DIY Fuel rate meter/injector duty cycle meter/GPH - Page 4 - Fuelly Forums

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Old 07-11-2009, 11:18 AM   #31
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Originally Posted by theholycow View Post
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.
ok, but I don't really see this being that useful. if the car has a tach. you could us a vacuum gauge instead. I don't think attempting to drive with the lowest possible duty cycle get the best mileage.
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Old 07-11-2009, 11:30 AM   #32
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Using a tach and a vacuum gauge is a roundabout way to guess how much fuel you're using; using the meter tells you exactly how your fuel injectors are operating. It is most useful in two ways:
1. Choosing a gear to use at a given speed/grade
2. Detecting DFCO

It is nowhere near as useful as a MPG gauge, and if it wasn't far cheaper and easier than one then it wouldn't be worth doing.

One advantage is does over OBDII equipment is that it's realtime. OBDII equipment refreshes every second or every two seconds or whatever your car supports.
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Old 07-11-2009, 12:25 PM   #33
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Originally Posted by theholycow View Post
Using a tach and a vacuum gauge is a roundabout way to guess how much fuel you're using; using the meter tells you exactly how your fuel injectors are operating. It is most useful in two ways:
1. Choosing a gear to use at a given speed/grade
2. Detecting DFCO

It is nowhere near as useful as a MPG gauge, and if it wasn't far cheaper and easier than one then it wouldn't be worth doing.

One advantage is does over OBDII equipment is that it's realtime. OBDII equipment refreshes every second or every two seconds or whatever your car supports.
looking at a basemap/startup map for a Honda. the pulse width obvioulsy goes down with vacuum, but not so linear with rpm. so you could see at what rpm your using the lease amount of fuel. the only thing that can effect rpm without changing TP is what gear your in........ I lost my train of thought here. this is kinda complicated. I have a WBO2 :-) so I know when I'm in fuel cut off. but even if you didn't have any gauge if you knew under what specific operation it was occuring. it's published for hondas that if the tps % is 0 and its above like 1000's the injectors aren't squirting fuel. you don't need a gauge to tell you that.

Explain #1, choosing a gear.

Your right, obd2 is sampling the data. though with some of the better scan tools it almost seem as if it isn't. I was pretty hesitant about believing scan tools after reading about this. but after using them, and testing the values at the sensors vs whats on the scan tool. I trust them more. I'm more of an older school type of person that like osciliscopes and testing at the sensors/connectors. it's so funny when people don't know how to test pre obd2 sensor, etc. without a scan tool
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Old 07-11-2009, 12:34 PM   #34
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Choosing a gear: Let's say you're going 30mph up a hill, and you're not sure if you'll use more gas in 3rd or 4th. In 4th you have to lay on the throttle pretty hard but in 3rd your RPM gets pretty high. With the meter, you'll try it both ways and whichever gear shows lower on the meter is the more efficient gear.

Since you have all that data on your Honda, you could do the math ahead of time and memorize the tables; but most people don't have that data and wouldn't want to memorize the table.
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Old 09-19-2010, 09:28 PM   #35
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Re: DIY Fuel rate meter/injector duty cycle meter/GPH

These are really good! Keep it up!
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