instanious and avrage MPG computer.
 

can this be done on obd0 or 1 cars? i realy want one. i've seen the JCwitny gauge but i want somthing digital. if u read here under the trip secton this is what i want. but this one is obd2.

https://www.scangauge.com

i want somthing i could splice in do a couple sensors and addon sorta like the Zemco cruse control. (if u can remimber that far back :P) anyway all i want is a little box. i can buld and put 2 7-segment displays im my cluster or to a VFD (same as LCD) display in where my clock goes. somthing simalar to like a insight cluster that give u instauous and avrage mpg.

i am proficient in electronics and programing but i dont even know where to begin on this. what sensors to use? are they readly avalible. for ex. i'd use the gas flow sensor from the zemco system but #1 it's hard to find and #2 it's not ment for the fuel injecton presures. only for carbed. maybie even go as far as somthing that will interface with the ecu. to get the sensor data that way. simaler to datalouging.

i know this is a high and drawn out request but it's somthing that've allways wanted and i'm sure that others on this site could benifit from it.

We've talked about it.
 

We've talked about it. Either you could run the ecu open loop and datalog it (honda only) or you could splice somewhere to measure injector pulse and vss and make a little chip/board to monitor and display that.

2 things...
 

On the '98 Integra (Honda OBD-II), is there a simple wiring diagram to indicate when the engine is running in open loop (like have a red LED for open-loop, green for closed). Also, is it true that Hondas/Acuras run open-loop at full-throttle, regardless of conditions?

Secondly, again on the 'teg, is there a schematic for making a fuel-economy guage? I don't need to know the numbers, just a gauge to show to the fuel consumption, low to high with hash marks in-between. I've been trying to moderately accelerate down hills, and coast up the next hill or keep the same pressure on the gas pedal. Just trying to improve the "driving efficiently" part and need some real-time info.

RH77

Quote:Secondly, again on the
 

What you want here is a vacuum mpg gauge. They suck, so just get a vacuum gauge (generally a boost gauge that measures vacuum too). More vacuum = better gas mileage ceteris paribus, so there you go, you'll have to be mindful of other factors, but it will help for compartivity.

I'll get back to you on the other ****.

EDIT: Meh.

vacuum gauge is one way to
 

vacuum gauge is one way to go for sure.

you might be able to do it digitally if you can tie a multimeter into your MAP sensor return wire, and run the multimeter wires into the cabin so you can spy on the relative voltage in different driving conditions.

you just need to know what the upper and lower limits are (which is easy to figure out in a few minutes of "extreme" driving).

(also, i understand not all cars have MAP sensors, so this might not apply to you - some use MAF instead.)

Re: vacuum gauge is one way to
 

Thanks -- I found my multi-tester in the basement today (recently moved), so I can give that a shot.

Thanks man. I had a boost guage on my Evo and it was easy enough to install. I may try that also -- fuel is saved at "negative boost" and VAC draw pressure would translate to fuel use, I assume.

RH77

Yeah, honda fuel maps are
 

Yeah, honda fuel maps are plotted in terms of vacuum/boost versus rpm. It's just a table really. So vacuum is columns and rpm is rows. You get the idea, move to less vacuum or more rpms and you're using more fuel.

Re: Yeah, honda fuel maps are
 

Thanks again. I'm glad it's pretty much that simple.

RH77

I still have all my notes
 

I still have all my notes when I was designing a driving computer to keep track of this stuff and lot's more. I just need to be inspired again to start working on it. I'm working on a microcontroller related project at work so maybe that'll spark my interest again. Just to calculate instantenous MPG wouldn't be hard at all. I might forget about reading all the sensors (like coolant temp and intake air temp) and just do MPG. I've really been thinking more and more about how nice to would be to instantly know the effect of MPG mods and driving habits in real time as I'm driving.

Flatland... you're alive...
 

Flatland... you're alive... I'm happy that you decided to visit :)

I would be more than thrilled to have a MPG readout. It's the ONE thing my car is really missing...

I think most people (at least in our little world) would love a way to measure MPG for obd1 and obd0 cars. Hell, I'd even buy one off of you. Put me down as your first customer.

Re: vacuum gauge is one way to
 

I tried this today -- but ended up with a problem. I assume I located the MAF sensor -- it was the only item on top of the intake manifold area, with a vaccum tube running to it, a tube sticking down into the manifold, and a 2-wire connector. The only other sensor nearby is what I think to be a throttle position sensor with 3 wires.

There are 2 wires: red and yellow. I hooked up the red wire and a miscellaneous ground to a multi-tester and got 14-volts, so I'm good there. I hooked the return line to the tester (yellow wire and ground) and still got 14-volts. I ran the wires into the car and drove around -- still 14-volts under all kinds of engine speeds and conditions -- warmed up and everything. I disconnected the sensor and got zero volts, but no check-engine light.

Could my MAF sensor have gone bad? I assume it's supposed to vary voltage based on the flow of air, vaccum, or something. At any rate it isn't. May need some help here.

I'm probably going to order a Vac-guage anyway, but should the MAF be reporting the same voltage all the time?

RH77

MAF should not report the
 

MAF should not report the same voltage constantly, you must've done something wrong, if you were running on a busted MAF you would be throwing code and the car would run terrible. You'd be spitting smoke you're so rich or choking the engine by running to lean, you'd definately know if the MAF was busted.

