Pages: [1]
Author Topic: mk4 fuel sender resistance change  (Read 732 times)
johan99
Newbie
*

Karma: +0/-0
Offline Offline

Posts: 8


« on: January 15, 2021, 07:05:49 PM »

Hello everyone

I have recently adjusted my mk4 cluster, specifically, the fuel gauge so that it is linear, however, that gauge is still not acting linear because I have come to realize that it has to also do with the resistance of the sender unit... I know that around full, the resistance is somewhere around 300 ohms, and empty it's about 50... what I want to do is change the corresponding fuel values for each unit of resistance

Currently, my fuel gauge is sitting on 7/8 mark, which represents 55L according to my fuel gauge linearity (true fuel capacity of a diesel mk4 vw is 64L if it is vented and filled to the top)



However, I know for certain that I don't have 55L in the tank, based on my current fuel consumption and the distance covered since I filled up... I have somewhere around 43L

Vagcom tells me that the sender is showing 247ohms, which corresponds to 55L... I can change the fuel value of 55L to 53L in vagcom under adaptation, measuring block 30, but I can't change it by more then 2L... so basically, 247 ohms = 55L, which i then changed it so that 247ohm = 53L... I want 247 ohms to = 43L

Can this be done?
Logged
tjwasiak
Sr. Member
****

Karma: +25/-0
Offline Offline

Posts: 420


« Reply #1 on: January 16, 2021, 01:13:25 AM »

If it is VDO instrument cluster than it should be doable.
Post dump from the cluster so we can look into this.
Logged
Pynoxim
Jr. Member
**

Karma: +2/-0
Offline Offline

Posts: 45


« Reply #2 on: January 16, 2021, 05:17:59 AM »

The fuel stepper motor reads in steps, and the full sweep of that stepper is around 1400 steps. So take 1400 steps and divide it by the number of lines on the fuel gauge and you'll get the amount of steps per line (Just don't count the first line at empty as that is 0). So eg if there are 8 lines after 0, then 1400/8=175 steps per line. Therefore 7/8ths would be 175*7 = 1225 steps. So on the stepper table put 1225 and on the gauge value table put 55 (of course in its corresponding placements)
Logged
johan99
Newbie
*

Karma: +0/-0
Offline Offline

Posts: 8


« Reply #3 on: January 16, 2021, 01:01:31 PM »

If it is VDO instrument cluster than it should be doable.
Post dump from the cluster so we can look into this.

Yes it is a VDO cluster, see attached
Logged
tjwasiak
Sr. Member
****

Karma: +25/-0
Offline Offline

Posts: 420


« Reply #4 on: January 16, 2021, 01:41:26 PM »

According to my best knowledge:
 - 0x270 (8x1) - 16bit LoHi map (with axis @0x250 or 0x260 - depending if it is FWD or Haldex car) recalculates sender resistance into fuel capacity. IIRC for axis you should use 1 as factor to get values in Ohms, for map values 0.125 converts it into litres
 - 0x290 (8x1) - 16bit LoHi map (with axis @0x280) recalculates fuel capacity into steps for fuel gauge (axis is in litre just as above map, steps without any factor)

I think those should not be covered by any checksum but I may be wrong on that as I did not touch any VW instrument cluster for ages...
Logged
johan99
Newbie
*

Karma: +0/-0
Offline Offline

Posts: 8


« Reply #5 on: January 16, 2021, 06:13:19 PM »

According to my best knowledge:
 - 0x270 (8x1) - 16bit LoHi map (with axis @0x250 or 0x260 - depending if it is FWD or Haldex car) recalculates sender resistance into fuel capacity. IIRC for axis you should use 1 as factor to get values in Ohms, for map values 0.125 converts it into litres
 - 0x290 (8x1) - 16bit LoHi map (with axis @0x280) recalculates fuel capacity into steps for fuel gauge (axis is in litre just as above map, steps without any factor)

I think those should not be covered by any checksum but I may be wrong on that as I did not touch any VW instrument cluster for ages...

unfortunately you lost me there, I have no idea what any of that means except which addresses in the eeprom file you're talking about... my knowledge is limited, hence everything that i've done to my cluster has been with a step by step guide from here or using the tuner pro rt and xdf file
Logged
tjwasiak
Sr. Member
****

Karma: +25/-0
Offline Offline

Posts: 420


« Reply #6 on: January 17, 2021, 06:34:33 AM »

I can try to readjust that for you but I will need you to check sender resistance for empty and full tank as it seems I must have forgotten something regarding sender resistance scaling... Dump contains raw values in range from 264 to 587 for sender resistance and according to that I am unable to get formula which translates 247Ohms into 55l.

EDIT:
Closest formula I got translates 247Ohms into ~42l so it should work as you want but as it does not I must have made a mistake somewhere Sad
« Last Edit: January 17, 2021, 06:38:32 AM by tjwasiak » Logged
johan99
Newbie
*

Karma: +0/-0
Offline Offline

Posts: 8


« Reply #7 on: January 17, 2021, 08:52:31 AM »

Sure that could work, I could always compare the addresses of the dump you edited versus my current one and that would also give me an idea of what is going on. This isn't a must have, it's just a would be nice feature... I will never understand why fuel gauges aren't linear from the manufacturer...
Logged
adam-
Hero Member
*****

Karma: +109/-28
Offline Offline

Posts: 2019


« Reply #8 on: January 17, 2021, 10:48:13 AM »

I will never understand why fuel gauges aren't linear from the manufacturer...
Because they account for the shape of the tank.
Logged
dal
Full Member
***

Karma: +4/-5
Offline Offline

Posts: 149



WWW
« Reply #9 on: January 17, 2021, 12:37:01 PM »

Because they account for the shape of the tank.

+20 karma
Logged

Audi A3 8L
1984cc stroker - E100 - ME7 wideband converted - 400whp target
Instagram: @a3stroker
Pages: [1]
  Print  
 
Jump to:  

Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Page created in 0.019 seconds with 18 queries. (Pretty URLs adds 0s, 0q)