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Discussion Starter #1
Hey guys n gals.

I just found this on the net, havnt seen it on this forum before so thought i might post it up, going to try it tomorrow as my Range and MPG are out.

A. IF YOUR CONSUMPTION AND RANGE VALUE IS OFF DO THIS:

1. Unlock the unit. Google this or Search it-I'm not going to repeat it here.

2. Run Test #5 and write the number you see down. It will be your RANGE to empty in Kilometers based on the two information values stored in the OBC. These are CONSUMPTION RATE and REMAINDER OF FUEL IN TANK. If your Consumption Rate is off then this number will be off as well.

3. Run Test #7 and write the number you see down. It will be your exact FUEL in your gas tank in Liters based on information directly from your Fuel Level Sensors. This number is always correct.

4. Run Test #20 and write the number you see. It should be 1000 or a number close to that value. This is the OBC's default or previously set Correction Factor value.

5. Go to Find a Car and find your Car, get your New EPA MPG Estimate for Combined MPG (for example a 1995 318i is 18 City-26 Highway and 21 Combined-You will only use the Combined Value) and write number down.

6. Now get out a pencil and a calculator. You will now compute the Correction Factor for your OBC. Basically you will use the actual MPG for your car to change the Value of 1000 that is stored in your OBC.

7. Find your the OBC's incorrect MPG Value; Start by multiplying your Fuel Remaining in your Tank from TEST #7 by 0.26 to get the Fuel in Gallons. Then multiply your Range Value that you got from TEST #4 by 0.62 to get your Range in Miles. Now Divide the Range (miles) by the Fuel left in your tank (gallons) to get your OBC's MPG which should be incorrect. Now divide this MPG by your car's actual MPG-The Combined Value you got from the EPA website. You should get a low number like 0.590 or thereabouts. Now multiply this number by the Correction Factor Value that you got from TEST# 20. The number you end up with is your new Correction Factor Value.

8. Return to TEST #20 and use your 1000/100/10/1 Keys to reset the value to your new Correction Factor Value* that you just calculated. Hit Set/Reset and there you go. Your Range and Consumption should be fixed.

NOTE: If you find that your Correction Factor is not allowing you to input a number less than 750 then your OBC needsto be recoded at the dealership.



Also, you can set the OBC for your car, I changed mine to 328i (it came from a 325i) and only things i really noticed that changed is my date went from mm/dd to dd/mm which i prefer, and clock also went to 24hr :D See below:

E36 325i '94: EINHEIT1: 71, EINHEIT2: FF.
E36 320i '94: EINHEIT1: 7B, EINHEIT2: FF.
E36 328i '95: EINHEIT1: 71, EINHEIT2: 77.
E36 328i '95: EINHEIT1: BA, EINHEIT2: FF.
E36 M3 '97-98 EINHEIT1: B3, EIHEIT3: FF.
E36 320i '92: EINHEIT1: 04, EINHEIT2: FF.
E36 325i '92: EINHEIT1: 71, EINHEIT2: 77.

Upon reading up some more it seems that these codes stand for Unit 1, Unit 2. They are mainly for check control set up. EINHEIT1 is danger codes (IE tail lights, coolant level) and EINHEIT2 is for things like washer fluid low...

I changed mine from 71,FF to the 328 setting above of 71,77. As said above it changed my date and time format but nothing much else. I did get a washer fluid low warning after i done this and it turned out my washer fluid was actually getting low so i can only assume i done the right thing by changing code 2.

Obviously if you are going to try changing your EINHEIT settings i suggest writing down your starting figures as it seems you can cause some problems if you put the wrong ones in and there are over 3000 combinations so you can spend an age trying to find your original settings that work.

From internet searching it seems that B7,FF are for check control delete for if you installed the OBC on a not check control equipped car and are getting a 'check control inact' warning.

I dont know how useful or meaningful this info is to every one but i find it quite interesting and like the fact i can get the OBC perfectly tuned to my car :)
 

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I was looking for this info a few months back, and couldn't find it again - So thanks for posting :thumbsup
 

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Discussion Starter #3
Yea it turns out its quite hard info to find! Glad to have helped :)
 

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Bump. I thought people might like this? Lol, maybe its just cuz I know alot less that every one else?
 

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What if you want to customise it to your car?
As in, I can physically calculate the MPG I got on my last run, what if this doesn't tally with the MPG reading on the OBC?
 

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Discussion Starter #6
Go through the first steps of my first post and that should do it. The only way to really work it out properly yourself is to run the car to empty, put exactly 1 gallon in and reset ur mpg, then run ur car to empty and compare the OBC mpg to the amount of miles travelled since u put the gallon in. Wouldn't ever want to do it tho cuz uv Gota run ur car empty twice..
 

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The way I do it is to brim the tank, drive around, then brim it again.
Then you have the miles you covered on exactly how much fuel (to the first click each time you brim it.) Just wondered how to compare when I finally get my 18 button in as I'm guessing it's going to be way off.
 

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Discussion Starter #8
Ah i see. Thats a good idea. Im not sure it will be WAY off. Mine seems to be a bit ambitious with my range considering its giving me quite a low average MPG. I have left it a while and the range does seem to be right within 15-20 miles but if i can get it closer i will. I took mine out of a 325 so the fuel consumption wouldnt really have been too different. I guess if u take the OBC out of a car with a hugely different engine size then it would be further out? Not 100% sure because it uses the same equation to work out MPG on any car but the fact there is actually a calibration factor built in just points out to me that there is a possibility for error.
 