Someone on honda-tech mentioned a while back that they left their MAP sensor disconnected when they did their engine swap and as a result got 80 miles to the 12 gallon tank.

Re: MAF should not report the
 

It's very difficult to crank a car with the MAP disconnected, but it is possible.

MAP sensors should have
 

MAP sensors should have three wires (+5V, ground, and output). Often on the intake manifold is the intake air temp sensor, which is just 2 wires. If you were measuring the voltage across the 2 wires, it would make sense that it would always read 14V. No matter how its resistence changed with temp, it's the only voltage drop in that loop and will always drop whatever the supply voltage is. The MAP sensor is usually on the throttle body (which is also where the throttle position sensor is). Both are 3 wire sensors with supply, ground, and output wires. Be careful connecting power directly to these sensors. I'm 90% sure they are on 5V levels, not battery voltage.


Sorry for not posting in so long. I've been busy working a lot now that school is out (going back today though). Hopefully sitting in class I'll get bored and then start thinking about the MPG gauge and get re-inspired to do it. I don't know if I'd sell it or what, but you would need a specially programmed chip to do it, so maybe I could just sell that and some of the not so common supplies. Anyway, the project never left my mind, it just got put on hold. I ordered a PCB fab kit for my work-related microcontroller project that would be great for something like this, too. Scangauge, here I come.

Also, I've been doing the "pulse and glide" technique with my latest tank of gas. I'll respond once I fill up again.

The MAP sensor connector and
 

The MAP sensor connector and the TPS sensor connector on Honda/Acura cars look almost identical. I know on obd0 and obd1 cars (not sure about obd2, but probably the same) people often plug the TPS wire into the MAP sensor, and vice versa. In other words, they both have 3 wires.

On my intake manifold/throttle body the MAP sensor is on the front (towards the front of the car). The TPS sensor is on the back of the throttle body, near the firewall.

It sounds to me like you may be testing the wrong sensor.

There are lots of plans
 

There are lots of plans floating around for o2 sensor monitiors, but that's so simple since it's just displaying the voltage you get, but in this case you would need to make a chip for it. I wonder if I can use the chips I generally use for chipping ecus to do it.

Out of Town
 

I couldn't find it in time before the experiment, but I did some Internet research to try and find the MAF sensor. Turns out I tapped into the air-temp sensor. I may need to explore further around the throttle body when I get back (out of town). I should be reading Ohms of resistance instead of voltage, I expect.

Yeah, IAT is done in ohms.
 

Yeah, IAT is done in ohms. Good luck with it though, :p, glad that wasn't your MAF sensor.

My thoughts (shouldn't take long)
 

SVOboy has commandeered by brain on this for a minute, and ordered me to post my thoughts on it. :P Basically, we need some way of determining the amount of fuel used, and the distance travelled. These can either be directly measured, or inferred from other methods. The Honda fuel economy displays in the Insight and all that good stuff use fuel injector duration, with an assumption of a specific fuel pressure and density. These could be adjustable parameters in whatever system we devise, as they can vary from car to car, and place to place.

My thought is to use a dedicated device, like a PIC or something similar. This would allow you to sample the injector interface very rapidly using most of the processor time without hurting any other stuff, like it would on a laptop. Care must be taken to use a very high impedance input for the fuel injectors, as you don't want to interrupt their operation. Distance is as simple as speed and time from the VSS.

The average fuel economy is easy to calculate, as it is the cumulative values of fuel used and distance travelled. The "instantaneous" fuel economy would have to be the average of the last X values the device recorded. The last 10 values should provide a reasonable value, but tweaking might be required.

I'm not a programmer, so my job sort of ends here. :)

I've posted my thoughts on
 

I've posted my thoughts on using a PIC microcontroller for monitoring MPG and other variables extensively in the past. Theoretically it would be very simple to do. It's just getting up and doing it that's the hard part. I wasn't going to use any averaging in the instantaneous MPG though, just simply measure one cycle of the fuel injector, then measure one cycle of the VSS, and calculate MPG. The two would happen so fast there shouldn't be much error in the speed changing after the injectors are measured. The refresh rate would be maybe 4 to 10 times a second based off speed. A long term average might be more of a problem since the total sum would start to get very large. I think the compiler I use for PICs supports long ints, but it's something to consider. Slowing down the sample rate for the average calculation would also help.

ScangGauge lockup
 

Hey anyone ever have problems with their ScanGauge - I find mine running with the engine off since yesterday and today it locked up and would not function until I unplugged it and plugged it back in - would not operate even after I started the engine.

mine occasionally stays
 

mine occasionally stays "off" if i screw around with the ignition (on/off/on/off) too much. but i just press the "home" button and it awakens again. i haven't had to unplug it.

also, i haven't had that problem since installing my direct ignition kill switch.

i also haven't caught it "on" when it shouldn't be, though i believe i may have read of one other owner who experienced that.

on again
 

Yeah it seems to come on maybe from the remote door opener or maybe the paging alarm antenna a few inches away from the ScanGauge affecting it. The home button didn't wake it up and the LEDs were flashing on bright then glowing dimly with the display blank.