Wild MPG instant reading - Page 3 - Ram 1500 Diesel Forum
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post #21 of 40 Old 11-30-2014, 08:45 PM
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I really doubt this truck has a barometric pressure sensor on it. The truck does of course adjust for changes in O2 density (lower ambient pressure). But the sensor for adjusting for O2 fluctuations is the O2 sensor, not a barometric sensor.
Manifold Absolute Pressure.....MAP
Which is a fancy way of say air pressure or lack thereof.

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post #22 of 40 Old 11-30-2014, 09:37 PM
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Am I missing something? Why can't the ECM know fuel flow by counting the number of times the injectors fire? I would think the flow would be easier to control digitally by injecting the same amount of fuel each time and modulating the firing rate. The distance traveled is known. Divide the two to get mpg. Who cares about temperatures, pressures, etc? MPG is about what has already happened, not predicting the future. What I am reading here sounds like an awfully complicated way to do this.
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post #23 of 40 Old 11-30-2014, 09:49 PM
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Originally Posted by rdefayette View Post
Manifold Absolute Pressure.....MAP
Which is a fancy way of say air pressure or lack thereof.


MAP is NOT the same as ambient pressure. The air filter, inter-cooler, turbo all contribute to pressure differences between ambient and manifold pressure. But more importantly the MAP sensor is there for boost calculations, not MPG.
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post #24 of 40 Old 11-30-2014, 11:03 PM
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Am I missing something? Why can't the ECM know fuel flow by counting the number of times the injectors fire? I would think the flow would be easier to control digitally by injecting the same amount of fuel each time and modulating the firing rate. The distance traveled is known. Divide the two to get mpg. Who cares about temperatures, pressures, etc? MPG is about what has already happened, not predicting the future. What I am reading here sounds like an awfully complicated way to do this.
It is a complicated way to do this. I didn't write the algorithm taking into account all the parameters/variables that the designers did include. I guess if it was easy the MPG display would be dead nuts on like the odometer is when measuring distance (well almost this accurate AND consistent too). The odometer doesn't give wildly variable numbers when we take our foot off the throttle or accelerate does it. Problem is all the variables (as I stated before) in the program. IF there was a way to accurately WEIGH the fuel in the tank then it would be REAL easy get an accurate/consistent MPG number. distance traveled / lbs/hr fuel burned. That would be THE way to go.

Bob
Current; '04.5, 2500HO,Auto,QCLB,4x4,CAI,4" TB,Smarty Jr,AD II 100,Flex-A-Lite fans, homebrew headache rack, "wedge" cap, rear bumper'03, 3500,QCLB,4x4,Dually,RIP
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post #25 of 40 Old 11-30-2014, 11:24 PM
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Originally Posted by ED_Lover View Post
MAP is NOT the same as ambient pressure. The air filter, inter-cooler, turbo all contribute to pressure differences between ambient and manifold pressure. But more importantly the MAP sensor is there for boost calculations, not MPG.
Ok, guess I should be a clearer. MAP is the absolute pressure difference between ambient pressure (atmosphere) and manifold (intake) pressure. The MAP sensor is required to determine the pressure differential between the manifold pressure and atmospheric pressure. It can also be used to calculate airflow.
here to save a lot of typing. getting lazy.
MAP sensor - Wikipedia, the free encyclopedia

Bob
Current; '04.5, 2500HO,Auto,QCLB,4x4,CAI,4" TB,Smarty Jr,AD II 100,Flex-A-Lite fans, homebrew headache rack, "wedge" cap, rear bumper'03, 3500,QCLB,4x4,Dually,RIP
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post #26 of 40 Old 11-30-2014, 11:41 PM
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Ok, guess I should be a clearer. MAP is the absolute pressure difference between ambient pressure (atmosphere) and manifold (intake) pressure. The MAP sensor is required to determine the pressure differential between the manifold pressure and atmospheric pressure. It can also be used to calculate airflow.
here to save a lot of typing. getting lazy.
MAP sensor - Wikipedia, the free encyclopedia
Wouldn't an even more accurate measurement be a flow meter on the fuel line?


I still don't see why the designers would include any temps, boost, etc. into the MPG calculation when the injection duty cycle would be a much closer measurement of fuel consumption.


The variation between the truck MPG and real-world is likely due to variations in the amount of energy contained in the fuel. It could also be that assuming each injector delivers the same amount of fuel every time is inaccurate (rail pressure varies?).
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post #27 of 40 Old 11-30-2014, 11:53 PM
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Wouldn't an even more accurate measurement be a flow meter on the fuel line?


I still don't see why the designers would include any temps, boost, etc. into the MPG calculation when the injection duty cycle would be a much closer measurement of fuel consumption.


The variation between the truck MPG and real-world is likely due to variations in the amount of energy contained in the fuel. It could also be that assuming each injector delivers the same amount of fuel every time is inaccurate (rail pressure varies?).
That's why I said fuel weight in the tank. Flow meters would be nice BUT there is also the fuel return line to deal with. Not all the fuel that goes through the pump is injected into the engine. More is returned to the tank than is actually used. With the V6 Motori Common Rail engine there would have to be 6 (or however many cylinders there are on any given Common Rail engine) flow meters (1 for each cylinder) as all fuel leaving the high pressure pump is under high pressure to the fuel "log" then to the individual injector lines. The fuel that is not used (metered) through the injectors is "dumped/returned" from the fuel "log" back to the tank.

Bob
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post #28 of 40 Old 12-01-2014, 12:19 AM
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That's why I said fuel weight in the tank. Flow meters would be nice BUT there is also the fuel return line to deal with. Not all the fuel that goes through the pump is injected into the engine. More is returned to the tank than is actually used. With the V6 Motori Common Rail engine there would have to be 6 (or however many cylinders there are on any given Common Rail engine) flow meters (1 for each cylinder) as all fuel leaving the high pressure pump is under high pressure to the fuel "log" then to the individual injector lines. The fuel that is not used (metered) through the injectors is "dumped/returned" from the fuel "log" back to the tank.
Why would you need 6? Two would be sufficient I would think (a supply and a return).
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post #29 of 40 Old 12-01-2014, 11:05 AM
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Why would you need 6? Two would be sufficient I would think (a supply and a return).
2 would work you are correct. I was just thinking for accurate data acquisition (fuel flow) for each cylinder. Getting a little to in depth. we use individual pyro's for each cylinder when testing. I was going a little overboard I guess. Old habits....as many channels of data as possible. removes more variables

Bob
Current; '04.5, 2500HO,Auto,QCLB,4x4,CAI,4" TB,Smarty Jr,AD II 100,Flex-A-Lite fans, homebrew headache rack, "wedge" cap, rear bumper'03, 3500,QCLB,4x4,Dually,RIP
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post #30 of 40 Old 12-01-2014, 11:30 AM
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2 would work you are correct. I was just thinking for accurate data acquisition (fuel flow) for each cylinder. Getting a little to in depth. we use individual pyro's for each cylinder when testing. I was going a little overboard I guess. Old habits....as many channels of data as possible. removes more variables

So do you work for one of the Big 3?
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