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EVIC % error on MPG
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Author:  mustang_gt_350 [ Mon Jun 14, 2010 2:32 pm ]
Post subject:  EVIC % error on MPG
Just wondering what error you have all noticed on your EVIC vs calculated MPG? This is with a stock ecu or tuned.

I have seen some say .5-1 and others say theres is a much as 3-4 off. The 99 XJ is only around .5 or so off the coulple of times i have checked it.

I only have around 145 or so miles on mine since i picked it up. The dealer filled it so i doubt they filled it the whole way until you can see it so its going to make it hard for me to check this tank by calculation. But so far the EVIC is saying 24.9-25.3. Thats 2lane secondary road driving at around 40-55 mph. In somerset county PA.
Author:  stoutdog [ Mon Jun 14, 2010 3:19 pm ]
Post subject:  Re: EVIC % error on MPG
I'm fairly convinced that the EVIC's accuracy depends on at least three factors: 1) Driving style, 2) Driving condition, and 3) tune/stock.

My stock EVIC was 2-3 mpg high, but I only drove one full tank before getting the GDE tune.... With the tune, my EVIC is even more nuts. It seems to be more accurate (2-3 mpg off) when I do a lot of in-town, stop and go driving and less accurate (5-6 mpg off) when I go on long highway trips. On top of that, if I'm doing a lot of mountain/hill driving - and therefore coasting a lot - the EVIC can climb even higher. Some will call me a lier, but I kid you not, I've seen it read as high as 48.3mpg after about 600 miles of driving and coasting down steep grades, when I really only netted 33.1 or so.
Author:  mustang_gt_350 [ Mon Jun 14, 2010 3:37 pm ]
Post subject:  Re: EVIC % error on MPG
Wow. Thats a huge difference. Looks like i'll be hand calculating mine for sure. I might just fill it on my way home from work in the morning to the neck and go from there.

I had kinda thought the slower you make inputs on the throttle the more accurate it would be, due to i don't know how fast the sample rate of the EVIC is on the throttle position/fuel injected. I know most of the ones i have seen are pretty slow on the display from when you get into the peddle and until it actually shows up on the screen.
Author:  LibertyCRD [ Mon Jun 14, 2010 4:25 pm ]
Post subject:  Re: EVIC % error on MPG
Mine was 1-2 MPG too high. ALL my previous Chrysler vehicles were within 0.2 to 0.5 MPG from being perfect with each fillup. Don't know why this KJ is so far off.

Since the GDE tune, the EVIC is almost useless. At times it's 2 MPG off...but I've seen it as much as 6-7 MPG off. The more time you spend on the highway, the worse it gets too. It's a real shame they weren't able to keep that feature intact with the tune. :cry:
Author:  kdlewis1975 [ Mon Jun 14, 2010 4:50 pm ]
Post subject:  Re: EVIC % error on MPG
When I first got mine, EVIC was off 1-2 mpg for long highway trips. In a mix of city and highway, 4-5 mpg off. After I installed a lift pump, it was always 5-10 mpg. "Off" means too high in all of these cases. With the GDE tune, I'm seeing 4-5 too high for mixed driving. I haven't had it on a good long highway trip since the tune.

They posted before that the calibration for the EVIC is a two point function as they do modify it to make it a bit more accurate. It may be that our fuel return system differs enough from a gasser that a linear fit doesn't quite cut it and a quadractic or cubic fit may be needed.

As we get used to how the fuel gauge moves and how much fuel that represents, one should be able to get a guestimate of mpg. The EVIC seems to serve a "how am I doing?" purpose. I read once that it is a moving averageof the last 60 miles or so of driving or something like that...could be why it varies a lot when driving style is changed. My wife's Suzuki XL7 is usually within 1 mpg for the entire tank. Go figure.
Author:  Ripster [ Mon Jun 14, 2010 9:28 pm ]
Post subject:  Re: EVIC % error on MPG
The updated tune has an update to bring the Evic closer that with the early tune, also turns off the viscous heater
at the first 1/4 mark on the temp gauge. Hope to get mine done next week.
Author:  mustang_gt_350 [ Mon Jun 14, 2010 9:38 pm ]
Post subject:  Re: EVIC % error on MPG
kdlewis1975 wrote:
When I first got mine, EVIC was off 1-2 mpg for long highway trips. In a mix of city and highway, 4-5 mpg off. After I installed a lift pump, it was always 5-10 mpg. "Off" means too high in all of these cases. With the GDE tune, I'm seeing 4-5 too high for mixed driving. I haven't had it on a good long highway trip since the tune.

They posted before that the calibration for the EVIC is a two point function as they do modify it to make it a bit more accurate. It may be that our fuel return system differs enough from a gasser that a linear fit doesn't quite cut it and a quadractic or cubic fit may be needed.

