2nd Gen Non-Engine/Transmission Accuracy with mileage computer

[Motofreak]

After calculating my mileage with calculator and comparing with trip meter I notice that there is about a 3-4 mile disparity. In other words the trip computer says I am getting better mileage than doing the math.

 

[Gary - K7GLD]

They aren't the most accurate in the world - but DO work well for obtaining instant readouts that at least reflect the most economical speed vs load at any given point - and even tho' not

as accurate as we might like, at least once you establish the error factor, you can adjust for it in down-the-road readings...

 

[Motofreak]

So why would it be so far off? Is is the idleing? For instance I took a trip last week towing my Toy hauler, I filled up before we left, set everything, trip comp said average around 14 the entire trip when I get home and fill up again and do the math it is about 10. 5 mpg. I already compared my trip mileage to the odo and they match.

 

[Gary - K7GLD]

Must be a lousy formula in the ECM that computes fuel flow vs miles traveled...

 

[ntillm01]

I've found mine to be close to actual, plus or minus a half mpg. More off during in-town than steady driving because of the constant changes in the accelerator pedal and such.



Different-than-factory injectors, or an add-on box will affect the calculation. The engine computer knows how long it told the injection pump to squirt fuel, which is how it tells the trip computer how much fuel is being used. If another device is doing something different, more fuel is going in than the trip computer is aware of. If the length of squirt through another injector means more fuel, again, the actual fuel being used isn't seen by the trip computer. Both show better trip computer mileage than what the vehicle gets.



Also, non-factory tire size will affect the distance the trip computer thinks has been traveled. That could be it too.



Just a few thoughts...

 

[CFAR]

What comes with the Banks Stinger?

Mods that add more fueling will cause the trip comp to read high.



Mine averages 25mpgs when I'm really getting about 20. 5mpg, this is with III's and a comp.

 

[Motofreak]

My Banks comes with an Ottomind that taps into the injection pump , that could possibly have something to do with it, Not sure what size tires the computer is set for, I have 265 series. Hmm,, will do some more checking to see what is up.

Thanks everybody for the opinions, thats why I love this site.

 

[Cummins Pilot]

Mine is way off too. It drives me nuts to pay that much for a truck and it doesn't work like advertised.



We have fuel monitors in some of our aircrafts. And they are dead on. They measure how much fuel flows by the sensor in a given amount of time. Why can't Dodge set it up this way?

 

[CFAR]

I should have stated before that mine was right on before mods.

 

[ntillm01]

Originally posted by TThickstun

Mine is way off too. It drives me nuts to pay that much for a truck and it doesn't work like advertised.



We have fuel monitors in some of our aircrafts. And they are dead on. They measure how much fuel flows by the sensor in a given amount of time. Why can't Dodge set it up this way?

True fuel flow meters are too costly to put into production vehicles. Plus it's another thing to go wrong, gel up and set a P-code, etc.

I agree, though, it would be great to have a true flow sensor.

 

[Cummins Pilot]

Yeah they are spendy, especially in the aircraft world. Take the cost of something and start adding zeros behind it.



I'm still not convinced that this is a complicated problem for the engineers. Why not make it work right if your going to make it in the first place.

 

[ntillm01]

The engineers got it figured out, it's the profit-margin guys that won't let them build it

 

[dresslered]

I can live with the average mileage being off, but it sure would be nice to have an accurate 'mileage until empty' number.

 

[DHawthorne]

Mine is close sometimes and out other times. I use an excel spread sheet to keep up with it. I show the computer mileage and the real millage.



I use the hour meter, which is close, for oil change interval. I reset it when the oil is changed and try to get to it again at 150 hours.



I think the computer does not account for the fuel returned to the

tank via the return system. This would account for the higher mileage than actual readings. The system I have on my boat, which is a carburated gas engine, is right almost to the 1/10 of a gallon. There is no fuel return system there.



Dave

 

[SOOT]

mine off too

My mom's '99 runs anywhere from 3-5 mpg off. You have to do you own guessing on the "until empty calculation". Then I put some bigger tires on it, and now the odom is off too, so It's really hard to figure it out now, but with a little educated guessing and good guage monitoring, we get along fine.

 

[duaneparks]

Originally posted by dresslered

I can live with the average mileage being off, but it sure would be nice to have an accurate 'mileage until empty' number.

While my fuel mileage correction factor is about 1. 075 (because of 295/75's and the Edge Comp), the DTE figure us wayyy conservative.



However, I don't see this as a bad thing. I usually fill 'er up at 1/4 tank by the fuel gauge. That's about 400-440 miles on the highway, which is bladder busting territory anyway.



I suppose if I relied more on that overhead's info, I'd be a little more concerned about it. What bothers me more is the temp reading. Mine is off by 5-8 degrees usually. I believe it's due to my aftermarket bumper, and my lazy arse hasn't even tried to relocate the temp sensor.



Duane

 

[Doubleclutch]

Respectfully submitted for your comments

Miles divided by fuel used should be an easy thing to compute. The milage part anyway. I'm guessing that the loss of reality on the milage meter has to do with the differences in Fuel Injection pumps. The VP44 pump was a smarter pump because it had to regulate how much fuel each cylinder recieved at a given RPM, and could be relied on to give an accurate fuel flow number. The new pump just pressurizes a comon rail fuel line, and the individual injectors control the fueling. Fuel flow would be relative to rail pressure and duration of injector opening. The Mother Computer would know the RPM and how long the injector is open, but probably relies on the throttle position to determine what the rail fuel pressure should be. I'm guessing that the errors in MPG calculation result from this input.

Greg

 

[berg]

Mine allways shows less MPG than i get. about 1 to 1. 5 miles per Gal.

 

[Cummins Pilot]

My temp gauge can be off by as much as 20f. Where is the sensor anyways? I want to correct that too.