Update on Odo and Speedo errors

litton · **Posted:** Sat Sep 02, 2006 6:34 pm

When we retruned to Tucson last week, I measured the distance on the trip ODO, the speedo ODO, and my GPS. In addition I check the speed agains the GPS also.

The GPS is a Magellan Explorist XL tracking at least 9 satallites. This trip goes though mountains outside of S.D. and then all desert the rest of the way. The GPS was wedged between the instrument cluster dome and windshield so it had great satalite visibilty. The trip was reset in Gila Bend when I got fuel. Varience was computed on four legs....SD to Yuma, Yuma to Gila Bend, Gila Bend to home and SD to home. In all instances the trip and odo agreed 100% and the varience was steady at 6% low (from actual).

Of interest is that the speedo is exactly 3 mph low (from actaul) at any speed. This is not a % but a linear error....possibly in the Zero adjust.

On a side note, I got 25 mpg at 65 - 70, 21 mpg at 75, and 20 mpg at 85 ( all indicated) If I correct for odo error the mileage goes up 6% The EVIC fuel ecomony ranged from dead on to 2.5% high (using uncorrected mileage).

Loc Odo Trip Gps Var.

SD 743 5.7 0
Yuma 911 174.2 177.4

SUB 168 168.5 177.4 -0.05

Gila Bend 1023 285.9 295.5
112 111.7 118.1 -0.06

Home 1170 147 450.9
SUB: 147 147 155.4 -0.06

Total 427 427.2 450.9 -0.06

I think this cofirms what other have seen as well. I will bring all this info, and more, to the dealer when I take it in for service......should be an interesting discussion.

BLake · **Posted:** Sat Sep 02, 2006 8:27 pm

That is exactly what I am seeing. Speedometer 3MPH off at all speeds. Trip odo off by 5-6%. I haven't checked the regular odometer yet.

I need to take my Jeep in for a few things. I'm getting 16-22 miles per gallon and that ain't right. Maybe some setting in the computer isn't correct, as in, it is set up for as a Limited with different wheel size vs. a Sport.

gsbrockman · **Posted:** Sun Sep 03, 2006 7:50 am

BLake wrote:

I'm getting 16-22 miles per gallon and that ain't right.

What are your results hand-calculated, with at least two consistent fill-ups back to back ?

Greg

Joe Romas · **Posted:** Sun Sep 03, 2006 3:04 pm

BLake wrote:

That is exactly what I am seeing. Speedometer 3MPH off at all speeds. Trip odo off by 5-6%. I haven't checked the regular odometer yet.

I need to take my Jeep in for a few things. I'm getting 16-22 miles per gallon and that ain't right. Maybe some setting in the computer isn't correct, as in, it is set up for as a Limited with different wheel size vs. a Sport.

Blake.

Is yours a 06 :?:

I have a "Jeep Liberty 2006" brochure and it shows the CRD Sport and Limited both as having the 16" Mechanica Cast Aluminum wheels. My tires are P225/75R16 OWL ALL Season. the wheel rims are 16" x 7".

BLake · **Posted:** Sun Sep 03, 2006 6:54 pm

Yes mine is an 06 with whatever is standard on the Sport CRD. There are 17" wheels optional on the Limited I think.

My mileage has been trending down. One tank was 16.5 the next was 20, 22 before that. Factoring in a gallon extra that I can sometimes get in if the fuel isn't foaming changes the MPG by +- 1MPG. 6% odometer error changes the MPG by the same amount. I keep a spread sheet with all of the data and I don't have an EVIC. I even have columns for corrections that I think are possible.

Joe Romas · **Posted:** Sun Sep 03, 2006 7:43 pm

BLake wrote:

Yes mine is an 06 with whatever is standard on the Sport CRD. There are 17" wheels optional on the Limited I think.

My mileage has been trending down. One tank was 16.5 the next was 20, 22 before that. Factoring in a gallon extra that I can sometimes get in if the fuel isn't foaming changes the MPG by +- 1MPG. 6% odometer error changes the MPG by the same amount. I keep a spread sheet with all of the data and I don't have an EVIC. I even have columns for corrections that I think are possible.