As we get used to how the fuel gauge moves and how much fuel that represents, one should be able to get a guestimate of mpg. The EVIC seems to serve a "how am I doing?" purpose. I read once that it is a moving averageof the last 60 miles or so of driving or something like that...could be why it varies a lot when driving style is changed. My wife's Suzuki XL7 is usually within 1 mpg for the entire tank. Go figure.


However it is doing it i'm sure is different than a gasser. I have noticed if i let off and coast down a small hill i will usually gain .1-.2 just withing a 1/4mile coast or less sometimes. The XJ i can coast off and on a few miles and only have it go up .1 or .2 and the same with the 2 09 and 10 focus' that i have ridden in on our way to work, they are the same .1 or .2 change over a few mile decent with some flat and small climbs.
Author:  stoutdog [ Mon Jun 14, 2010 11:05 pm ]
Post subject:  Re: EVIC % error on MPG
Ripster wrote:
The updated tune has an update to bring the Evic closer that with the early tune, also turns off the viscous heater
at the first 1/4 mark on the temp gauge. Hope to get mine done next week.

This helped a little bit. The worst I've seen since getting the update is about +9mpg. It's usually within 5mpg or so now...
Author:  mustang_gt_350 [ Mon Jun 21, 2010 8:43 pm ]
Post subject:  Re: EVIC % error on MPG
Ok Just hand calculated my first tank. Now i did not fill it so i'm just guessing that the salesman filled it until the pump kicked off. I couln'd get the nozzle down in the tank more than about 2" this is the first time i have had this problem that little spring around the outside if the nozzle hit the filler hole. It calculated out to almost 21.6mpg, but its hard to say exactly since i was not the one to fill it and if she got the nozzle in the whole way until it kicked it would have been probably about a gallon less which would have been 22.8. There is a lot of chance of error on that style though. The evic said i think 25.3 or 24.9 i can't rem. This time i filled it to where i could see it on the neck and when i fill it again i'll use the same pump and pull in from the same direction.

Summary

17.8 gal 406 miles= 21.6
18.8 gal 406 miles= 22.8
EVIC= 24.9

I ended up putting 21.2 gal in it when i filled it up into the neck.
Author:  LibertyCRD [ Mon Jun 21, 2010 9:56 pm ]
Post subject:  Re: EVIC % error on MPG
That sounds very realistic, and is perfectly in line with what almost all other CRDs are getting according to Fuelly.com...contrary to the magic 35 MPG some folks here are claiming.

My fillup yesterday revealed an honest 24.2 MPG (EVIC showed 26.5)...which is one of my better tanks so far. I worked for it too. It's awful driving that slow. Once my new t-stat is installed, I hope to pick up 1 MPG more.
Author:  stoutdog [ Mon Jun 21, 2010 11:00 pm ]
Post subject:  Re: EVIC % error on MPG
LibertyCRD wrote:
That sounds very realistic, and is perfectly in line with what almost all other CRDs are getting according to Fuelly.com...contrary to the magic 35 MPG some folks here are claiming.

My fillup yesterday revealed an honest 24.2 MPG (EVIC showed 26.5)...which is one of my better tanks so far. I worked for it too. It's awful driving that slow. Once my new t-stat is installed, I hope to pick up 1 MPG more.

You should pick up more than 1mpg, IMO. I've driven two nearly identical CRDs (mine and my father's) on nearly identical routes, at the exact same speed. His has a bad tstat, mine does not. Whereas in my Jeep I netted a real, GPS adjusted, hand-calculated mpg of ~34 on that drive, in his I only managed a shade under 30. His Jeep felt noticeably sluggish and less responsive... think about it, your Jeep is spending 100% of your driving time operating at about 20*F under peak operating temp. That's almost as bad as on your mpg as driving three miles to and from work in the wintertime... your Jeep is never operating at optimal efficiency.
Author:  mustang_gt_350 [ Tue Jun 22, 2010 9:04 am ]
Post subject:  Re: EVIC % error on MPG
I'm hoping to get into the 24mpg range driving to work, and get into around 27hwy. Driving it as lightly as i do i don't think it should be a problem. I could get around 18 driving around the area and between 20-21 hwy with my 7200lb powerstroke. thats filling it at the same pump until i could see it for the 1-2 years i drove it as a DD. So i'm hoping i can get the 24/27hwy. I'm not a speed racer on the hwy.

I still have the muffler delete mod left on my to-do list. Then I will probably put on a boost gauge and make sure i have no leaks. Then EGT and trans temp to get ready for the GDE econo tune that will be the last mod other than HID lights and some small things.
Author:  MrMopar64 [ Tue Jun 22, 2010 9:31 pm ]
Post subject:  Re: EVIC % error on MPG
The accuracy of the EVIC depends on two things: accuracy of the fuel flow rate (L/hr) and that of the vehicle speed.

