OBC functions and fuel gauge problems

[dpehlivanov]

I have some problems with the obc functions that show you the amount fuel in the tank (1000 + 1) - it always show 5.0 L, but i have more. It stays on 5 liters even when i refuel the car. Same with the Range function - it stays on 50 kms always. Where is the problem?

Also when i changed the obc display i saw an yellow cable which goes with the obc installation, but i couldn't find where it is from. What is it for?

And the second problem is with the fuel gauge. It works, but when i refuel the car the needle moves just a little bit. Yes, it moves, but not enough. Can i fix it somehow, because i don't want to search for a signle fuel gauge?

Thanks and sorry for the bad english.

[SGP]

Hi, you may need to re-calibrate your OBC scroll down to "Inaccurate Fuel Range" on this page.
http://www.e30zone.net/e30zonewiki/inde ... d_Computer
As far as I know all the wiring for the OBC is on one plug, the yellow is for an electric aerial from the radio, but I might be wrong on this.
Re. the fuel gauge, you may have a loose earth on the back of the gauge, it's a brass nut, that needs to be tightened.

[dpehlivanov]

Tried to reset the OBC. I drove until the light for the reserve fuel turned on. As we all know that means that there are 6 liters remain in the tank. Then i stopped, reset the OBC, and tried again the 1000 + 1 function. For a while it was 0.0 L. Few seconds after that it turned back to 5.0 L and it's not moving. Also couldn't figure out the calibrating thing with the screw driver, it always stays on 5.0 L. Tried how the Range function is after the reset. Well there was some movement. From 59 it went 47 KMs, but it doesn't seemed to be correct. After a little it went back to 50, etc... it doesn't seemed to be correct.

Is it possible to have some problem in the tank?

[BenHar]

I suspect that you need to sort out the fuel gauge to get the OBC will work.

Ben

[dpehlivanov]

Well, what can be the problem of the gauge? Like i said it works, but the needle is moving very slow and slightly. If i put 10 liters in the tank it moves with 2-3 mm's... Is it the fuel level sender unit or the gauge?

thx!

[Brianmoooore]

I suspect that you need to sort out the fuel gauge to get the OBC will work.

Ben

Almost certainly. If the fuel gauge isn't working, then the OBC probably isn't getting fuel level info. either.

Pull up the rear seat cushion, find an eight pin plug and socket at the RH side, which should be cable tied to the vent pipe tube, and pull it apart.
Switch on the ignition, take the half that connects to the loom running across the back seat, and use a piece of wire to connect together one of the brown wires and the brown/grey wire.
The low fuel warning should light up.
Now use the piece of wire to link one of the brown wires to the brown/green wire. This should make the fuel gauge read full.
Post back here if this works.

[dpehlivanov]

Yes, it worked! Connected 1st brown cable to the brown/grey and nothing happened. Then tried with the 2nd brown cable again to brown/grey and the fuel warning lighted up.
Connected again the 1st brown cable, but now to brown/green, nothing happened again. Tried again the 2nd brown cable to brown/green and the needle moved somewhere between 20 and 30 liters* (i don't know what is the exact amount of fuel in the tank).

So everything you told me worked, but isn't it strange that nothing happened when i connected 1st brown cable with brown/grey and brown/green, only the 2nd cable worked with them? What should i do from now on? Sorry for the stupid questions i'm really not into the electricity.

* - i'm not really sure that the amount of 20-30 liters that the needle shows is correct. Today when i got back from work the fuel warning lighted up, like i have about 6 liters left, then on the gas station i charged with arround 6-7 liters more, but i believe (not 100% sure, but i believe) that i don't have so much fuel. Which is more possible - the fuel warning indication is not correct and it lights up when i have more fuel (10-15 liters for example) or something with the gauge is not right and it shows more fuel than i really have? Or the gauge and the fuel warning sensor are ok and i really have that amount of fuel?

Thank you, guys?

[Brianmoooore]

Looking back at your first post, I see you asked a question about the OBC wiring. There is a single yellow wire with a white connector on it, near the OBC itself, which is unused. There are also a two pin plug under the bonnet , near the fusebox, and another one in the cabin near the accessories socket that are also unused.
Before I go any further with the fuel gauge problem, I need to know what model and age of E30 you have, since there are differences in the wiring that may be relevant.
The brown wire that 'worked' should have been the one on the corner of the plug. The wire next to this one is brown/red and the next one again should be the other brown. This brown and brown/red carry the road speed signal from the diff., and go all the way to the white plug on the instrument cluster.

[dpehlivanov]

The car is german 320i touring '90, hope this helps. Thank you.

[Brianmoooore]

Tried again the 2nd brown cable to brown/green and the needle moved somewhere between 20 and 30 liters*

This isn't quite what should have happened. When the brown/green was connected to the brown, the gauge should have read completely full. The actual amount of fuel in the tank is irrelevant.
The low fuel light is usually very reliable, and it's likely that when this comes on you do actually have around 5 or 6 litres left.
Your touring will have a 62 litre fuel tank, and this has two fuel level senders, one in each side of the tank. Each should have a resistance of about 60 ohms when the tank is empty, and close to zero ohms when it is full. The two senders are connected in series, so the total resistance should be 120 ohms for an empty tank and zero ohms for a full tank.
The senders are located under two inspection covers in the rear seat pan, but to get at these on a touring, you need to remove both seat bases, the bar that the seats hinge on (three small grub screws), and the carpet that covers the seat base.