I recently purchased a 2006 Expy EB and love it. I have a question though. Over the last tank of gas, the computer consistently showed 18.1-18.3 mpg, however when I filled up the tank today and calculated the mileage, I calc'd only 16.3 mpg. Is this difference common?

Thanks.

 

Everyone of those computers try to make it seem like you get better mileage then you actually do. My friends Jeep did it also, as well as a few other cars. Everyone is always like "I get amazing mileage look," I tell them it is wrong and they just deny it, the computer knows more than me. Those things blow smoke everytime, never trust it

 

Thx, Brian. Are you doing the undercoating on your vehicle yourself? If so, whose product are you using? I live on a barrier island and the salt spray is pretty wicked. My Expy is from central FL and essentially rust free, but where I am now that may not last.

 

I am doing it, I am using a 3M product that seems to have lasted pretty well through the toughest winter NJ has had in a decade or so. It is just called "Rubberized Undercoating" and is made by 3M, its in a caramel and black colored spray can. If you can afford it, I would get something better though. Someone I know said Fluid Film worked well for them, I haven't used it though. I wanted to, but simply couldnt.

 

I just bought a 2000 EB expy with a 5.4L

My over head display currently says 10.4 mpg and when I bought it it said 6.something.

I know it has to be getting better than that. The truck runs to well and has been maintained very well as far as I can tell so far.

Im still on my first tank of fuel so no hard numbers yet.

Does the odometer blackout effect the calculation on the onboard system and does it register the mileage when blacked out?

My wife just told me that it blacked out while she was driving it the other day so ill check the solder connections when I get a chance.

Thanks

 

the blackout does not affect anything.

 

If you do not reset the mileage indicator everytime you fillup the vehicle, it will gradually be "off" some. This is due to changes in driving style and fuel blend changes that will yield lesser or more actual mileage per fillup that the mileage indicator is not able to account for. It's calculating mileage since it was reset last-NOT since your last filluip. On all of my vehicles that have this feature-the display is ALWAYS within .2-.5 mpg from actual.
JL

 

same here. back before the blower, it would read about 15.7 on my trips to fl. hand calculations matched. now, with the blower (when it was running on 8 cylinders!), it can read as high as 23-24, though manual math coes to about 13.5-14.25 mpg.

 

On my 2WD 2003 EB the computer has consistently overstated mileage by about 1 mpg since new. I recently went on a 200 mile trip and purposefully kept rpms below 2k, highway miles only, no a/c and the truck was unloaded. Checked actual mileage and got about 17.5 which is pretty much the best I can get. My normal hwy driving usually gets about 16.5. Computer always shows I'm getting 18 or better on the hwy.

I've always felt the high bias was on purpose (for the benefit of the car company). The computer knows how often the injectors are firing vs. wheel rotations. Assuming the tank is always filled up to the same full level (there will be variability), the computer should be able to compute a quite accurate mpg over an entire tank. Part of the problem is the float system in the tank, the computer has to adjust the mileage based upon changes in the fuel tank level. Since the float cannot accurately reflect 100% of the tank actual volume (because of the way it is designed) it seems the mileage is overstated initially when the tank to totally full and when the tank is below 1/4. Between 7/8 and 1/4 the float moves the fasted and the computer must continuously adjust. And since most of us do not run our tank to empty the mileage calculation is always biased.

In summary, the computer is adversely impacted because of the inaccuracy of the tank level readings. This is just my interpretation of the events and not based upon any specific expertise or knowledge. I'm prepared to be flamed by those in the know.

 

I don't ever reset the mpg indicator and it's pretty consistently reading high by .5 - 1 mpg.

 

That's not how the system functions. The distance to empty is the only thing that uses the current fuel level. The mileage indication uses engine RPM,load,vehicle speed,and the actual fuel injected to determine fuel mileage.
There is no reason for the manufacturers to purposely inflate the indicated mileage-there's no benefit for them at all.
JL

 

just out of curiousity, why can't the pcm calculate correct mileage in my case? it's a damn computer, how hard can it be!!

 

When the MAF or displacement of the Engine is scaled in the PCM to get load right, then you also must scale the parameters for the mileage indicator. It's very often skipped in calibrations when tunes are made.
JL

 

The benefit is in the perception of the owner, if he/she thinks they are getting better mileage than they actually are. Why would most people check their mpg if they have a computer that tells them the mpg?

Also, you're saying the computer does not adjust for changes in tank level in the calculation of mpg, it is strictly a calculation based upon the number of injector firings in relation to distance travelled? In that case it would seem the mileage would be pretty much spot on, but it's not.

 

does that mean the sct tuner man can make an adjustment to the tune to correct the readout? i am putting a used engine in this in a few weeks. once it's in, i am gonna run up to the tuner and have him make sure everything in the tune is still all set.

edit: i assume if i got something like a scangauge ii, it would be just as inaccurate as it gets it's info from the obdii port?