Min-max resistance of fuel level sender

[Frank818]

What is your resistance when the fuel sender is at the bottom (empty tank) and at top (full tank)?

I think I have a compatibility issue. Shows 95ohms when empty, fuel gauge shows 40% full, but I can't tell if sender is stuck. I have put sealant to prevent the gas leak I had, it's a pain to remove all that.

[THE FURNACE]

Hi Frank,

I have two sending units out of my 05 donor. The one that is attached to the fuel pump reads 51.3 ohms empty and 1.4 ohms full. These are readings directly off the leads. I don't know what the other sending unit is for. Do we install both?

Dave

[Frank818]

Hey Dave,

We install none of the donor's sender cuz we install the one provided by FFR.

Still interesting to see the FFR unit reads outside of oem...

[STiPWRD]

Is the resistance range of your VW cluster the same as the Subaru cluster? I think the Subaru fuel gauge reads 0-90 Ohms.

[Frank818]

That's the thing, the bentley manual explains the values but they are from a vw tool, vw 1301 or something they don't say if it's ohm or another scale.

The range is 50 full to 350 empty, with 160 being half.

Bob answered for the subaru in another thread, it's 0-5 ohms full to 90-100 empty, so my sender is not stuck and showing empty. I then have a compatibility issue with the vw. Crap, that one may be harder to fix right.

[Frank818]

Ok I found it, it was in ohms, it's 50ohms full, 160ohms half and 50ohns empty.

Quite different range. I'm in trouble, yeah.

[STiPWRD]

Frank, all you have to do is put a 50 ohm resistor in series with the sender and you should be all set. It will just read empty slightly early, which is good.

[Frank818]

Is it possible my incompatibility issues through this project can be that simple? :) lolll

IF the scale is really the same way, which is 90-0 for E-F or 350-50 for E-F and not 350-50 for F-E, adding 50ohms means when E the sender will send 145ohms, which is close to the 160ohms = half on the VW.

Wouldn't I need a 250ohms resistance to make it 340 when E?
Then it would send out 250ohms when full, wereas the VW should get 50.
Or I'd have to use only half of the fuel gauge, F to Half, which is probably what you meant?


I still need to verify if VW works backwards than Subaru on the resistance, cuz currently the gauge reads a bit below half. If VW would read 50 as F and 160 as half, at 95ohms like I am now it should read ABOVE half... I see a problem here I need to test first by adding a resistance and see which way the needle moves.

Downsides of trying to fit 2 different manufacturer's components together. :)

[STiPWRD]

I'm not sure I followed all that but I thought you said your VW cluster reads Full at 50 Ohms and empty at 160 Ohms, right? So if the subaru sender, which is just a variable resister, produces 0 ohms at full and 90 ohms when empty, then adding a 50 ohm resister in series will make the sender read full at 50 ohms and empty at 140 ohms.

[STiPWRD]

Just saw that you updated some of the posts (50 full, 350 empty). That does complicate things. You'll have to either buy a different sender (possibly reuse your VW sender) or recondition the resistance range electrically somehow coming from the current sender so it will match what the cluster wants to see. I'm not sure if there's a simple way to do that.

[Frank818]

That's correct sorry I had it wrong at first.

I see 2 "easier" solutions, I could use that 50ohms resistance and use only half of the display, if the resistance goes 50-350 F-E and not the other way around.
I could buy an aftermarket fuel gauge reading 0-90 (couldn't see one reading 50-350, best was 33-240). That's bad cuz I'd have 2 gauges, one not working which means part of my cluster wouldn't be usable and I don't like the idea.

The other solutions are more complex, I could use a full tablet cluster with configurable sensors, that changes everything, is a long way to make it work and a simple fuel gauge would cost me 1000-2000 bucks with that solution.
Another complex one is to convert the 50-350 scale to 0-90. I'm working on that one now, but I still need to check if the resistance is backwards or not compared to Subaru, that would add a lot more complexity I think.
I could change the level sender but how could I find one with 50-350 that would fit in the tank's hole and bottom/up distance.

I'll see if I can find a kit car based on the older VWs or on the VR6 itself (must not be MK4, those are different, need to find based on MK2-3 donor). Maybe they have a solution.

[Bob_n_Cincy]

I could change the level sender but how could I find one with 50-350 that would fit in the tank's hole and bottom/up distance.


Frank
these senders come in different length and resistance values and $56 USD.
You can order custom resistance values.

http://www.dieselmanor.com/isspro/RA9500.asp

Bob

[svanlare]

If you put a 120 ohm resistor in parallel (across the two leads for your sender), you won't get full range, but at least empty will be right---provided I have the empty/full values of 90-0 E-F and 350-50 E-F.

1/(1/350 + 1/120) =~ 89 when empty
1/(1/50 + 1/120) =~ 35 when full

---
Edit: My bad, you are using a VW dash and just need to add resistance, and really won't be able to get where you want. Adding 210 give you

210 + 90 =~ 350 empty (empty reads right)
210 + 0 =~ 210 full (will be between 1/4 and 1/2)

In good news, if the direction is backwards E-F/F-E you should be able to swap the direction of the potentiometer in the tank to fix that.

or buy a new resistor from Bob's link.

[Frank818]

I confirm, it's 350 empty. I added very little resistance and I saw the needle going down. I added a lot of resistance and the needle went to empty. At 95 I am under half, but would expect to be over, according to Bentley. Maybe my stepper motor isn't accurate anyway.

Steve 210+90 is not 350, it's 300. :) I think you meant 260.

I think adding 260 to better see the E is a good idea. I'd stay on the safe side and add 275 or 300, will reach 350 sooner.

Buying just the resistor and keeping the mechanical parts? I can do that? I saw Bob's site with the sender, good idea, would require some fiddling on the gas tank, I'll try to avoid that. But if I have to, then it's a good idea. Now if I can change the resistor only and fit it on the FFR sender unit, that's not too bad!

Since that does not prevent me AT ALL from driving the car and not even passing inspections, for now I'll go with a 225 resistance. Don't forget that FFR sender unit starts to read around half of the FFR tank (not the Boyd), so I'm off no matter the solution here. :)

I have to document this on my thread, in case someone is as stupid as I am to fit a MK3 VR6... lolll And some other VW engines anyway, especially the non-OBD2s, as there is some calibration you can perform with the OBD2.

I'm stupid for stuff like that, but wait until the VR6 fires up and plays its songs... I won't be that stupid then! :D That's pretty much the only reason why I'm building this car, for the engine. And that's not stupid. :)

[svanlare]

Boy I botched it all :eek:... 260 should have been the right answer :)

Being slightly more helpful, most shops will only have 5% resistors and here are the standard resistors values (http://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf)