DIY Fuel rate meter/injector duty cycle meter/GPH

[sonyhome]

Hey,

Toss the duty cycle meter!

I found the thread about the PC-based MPG gauge. It was posted by skewbe... With Java applet and DIY injector connector.

http://www.gassavers.org/showthread....32#post6473232

http://www.gassavers.org/showthread.php?t=4250

[theholycow]

Thanks! Interesting stuff there.

The first thread is essentially the same thing that fumesucker did in this thread, which I link in the first paragraph of my original post. It's a great idea if you want to log data and review it after (and maybe graph it against OBDII data you've collected at the same time).

The second one starts that way, then turns into using a DIY duty cycle meter.

Both also talk about figuring in the VSS so you can have a MPG gauge, instead of just a fuel rate (GPH) gauge. Neither one of them provides a $33, five minute, large font display on your dashboard like hanging the dwell meter does.

I think I'll add them to the original post.

[mkiitmr2]

Could this be used as lower profile duty cycle monitor?

http://www.skycraftsurplus.com/index...OD&ProdID=1001

Very cheap, but looks like it maxes out at 50% duty cycle. But would that even be an issue? I may just pick one up and throw a ground and injector wire to it to see what I get from it. Im just looking for something lower profile that looks more integrated with my cars interior vs mounting a large DVM

[theholycow]

That's cheaper and looks smaller than the meter I used. The display is described as "5mm" (which I assume is it's height), and that's tiny for this purpose, but then it's less than half the best sale price of the Harbor Freight dwell meter. I don't know much about duty cycle meters but it looks to me like it ought to do the job.

The size of the whole unit means it won't take up the whole dash like mine does; mine hangs over most of my stereo in the truck, and in the car it covers a whole vent and part of the stereo.

I've only ever gotten to 50% under WOT near redline.

[mkiitmr2]

Originally Posted by theholycow

I've only ever gotten to 50% under WOT near redline.

Nice to know. I figured as much. My only concern is that my cars alternator keeps the car at 16.2volts while it is running which is out of the range for this duty cycle meter. Is that how much is actually going to my injectors or is the voltage going to my injectors limited so that it is kept constant?

[theholycow]

16.2 volts is awfully high. Are you running a race car DC-DC converter like in this thread?

Anyway, that's a good question. It might be difficult to measure with a volt meter because of the low duty cycle. My dwell meter reads 100% with the key turned to "On" and the engine not running; perhaps it would be possible to get a good voltage reading in that condition.

[mkiitmr2]

I have an Toyota MR2 Turbo. That is considered normal. I think 16.5volts is the highest acceptable good range for my car. So Im in the normal range. I was just looking at the wiring diagram for my car and I remembered it has an "injector resistor pack". I could measure the resistance of the pack and then calculate the voltage drop with input voltage of 16.2 to see what it puts out. But Im pretty sure that will put me at 15volts or less which is good enough for that meter based on its absolute specs. I may just try what you said also with key in on position. My injectors are grounded by the ECU and have constant power with key in on or run. Is that good? Do I tap into the power side or ground side in my case?

ERIK

[theholycow]

I'd try to add a resistor and lower the voltage going to the meter to help protect it, since the spec is 12v nominal max, 15v abs.

"constant power with key in on or run" sounds like the same behavior as my 100% duty cycle in that condition. You should be able to measure voltage like that.

You'll still tap the power side of a single injector, I'm pretty sure.

[guest001]

The fuel rate meter is really complicated and all the info seems to be spread out over multiple threads and posts which makes it even harder to replicate. Is there any definite instructions on making a mpg gauge?? I guess I need to spend way more time on here searching.........

[theholycow]

An MPG gauge is complicated and spread out over multiple threads. A simple fuel rate meter is easy and somewhat concisely laid out in 5 steps in the first post in this thread.