Accuracy of the fuel flow is based upon the quantity and rail pressure, but of course you must also consider the drift of the specific components in your vehicle. not all components wear the same and at the same rate, and so in these older applications sometimes the accuracy of this drifts over time, especially as the vehicle ages.
Author:  mustang_gt_350 [ Tue Jun 22, 2010 11:16 pm ]
Post subject:  Re: EVIC % error on MPG
I did some testing tonight. I put about 75 miles on it with the garmin on board for all of it. I had 9.99 miles showing on the gps, and 9.5 on the trip. So thats 5% error. And after 75 miles the difference still calculates out to like 5.03% or so. So that means my trip/odometer is reading 5% less than i actually traveled.

And MY speedo is reading about 2-3mph fast, 2 on anything less than around 55 and closer to 3 over 55 up to 75 (secondary roads couldn't get anymore speed in the straights and have it stabilize before i had to back off)

So my fill up with 406 miles would have been 426.3 gps miles

I have 96 miles since my last fill up and the EVIC is still saying something in the 540s until empty, and the gauge hasn't moved.


About the accuracy, i honestly have never heard of anyone with a diesel and a MPG display say theres was right. All of the powerstroke guys that have them say they are worthless, and pretty much seams to be the common statement with the crd also. Maybe its harder to actualy monitor these engines. I wouldn't think it would be so hard to have a really accurate calculation since the ECM knows exactly how much it is injecting on each injection event, they just were lazy when programming the feature.
Author:  flash7210 [ Wed Jun 23, 2010 9:47 am ]
Post subject:  Re: EVIC % error on MPG
I dont have an EVIC so I do all my MPG calculations by hand.
And yes, the odo counts fewer miles when compared to GPS. I calculated my error to be ~4%.
To make the math simple, for every tank over 500 miles I just add 20 miles and calculate MPG
from that.

Also, now that I have taller tires, my speedo reads about 2 mph slower than actual.
Author:  LibertyCRD [ Wed Jun 23, 2010 9:52 am ]
Post subject:  Re: EVIC % error on MPG
My speedo/odo was 2% FAST when I bought my CRD. I had to subtract miles from the trip meter to do a proper hand calculation.

Now, with the 255/70s... my GPS indicates that I'm 2% slow, so I'm adding 2% to all my MPG figures to get an accurate reading.

2% error is not bad at all though, in either direction. You have to think... even bald tires will change the odo some, and improperly inflated tires can have a big impact on the odo too. So everyone is going to have a slightly different experience here.
Author:  mustang_gt_350 [ Wed Jun 23, 2010 9:59 am ]
Post subject:  Re: EVIC % error on MPG
Generally what PSI do you guys run in your 225/75/16's The previous owner had a set of coopers put on and i have been meaning to check them but havn't yet. They look to be wearing well so they might be right on.

My evic after 106 miles is saying 514 until empty. Thats with it showing 27.2 avg.

Either way i'm still very happy with how it runs, i HATE the 3.7 libby's. And its still beating the gasser libbys from most of the numbers i have seen for MPG by a fair amount.Actually the crd is the only reason i even considered buying this one because if they didn't make them in the CRD i would be driving another XJ.

Going to try to chop off the muffler tonight and straight pipe it if time allows.
Author:  LibertyCRD [ Wed Jun 23, 2010 1:20 pm ]
Post subject:  Re: EVIC % error on MPG
mustang_gt_350 wrote:
Generally what PSI do you guys run in your 225/75/16's The previous owner had a set of coopers put on and i have been meaning to check them but havn't yet. They look to be wearing well so they might be right on.

My evic after 106 miles is saying 514 until empty. Thats with it showing 27.2 avg.

Either way i'm still very happy with how it runs, i HATE the 3.7 libby's. And its still beating the gasser libbys from most of the numbers i have seen for MPG by a fair amount.Actually the crd is the only reason i even considered buying this one because if they didn't make them in the CRD i would be driving another XJ.

Going to try to chop off the muffler tonight and straight pipe it if time allows.


I would run the tires about 36 psi. I think the door tag says 35...but I go up 1 or 2 psi more usually to allow for some temperature fluctuation.

After driving CRD #2 for a while with a straight pipe now...I can confirm that there is ZERO MPG benefit from having the muffler gone. The only thing I'm noticing is that the coasting ability is better.
Author:  mustang_gt_350 [ Wed Jun 23, 2010 6:48 pm ]
Post subject:  Re: EVIC % error on MPG
I checked right after i posted and there is 36psi in them.

I'm mostly doing the exhaust mod because i'm into louder stuff, its too quite. That and i coast a fair amount when i'm leaving my house but i have to keep my foot on the throttle a little. I want to see if that helps me out a little there.
Author:  LibertyCRD [ Wed Jun 23, 2010 6:56 pm ]
Post subject:  Re: EVIC % error on MPG
10-4. So what model of Cooper tire is that you are running? Is it the Discoverer ATR?
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