| woossh |
Does anyone know if the mileage is calculated by the fuel through the intake, or tank level sensor. If the tank level sensor wouldn't't it be way high early and allow as getting toward empty?
Like the first 100 miles the needle hardly moves, but the last 100 you can almost see it move. |
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| njjoe |
woossh-
The displayed MPG is not based on an actual volume measurement, but rather a calculation based on the frequency and duration of the fuel injector pulses.
-njjoe |
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| HuskyFan |
quote:
Originally posted by njjoe
woossh-
The displayed MPG is not based on an actual volume measurement, but rather a calculation based on the frequency and duration of the fuel injector pulses.
-njjoe
Interesting! I would have thought they would use a flow meter to determine fuel rate. Where do you find this information? |
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| Kris |
| I am pretty sure Joe is right. The fuel injectors are very precise. There is no need for extra instrumentation.. |
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| njjoe |
quote:
Originally posted by HuskyFan
Interesting! I would have thought they would use a flow meter to determine fuel rate. Where do you find this information?
HF-
That is the common method used by most (all?) automakers. It gives an extremely accurate result and requires no additional hardware. The MPG info is calculated from data that is already on the engine management computer regardless of whether or not the vehicle has an MPG display.
By the way, the MPG information is updated every 30 seconds (according to the 2005 Service Manual). When reset to "*.*", the MO needs to travel 1,600 feet or 30 seconds needs to elapse before the screen will display the current value.
-njjoe |
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| biggun |
Although MPG may be calculated through the injectors, I would think that the DTE would have to consider the level of the tank to determine the amount of remaining fuel.
-biggun |
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| njjoe |
quote:
Originally posted by biggun
Although MPG may be calculated through the injectors, I would think that the DTE would have to consider the level of the tank to determine the amount of remaining fuel.
-biggun
bg-
You are 100% correct.
However, the DTE display is not very accurate. Either that, or the Nissan people have a different definition of EMPTY than I do. :D My experience has shown that I have just over 3 gallons left in the tank when the DTE reads "**". I call it the "reserve".
-njjoe |
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| Kris |
quote:
Originally posted by biggun
Although MPG may be calculated through the injectors, I would think that the DTE would have to consider the level of the tank to determine the amount of remaining fuel.
-biggun
I think that is the case. Everytime I filled the tank up the DTE was somwhere close to 330 miles. After drivinf for 100 or so miles the DTE would go up! to 350! Weird! But that how it works. Good thing is that closer to the empty the DTE are more accurate, except las 50 miles....again we need to treat it as just an indication..... |
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| njjoe |
quote:
Originally posted by Kris
Everytime I filled the tank up the DTE was somwhere close to 330 miles. After drivinf for 100 or so miles the DTE would go up! to 350! Weird!
Kris,
The DTE is based on the most recent MPG information.
If you are doing stop-and-go driving and getting around 16 mpg and then do a fill-up, the DTE is calculated against the 16 mpg. If you then hit the highway your MPG will increase into the mid to high twenties, and the DTE will increase accordingly.
-njjoe |
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| Kris |
Joe,
it wasn't the case with my car. I would drive to work and back. The MPG would be let's say 20. I would refill and the DTE would show 330 or so....I would drive in exactly the say way, the MPG would still be 20 or so, and after 100 miles or so the DTE would be 330 or something similar! There was no logic in this...but I really did not care. I always threated it as na indication only...... |
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| njjoe |
Kris,
Hmmm... interesting. My guess is that the issue is caused by the fact that automotive fuel level sensors are notorious for being inaccurate at both ends of their operating range. They are not manufactured nor calibrated to reflect the actual, absolute fuel level relative to the total capacity.
In industrial settings, "EMPTY" and "FULL" mean just that. In the automotive industry, on the other hand, when referring to fuel gauges, "empty" and "full' should be preceded by "near-".
-njjoe |
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| Kris |
In all my past cars the fuel gauges were not linear. They stayed for 100 or so miles above the “full” mark. After that they were dropping like crazy….so your observations is right.
My current car is different – the gauge IS linear! And the DTE is quite accurate. However, once the DTE drops to approximately 30 miles, suddenly I get message – low fuel on the DIC. A few miles later the NAV screen displays message: “low fuel”. Would you like to see near gas stations? (or something similar)…there is no perfect system. One needs to exercise common sense when driving a car……Oops! I forgot, common sense is really rare commodity these days….. |
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| biggun |
quote:
Originally posted by njjoe
I call it the "reserve".
-njjoe
nj,
I like that! I remember having to switch the fuel valve on my motorcycle, which was facing down, 180 degrees, to face up to get enough gas to get me to the next gas station. That was the "reserve".
On the discussion of the fuel tank sensor/gauge. I guess with the gas bouncing all around in the tank during driving, it is just too difficult or expensive to make one that is accurate. |
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| Kris |
quote:
Originally posted by biggun
......... I remember having to switch the fuel valve on my motorcycle, which was facing down, 180 degrees, to face up to get enough gas to get me to the next gas station. That was the "reserve"........................
WOW! I remember it! It was almost fool-proof!
Maybe today's automakers should adopt something similar? ;) |
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| njjoe |
quote:
Originally posted by Kris
In all my past cars the fuel gauges were not linear.
Kris,
I know what you mean. My first car, a 1970 MG Midget, had a six-gallon gas tank with (what appeared to be) a logarithmic fuel gauge. I remember I used to get 200 miles per tank. I could go about 150 miles before the needle hit the 1/2 mark. The remaining 50 miles would take the gauge from the mid-point to "E". When the needle was aligned with the "E"'s tick mark the tank was bone dry.
I had a buddy who tried to convince me the English had designed the gauge to function that way. I didn't realize until later on that the gauge, as well as the rest of the MG's systems, were simply poorly designed.:4:
The Midget was fun to drive, and fortunately for me, easy to repair.
-njjoe |
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| HuskyFan |
quote:
Originally posted by biggun
I remember having to switch the fuel valve on my motorcycle, which was facing down, 180 degrees, to face up to get enough gas to get me to the next gas station. That was the "reserve".
I once owned a 1959 VW which worked the same way. There was no fuel gauge and when the engine started missing, you would turn the fuel valve with your foot to lower the fuel pickup in the tank and then head for a gas station. |
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| njjoe |
quote:
Originally posted by HuskyFan
I once owned a 1959 VW which worked the same way. There was no fuel gauge and when the engine started missing, you would turn the fuel valve with your foot to lower the fuel pickup in the tank and then head for a gas station.
Was that the same VW that used the air pressure from the spare tire to power the windshield washer? Or was that a feature reserved for later models?
Sometimes simple is better.
-njjoe |
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| woossh |
WOW!!! Ask someone what time it is and they tell you how to build a clock.
Just kidding, great info. thanks. |
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