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  #25  
Old 12-11-2009, 12:25 AM
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Re: Accuracy of on board trip computor

Yeah, the one thats like **** mpgs, some russian pic..........
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  #26  
Old 12-11-2009, 02:14 AM
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Re: Accuracy of on board trip computor

i think there is something wrong with mine too lol it says i get 27mpg driving the NE extension of the PA turnpike at 70mph the whole way roundtrip which is a tank of gas. once i do the actual math its around 20mpg
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  #27  
Old 12-14-2009, 02:17 PM
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Re: Accuracy of on board trip computor

Filled up today and checked and re-checked all figures

OBC is showing 31.2 US MPG

My "real" calculations give an improved (over last time) 28.12 UK MPG

Now that works out at 23.41 US MPG

So I am still way off and the OBC is still giving alarming readings that no way reflect what is actually being used

Any idea's of where I should be looking to correct this?

PS todays OBC reading is 33 US MPG, which is 39.63 UK MPG, a figure that I will concede, is unlikely to be achievable from a vehicle of this size and weight
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  #28  
Old 12-14-2009, 03:35 PM
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Re: Accuracy of on board trip computor

Wow that is way off (24%+) so I think there is def something wrong. Have you determined your odometer is reading mileage accurately (ie if you make a 300 mile trip based on mapquest or road signage does it give you the same mileage on your odometer)? Have you changed your tire size at all? I apologize if this is known info already...just can't figure out why it would be that off unless the calibration is off...
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  #29  
Old 12-14-2009, 03:44 PM
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Re: Accuracy of on board trip computor

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Originally Posted by 08Hemi View Post
Wow that is way off (24%+) so I think there is def something wrong. Have you determined your odometer is reading mileage accurately (ie if you make a 300 mile trip based on mapquest or road signage does it give you the same mileage on your odometer)? Have you changed your tire size at all? I apologize if this is known info already...just can't figure out why it would be that off unless the calibration is off...
The odo mileage is within 1% of the GPS tracking device fitted to my car

Todays odo is 357 miles ,and the tracking shows 360.3 which is the 1%

The tracking is spot on real time stuff

The tyre size is the standard Goodyear Wrangler HP A/W 245/65 R17"

357 is an average days driving, so you can understand why I am so interested in sorting this
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Old 12-14-2009, 05:48 PM
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Re: Accuracy of on board trip computor

even if you didnt drive that much it is still an issue being that far off! well since my first idea was nixed, when was the last time you reset your neg terminal? other than that, I don't think I can be of much asssitance. have you taken it to the dealer?
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  #31  
Old 12-14-2009, 06:09 PM
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Re: Accuracy of on board trip computor

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Originally Posted by 08Hemi View Post
even if you didnt drive that much it is still an issue being that far off! well since my first idea was nixed, when was the last time you reset your neg terminal? other than that, I don't think I can be of much asssitance. have you taken it to the dealer?
No, we have few solus Jeep dealers in the UK, most are actually Mercedes Benz dealer/workshops, so you can guess at the labour rate (its £95.00 per hour at my local dealer in Witham)

I may take it to a local shop and start by having the fuel filter changed, then the air filter (can I get a K&N for the CRD?) and just work through the obvious

Being over 3 years old its out of Jeep warranty, and while the car is covered with a warranty its more of a breakdown and parts thing than a fault sorting thing

What do you mean by "restting the neg terminal"

What I don't get is why it drives and performs so well and returns such poor MPG

Was there ever issue's with the EGR system on the CRD?
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  #32  
Old 12-14-2009, 06:11 PM
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Re: Accuracy of on board trip computor

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oh yeah...mine is a 2wd Ryan!!! I think that is where we differ the most, right?
oh yeah.. that and my black paint looks way better than your white
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  #33  
Old 12-14-2009, 06:26 PM
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Re: Accuracy of on board trip computor

HAHA and it is a year older with a lot more miles!

All that means is removing the negative terminal from your battery. This resets the interior electronics and could (maybe and its a big maybe) reset your trip computer and get it closer to accurate. Remove the (-) terminal for about 20-30 mins and then put it back on your. you may lose your am/fm presets but it is worth a shot!
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  #34  
Old 12-14-2009, 06:28 PM
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Re: Accuracy of on board trip computor

TONS more miles, I'm sure of it!
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  #35  
Old 12-15-2009, 12:58 AM
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Re: Accuracy of on board trip computor

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I will concede, I am going to check this over the next few tankfulls!!

I am certain the figures I am working with are correct, I did 327.5 miles according to the trip, I filled up and it took 53.55Litres which is 11.77 UK gallons, simple calculation of 11.77 divided by 327.5 = 27.82 (UK) mpg or 23.16 (US) mpg

This is the 3L CRD driven 90% on motorway (highway) at between 60- 80 mph traffic allowing with no serious use of acceleration and very little town work

It is also "chipped" which on the previous CRD lifted mpg by 10% and on this one the OBD shows a 5% improvement

The tyres are run at 38PSi as opposed to the factory setting of 33, no roof rails, AC is always on, I don't sit with the engine idling I always switch it off

Im not farmiliar with Jeeps diesel, but im very familiar with the preformance diesel industry (mostly cummins and duramax motors)

With my 03 cummins powered dodge, any sort of programing would greatly change what the computer calculated. With the dodge and chevys throttle response is changed. Meaning that a half inch of throttle with programing could equal 1 inch of thottle with stock programing. The computer calculates mpg directly from throttle position, vehicle speed and load.

My two cents
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  #36  
Old 12-15-2009, 08:50 AM
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Re: Accuracy of on board trip computor

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Originally Posted by Oldsmokey View Post
Im not farmiliar with Jeeps diesel, but im very familiar with the preformance diesel industry (mostly cummins and duramax motors)

With my 03 cummins powered dodge, any sort of programing would greatly change what the computer calculated. With the dodge and chevys throttle response is changed. Meaning that a half inch of throttle with programing could equal 1 inch of thottle with stock programing. The computer calculates mpg directly from throttle position, vehicle speed and load.

My two cents
It did cross my mind that the "chip" may have a bearing on this, will run it for another week and remove then report back as to results

Its strange but the "real" mpg is actually improving each time I check, todays fill calculates out to 29.06 mpg and thats with some fast 80mph running for several hours yesterday

Does an ECU unit have to "learn" the new settings?
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