I was told and the brochure indicated, the 16" wheels I mentioned were the only ones that came on the CRD, (at least for the 06 my) maybe beause a weight factor for the CRD engine :?:

Yes Limiteds come standard with 17" wheels EXCEPT the CRD. I guess a dealer could switch with another to make a sale though. If your fuel is foaming that's a sign of a low class fuel. Better fuel is treated with something that stops the foam. Only problem is it's REAL easy to run it out on the ground :roll:

Low grade fuel could be your mileage problem. Most cars speedometers read high on purpose because some arm of the government says no cars will read less then actual. VW jettas are around 6% high on the speedometer but the odometer is dead on. I've not driven my crd enough to determine if it's off. My fuel mileage is just above 20 mpg with all city driving and short trips. That's almost twice my 99 Cherokee

jeep06 · **Posted:** Sun Sep 03, 2006 8:47 pm

I finally got out my Lowrance global map 100 today and checked out my speedometer, it is also off about the same as everyone else is reporting. Had cruise set at 60, GPS read 57.4-57.6 mph. But on a good note, when I uprade my tires hopefully to the next size bigger, it should make the speedo about dead on.

BlackLibertyCRD · **Posted:** Sun Sep 03, 2006 11:01 pm

jeep06 wrote:

I finally got out my Lowrance global map 100 today and checked out my speedometer, it is also off about the same as everyone else is reporting. Had cruise set at 60, GPS read 57.4-57.6 mph. But on a good note, when I uprade my tires hopefully to the next size bigger, it should make the speedo about dead on.

Nope, bigger tires will make it worse, smaller tires will make the wheels, gears, trans output shaft spin faster, resulting in higher reading for the output speed sensor.

jeep06 · **Posted:** Tue Sep 05, 2006 3:26 pm

Tire size has nothing to do with the reported speed or miles traveled on the odometer of the Jeep. The only way tire size would influence the speedometer/odometer is if they were driven by an independent device that measured actual ground speed (AKA a ground driven 5th. tire and speed sensor).

Jeger · **Posted:** Tue Sep 05, 2006 3:34 pm

jeep06 wrote:

Tire size has nothing to do with the reported speed or miles traveled on the odometer. The only way tire size would influence the speedometer/odometer is if they were driven by an independent device that measured actual ground speed (AKA a ground driven 5th. tire and speed sensor).

You are talking about the odometer on you gps right?

jeep06 · **Posted:** Tue Sep 05, 2006 3:49 pm

You are talking about the odometer on you gps right?[/quote]

No the speedo/odometer on the Jeep. The speedometer on the Jeep would report you were going 60 mph regardless of what tire size you have, but your actual speed reported on a GPS or independent measuring device will show you the actual ground speed.

jeep06 · **Posted:** Tue Sep 05, 2006 4:03 pm

jeep06 wrote:

You are talking about the odometer on you gps right?

No the speedo/odometer on the Jeep. The speedometer on the Jeep would report you were going 60 mph regardless of what tire size you have, but your actual speed reported on a GPS or independent measuring device will show you the actual ground speed.

Here is a link to show how much the tire dia. will change "actual" ground speed, not what is reported by the vehicle speedo/odometer........ http://www.csgnetwork.com/multirpmtirecalc.html

Jeger · **Posted:** Tue Sep 05, 2006 4:08 pm

Ok i see what you are saying now, I think BlackLibertyCRD was referring to the difference made to "actual" speed by changing tire sizes. It makes sense now, its just that the wording was about as clear as mud before.

jeep06 · **Posted:** Tue Sep 05, 2006 4:30 pm

Jeger wrote:

Ok i see what you are saying now, I think BlackLibertyCRD was referring to the difference made to "actual" speed by changing tire sizes. It makes sense now, its just that the wording was about as clear as mud before.

Sorry about the mud, must be too much barley pop or the lack of??? :oops:

Update on Odo and Speedo errors

Who is online