side-note, I requested sponsorship info from Antoine and I will more than likely become a sponsor of this forum.)

I bought a G-Tech competition for $350 a couple years ago, and I NEVER got reliable results. I spent an entire night on the road, recalibrating, doing 1/4 mile pulls, over and over again, and kept getting crazy results. That is actually what prompted me to implement the dyno and track performance tools in ProScan. The track performance tool in ProScan is dead on accurate as long as you don't get heavy wheelspin. Estimating hp and tq from acceleration data is much more difficult due to the # of variables involved, but in my opinion ProScan does a much better job than the G-Tech. ProScan can accurately read vehicle speed and RPMs, it doesn't "sense" RPMs through the cigarette lighter voltage. Also, ProScan doesn't depend on the accelerometers being perfectly level throughout the course of the run.

The only reliable way to measure hp and tq is on a chassis dyno. However, ProScan does a much better job than all other acceleration-based estimators, and with no calibration headaches... just plug up and go! Oh, and don't forget that ProScan is the cheapest OBD-II analysis tool available.

I look forward to sponsoring this forum and providing you guys with great service and support and great discounts.

Thanks!
David Gore

 

[Maxx Mazda]

Are you shipping the all in one kits yet?

 

[viVid]

Just put this on my "buy" list...

 

[viVid]

Oh, and I assume these vehicles all use the ISO protocol?

2001 Volvo V70 T5
2000 Toyota Celica GTS
1995 Toyota MR2

Thanks!

 

[Moeed]

The vovlo might be pwm.

 

[i12drivemyMP5]

Cool stuff, I've been using auto-tap scantool since 1999 or so with the mustang I had. It has all the ford specific codes but does generic set for other obd-II cars. I've used it on lots of different friends' cars. It has the same sensor readings & can be text chart or changed to dash board looking gauges in sweep or digital. It also has the recording feature but has no dyno type features. I use it USB'd to an older laptop that is designated primarily for scantool use. The dyno & future fuel usage info would be cool extra features.