diy mpg gauge

[mpmetro]

could you take a picture of your setup and circuit, so I can then try to replicate

thaks

[txe5502]

Is there any way to use this if your computer's only audio input is mono?

[skewbe]

Are you sure it is only mono? You could only monitor fuel consumption & time OR distance & time with one channel, so it would be worth double checking with a miniscule amount of experimenting (recording) that it is indeed mono.

If I had to choose, I would choose fuel consumption, since I know how long my commute is, and I have reasonably accurate distance instrumentation in the vehicle already.

[itjstagame]

This is really awesome, finally some paved ground for a meter on my non-obd car. Can you think of a way that you'd use a serial or parralell port to capture the signals instead? Because I'd like to get more signals then just those two. Namely RPM because then I can show instantaneous HP and TQ and well and log and throw into StreetDyno.

Also one other nice thing that I'll add to this when I get it all working is an automatic crr and cid recording. I'm thinking choose a 'stop' MPH (like 20MPH entered through a text box) and then have a start button. I cruise to 70MPH, hit start and slip into neutral and let the vehicle slow to whatever the 'stop' MPH is. BAM, I know now exactly how long it takes me to slow down different thresholds, in fact instead of just 5 numbers at different speeds I have a full curve! Not exactly sure how to automate something to solve the crr cid equation based on this curve, but I'll certainly figure it out.

Do you think you could sample from the microphone jack AND line in at the same time? That might be easier than serial/parallel.

[itjstagame]

Actually thinking a bit more I'm pretty stupid to need rpm signal. I can easily get that from the injector pulses! I guess the only difference is that as their duty cycle changes the peaks may start or stop at different times causing a very miniscul shift, but the Hz*2 should be rpm.

In fact if you just had your program ask for the gearing ratios of the transmission and final drive, as well as tire diameter and size, as StreetDyno does, then you wouldn't need VSS either, since you could calculate speed based on RPM. Of course you'd contantly have to tell it which gear you were in on the fly....

[sonyhome]

Now that you mention it, you should be able to automatically find the gear ratio then with the 2 signals you get then, and when you're not in gear.

[skewbe]

sonyhome, maybe a smaller resistor on the injector would give a larger pulse signal (and thus more resolution)? I think the automatic gain control might be kicking in on the VSS and reducing both channels.

itjstagame, Yah RPM is right there, so is accelleration and deceleration, and if you know the cars weight then power can be deduced.

I don't think we care about the ratios. If you have RPM AND VSS they are the ratio when the clutch isn't slipping.

I also don't know how to get windows to let you record from more than one jack. Other ports are possible but I don't have any firm plans for them.


The coastdown tests could be completely automated, sure. The computer will gather a lot more than just 5 points on the curve, it will gather the whole curve from , say, 60mph to 0mph


One last note, trying to determine distance from rpm and gear ratios wouldn't work for me, I spend most of my time coasting with the engine off. I really need that vss signal if I want to know how far I've travelled (the 'M' in 'MPG').

[itjstagame]

Originally Posted by skewbe

One last note, trying to determine distance from rpm and gear ratios wouldn't work for me, I spend most of my time coasting with the engine off. I really need that vss signal if I want to know how far I've travelled (the 'M' in 'MPG').

Ah, very good point. Yeah, VSS is easier, I was only saying that if you only had a mono jack, just that you could get fairly close with one signal.

For calibration there are a set number of VSS pulses per mile, speed is just the rate of pulses, but I'm calibrating toward the constant number of pulses per mile?

Also how'd you decide how much fuel to attribute to each pulse? Do you have some formula based on the cc of each injector? Becaues obviously 50% pulsewidth isn't an exact amount of fuel, only if you know how much fuel the injector delivers at that 50% pulsewidth. And do most injectors ramp up linearly? ie. 80% pulsewidth used exactly 60% more fuel than 50% pulse width?

Lastly, I can solder and I can follow a diagram, but I'm afraid my electronic skills fail at the basics, so if I'm told I want to output a constant .6V I don't know if that means I need a resistor a transistor a whatever, etc. Can you give me an idea of what kind of diodes you use and what rating (varies based on VSS out signal I'm sure). And it looks like you hook the + audio signal to before the diode bridge but still on the negative (grounded) side of the VSS/injector? Or do you tap in to the + side and use the - only after the diode bridge, also aren't you making the whole ground for that injector pass through that bridge, is that an issue? Can I just use any common ground in the car? This seems it might work for the injector, but the VSS is a stand alone pulse (probably VAC)?

[itjstagame]

Actually I guess the only other signal that would be nice to have is TPS. Then you can compare throttle position to pulse widths and various loads.

I don't think I like MPG as an indicator, I'd like to see acceleration or maybe energy produced per gallon. I often wonder is accelerating slowly at 12MPG is better than accelerating quickly at 8MPG, etc. Finding the most efficient spot for acceleration coupled with EO P&G should help a lot. I would assume this would be maximum torque rpm, but I wonder how much of an effect throttle position has, especially with today's ecus, even at the max tq rpm, if you're cruising or WOT it's very different, typically different target AFRs and advances. Even building my own ECU I'm not sure 'theoretically' which would be better, lean is for efficiency but more power seems more efficient (unless it's less power/Gal).

Maybe the cruising/leaning is simply to try to help the fact engines aren't as efficient maintaining a steady state load versus accelerating against a load? That's why stuff like dropping out cylinders helps?

Sorry I keep posting, I'm just anxious to get playing with my vehicle and can't at the moment.

[caprice]

I'm lost here, but excited too... what do you have "do" to use this DIY MPG Monitor?

I know a little bit about programming, and my brother knows Java, so that helps.

In fact I have used "WIN ALDL" and an old computer to track the performance when I upgraded to TBI in my car.