MPG reading on display correction

[MelvinPierce]

After taking my 04 quad cab, HO 2500 to FL and back, pulling a 38' toyhauler last month, my actual mpg is off 10% from what is shown on the display.



checked several times, 7-800 miles at a time, filling 3 full tanks per check.



Can the reading be corrected? By a dealer?



I can correct the reading on my CAT-C15 by myself, using the display.



Can it be done?



Thanks.



MP

 

[Prairie Dog]

Nope. I took mine to the dealer about this problem when it was new and his response was "It's just for indication". Well duh, I'd like it to indicate correctly!
So their short answer is there's no way to calibrate it.

 

[Dieselnerd]

That's pretty normal, mine is off about 10% too. Still, while towing it gives me a good indication of the kind of mileage I'm getting.

 

[Prairie Dog]

And even the 10% isn't consistent. It can be high, low or on freakishly unusual occasions, within a couple of tenths.

 

[Cosmo]

today I got 18. 0 hand calculated over 365. 5 miles (gps verified). My ODO showed 363. 2 miles, which is pretty darned close, about . 5% off, and the overhead display said I got 22. 7

22. 7 would have been nice, at $3. 799/gal.

 

[sag2]

No way to adjust. It is based on a calculation of injector pulse width and fuel pressure. If you think about it, it's remarkable it is as close as it is.

 

[p-Bar]

Buy a Scan gauge II mine is right on the money

ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool

 

[AH64ID]

And even the 10% isn't consistent. It can be high, low or on freakishly unusual occasions, within a couple of tenths.

Yep. My 2010 average was 17. 5% high, with a low of 10. 6% and a high of 25. 5%.

Buy a Scan gauge II mine is right on the money



ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool

It really depends on the year. My 05 is less accurate on the SG than the OH.



Load on a HPCR is not injector load, but CP3 load. CP3 can be at 90% but the injectors at 40% (extreme example). I can calibrate the SG and the next tank it take a 30% correction, and over and over. Even if I go 2,000 miles between calibrations it is WAY off on the next one.



Interesting it works on your 04. 5, becuase it's supposed to have the same errors as my 05, and is on the non-compatiable list from SG.

 

[MelvinPierce]

Isn't that amazing! On the Cat C-15, I can adjust the reading, using fuel correction.



For 5 years, my wife and I ran team to CA and back every week, bringing back produce. Same identical route every week. 5580 miles round trip.



Opened the Cat up to 550 hp, 1950 torque, and had to readjust the reading. After that, the reading was accurate within . 01 of a mpg, over the course of the weekly trip. Checked every week, comparing fuel with miles to the readout.



I am sure that was measuring the same.



Oh well, thanks anyway.



MP

 

[p-Bar]

Yep. My 2010 average was 17. 5% high, with a low of 10. 6% and a high of 25. 5%.



It really depends on the year. My 05 is less accurate on the SG than the OH.

Load on a HPCR is not injector load, but CP3 load. CP3 can be at 90% but the injectors at 40% (extreme example). I can calibrate the SG and the next tank it take a 30% correction, and over and over. Even if I go 2,000 miles between calibrations it is WAY off on the next one.

Interesting it works on your 04. 5, becuase it's supposed to have the same errors as my 05, and is on the non-compatiable list from SG.

Ya I may adjust maybe 1-2% between fillups. I told SG at the SEMA show a few years ago it worked great on the 04. 5

 

[retirednak]

Mine is usually way off,by as much as 3-4 mpg. With my Smarty on setting 3 and up,I see 28-29 mpg on level ground at 65 mpg. I did hear Dodge did have a reflash for the '03-'04 to correct it some.

 

[MChrist]

Melvin, what were your mpgs? I'm guessing high 6's low 7's?

 

[zzman]

Mine seems to average mpg all the time. What seems to be the WAY OFF issue is the high-end average. When coasting. the mpg goes to 99 mpg, but the low-end only goes to the real mpg at that exact time. When idling for hours, it gets 0 mpg.

Try this test: start at the top of a hill, re-set the reading and coast down the hill (a real long one if possible) then park and idle and watch the avg mpg reading. See whay ya get or not.

Ron

 

[AH64ID]

Actually when coasting on a diesel your getting much better than 99, your getting infinate. If you are truely coasting (0% throttle) and rpms are above idle there is zero fuel being injected, so your mpg is off the charts.

 

[EDankievitch]

My over haed display on my 05 was reading very high saying that I was getting 25-28 mpg for the past few years then this past summer started to read 38-47 mpg. The high readings started to show up along with a bucking while coasting down hill while in cruse. Also the engine would miss fire in fast idle. It turned out to be a cracked injector nozzle, as soon as I replaced the nozzzles everything went back to normal. The overhead display now reads 18. 3 actual is 19. 2 mpg. So... ... If your display is starting to read high it could be a sign that you've got a injector problem brewing.

 

[MelvinPierce]

Melvin, what were your mpgs? I'm guessing high 6's low 7's?

Readout was usually around 9. 8, plus or minus a few tenths.



Actual was 1 mpg less, at 8. 8.



That is towing a 38' 5th wheel, gross around 24,000, at 65-68 mpg usually, down the interstate.



How does that compare?



MP

 

[Bernie]

We called the one in my 06 the "Lie-O-Meter"
I got an 03 and it was slightly more accurate, so I was was forced to rename it the "Exaggerate-O-Meter"

 

[TFucili]

My over haed display on my 05 was reading very high saying that I was getting 25-28 mpg for the past few years then this past summer started to read 38-47 mpg. The high readings started to show up along with a bucking while coasting down hill while in cruse. Also the engine would miss fire in fast idle. It turned out to be a cracked injector nozzle, as soon as I replaced the nozzzles everything went back to normal. The overhead display now reads 18. 3 actual is 19. 2 mpg. So... ... If your display is starting to read high it could be a sign that you've got a injector problem brewing.

This is my fear. My mileage has dropped about 2-3 MPG, it smokes heavily, even though it is stock, and I can get over 1300' pre-turbo very quickly with an empty truck. I just did a couple hundred highway miles with an empty bed and it got 18. 7, while the lie-o-meter indicated 23. 9 on a fresh reset. The truck turned 50K miles on the way home. I'm not gonna be a happy camper if I've got injector issues at such low miles. I guess Bosch bought them from the guy who made the ball joints that wore out at 37K miles

 

[AH64ID]

I am not sure how much the Rokktech will drop EGT's but OEM EGT's are 1450*+.

 

[Kilroy]

Buy a Scan gauge II mine is right on the money



ScanGaugeII - Trip Computers + Digital Gauges + Scan Tool

My ScanGaugeII works really poorly in my 2004. 5. I called the ScanGuageII people said that it doesn't usually work on 04 and 05's. Sometimes reflashing will work. I haven't wanted to pay for that for "sometimes". Did yours work right out of the box?