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OK I'm sat in my car right now having done this and one thing:

When they say you have to divide the fuel left in the tank by 0.26, that's for US gallons. Here we need to divide it by 0.22.

With that done I've got the correct MPG figures showing on my OBC based on the physical calculations I got.
 

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The way I do it is to brim the tank, drive around, then brim it again.
Then you have the miles you covered on exactly how much fuel (to the first click each time you brim it.) Just wondered how to compare when I finally get my 18 button in as I'm guessing it's going to be way off.
Brim, reset trip, do miles, them brim again is the best way to work out your actual MPG.

Now if at the same time as you reset the trip on the instrument cluster you reset consumption 1 (or consumption 2) all you have to do is look at the consumption 1 (or consumption 2) value when you fill up, then calculate MPG and compare to get your actual and OBC figures.

(None of what I have written above helps you with the correction factor yet I'm just throwing it on the page)


Now test #5 goves you the range in kilometeres, as does pressing the range button and then the km/mls button to flip from miles to kilometers and back.... so as thes two show the same info no point really converting test #5


As anyone who has an OBC knows range figure is very volatile and not really a good indication as it only uses a few data points at a guess.



Looks to me like you can do what I said above to get the OBC MPG and your real MPG.

Then divide the OBC MPG by the real MPG and times that by the correction value factor found in #20

Should be a lot more accirate than the highly volatile range figure that will fluctuate easily with 30 seconds boot up a hill.
 

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Also step 7

If your OBC is reading high and the actual MPG is low, how can you get a value of less than 1?

Have I missed something?
 

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The below seems to back up my opinion that a lot of those calculations are not required because the information is already presented by the OBC

The red text below pasted into notepad or any other text editor (the plainer the better) and saved as anything you like with a .vbs extention e.g. correction.vbs will work on most Windows boxes to do the calculations for you. Any mistakes in it let me know.

No warranty of any kind implied or given and no liability for any loss or damage, no matter how incurred accepted.





'First line of script, paste into text editor and save as whateverYouLike.vbs
'Works on most windows boxes
'No warrant of any kind implied or given

Option Explicit

Dim varTest5 'range in km
Dim varTest7 'tank in litres
Dim varTest20 'correction factor
Dim varRangeButton 'range button figure on miles
Dim varOBCMPG 'taken from OBC display
Dim varActualMPG 'taken from brim to brim for example.
Dim varCalculatedMPG
Dim varCalculatedRange
Dim varLongwindedCorrection
Dim varObviousCorrection


Wscript.Echo "No warrant of any kind implied or given"

varTest5 = inputbox("Range in kilometres","Test 5", 96)
wscript.Echo "You do realise you could have got that" & (Chr(13) & Chr(10)) & "from the range button by hitting mls" & (Chr(47)) & "km don't you?"
varTest7 = inputbox("Contents of tank in litres","Test 7", 9.3)
varTest20 = inputbox("Current correction factor","Test 20", 1000)
varRangeButton = inputbox("Range in Miles from OBC range button","Range", 60)
varOBCMPG = inputbox("Current MPG from Consum 1 or Consum2","OBC MPG", 28.3)
varActualMPG = inputbox("Actual MPG from a Brim to Brim","Actual MPG", 25.5)

'converions
'1 litre = 0.219969157 Imperial gallons
'1 Imperial gallon = 4.54609188 litres
'1 kilometre = 0.621371192 miles

varCalculatedRange = (varTest5 * 0.621371192)

Wscript.Echo ("Test 5 range " & varTest5 & " km times 0.621371192 " & (Chr(61)) _
& " " & varCalculatedRange & " miles" & (Chr(13)) & (Chr(10))& "The value from the range button was " & varRangeButton & " in miles")

varCalculatedMPG = varCalculatedRange / (vartest7 * 0.219969157)

Wscript.Echo ("Test 7 lites " & varTest7 & " times 0.219969157 " & (Chr(47)) & " " & varCalculatedRange & " " & (Chr(61)) & " " & varCalculatedMPG & " MPG" & (Chr(13) & Chr(10)) _
& "The value from Consum 1 or Consum 2 was " & varOBCMPG & " MPG" & (Chr(13) & Chr(10)) & "Consum1 or Consum 2 are less volatile and more likely to be accurate")

'(MPG from tests divided by real MPG ) * correction

varLongwindedCorrection = (varCalculatedMPG / varActualMPG) * varTest20
varObviousCorrection = (varOBCMPG / varActualMPG) * varTest20

Wscript.Echo ("The long winded way..... calculated MPG " & varCalculatedMPG & " " & (Chr(47)) _
& " actual MPG " & varActualMPG & " times correction factor " & varTest20 & " " & (Chr(61)) _
& " " & varLongwindedCorrection & (Chr(13)) & (Chr(10)) & "The short way..... OBC MPG " & varOBCMPG & " " & (Chr(47)) _
& " actual MPG " & varActualMPG & " times correction factor " & varTest20 & " " & (Chr(61)) & " " & varObviousCorrection)

'last line of script
 

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Incidental point:

The OBC Consum 1 and Consum 2 are not calculated using the fuel tank reading at all.


(Seeing as the ECU knows how long the injector pulse is and the pressure the volume can easily be calculated from that, and we know the OBC has access to that info from Test #2)
 
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