OBC Problems

Wed Aug 26, 2015 11:01 am

I have just retro-fitted a 13 OBC to my '88 325is, but it has some problems:

1) The cruise control no longer works. I thought that maybe I had dislodged a wire from the column control or under the dash or something equally silly, but I checked everything and no obvious problem. The "kit" came with a green plug for the instrument cluster with the loop wire already fitted. I checked the part number, and being the same as the one already in use, I just swapped them over.

2) The temperature read out is consistently 3 degrees hotter than the actual temp. Is there a way to calibrate this out?
Also, I'd like it to be in F, but will only show in C.

3) I got the clock function to change from "heur" to AM and PM, but I can't get the unit measurement to change from metric to imperial. I like MPG not L/100K, but it won't change over as per the owners manual. Any ideas?

4) The distance to empty is not even in the ballpark. When it is about to run dry, it still thinks there is 60K to go, and a full tank elicits an optomistic "500k" when infact I have never got better than 350k on a full tank.

Incidentally, my tank only holds 50 litres. I know that for a fact, yet it looks identical to the correct 60 litre tank for the car (I had it out during the rebuild). Any ideas?

Wed Aug 26, 2015 11:27 am

Giddyup58 wrote: Incidentally, my tank only holds 50 litres. I know that for a fact, yet it looks identical to the correct 60 litre tank for the car (I had it out during the rebuild). Any ideas?

How do you know it only holds 50l?

Be brave and run the tank lower and you'll get more than 50l in. (Keep a jerry can of fuel in the boot just in case lol)
The tank will be a 63l tank unless it's been swapped for a 55l for some strange reason. Even with the needle in the red on mine (63l), I usually only get 52l-53l in. The most I've managed is 59l shortly after the fuel light came on.

Wed Aug 26, 2015 11:50 am

I ran it out of fuel - accidentally I may add - the low fuel light was only on for about 3kms - but by pure chance I managed to coast into a fuel station. It took 50 litres to fill. I remember thinking that it it must have a 318 tank in it, but then I remembered what it looked like, and it def. seemed to be the big tank. Two holes in top, one for sender unit, the other for in tank pump. Level across the bottom - looks like a 60 litre tank. Only holds 50...

Another gremlin with the OBC: The gong doesn't work. Before I hooked up the temp sensor, the default reading was -30 C, so it should have gonged for Ice. Also, I have set speed alerts all over the place, but it wont go off.
Is it supposed to go off for doors ajar, lights on and that sort of thing?

Thoughts?

Wed Aug 26, 2015 2:22 pm

You run out of fuel when the level drops enough for the pump inlet to suck air, not necessarily when the tank is empty. Check that your pump is as BMW intended, and not some aftermarket effort with the pick up too high.
OBC gong can be tested independently. Hook up the + and - 12 volt supplies to it, then shorting the third wire to - (I think) should make the gong sound once.
Standard E30 gong doesn't work for lights on/ doors open etc., mainly because it doesn't have a permanent live supply, but there is a gong available (Probably E34 or E36) that has the socket for the E30 plug, plus a second socket that has a pin for a permanent live, and a pin, which when grounded, makes the gong strike repeatedly - ideal for lights and doors.

Wed Aug 26, 2015 4:59 pm

Try pressing 1000 and 1 to see fuel remaining.

I think the coding plugs determine this as I have does the same retrofit (minus cruise control) and it reads my tank as 55L when I know it is 63L.

Thu Aug 27, 2015 2:40 am

I pressed the 1000 and the 1 together, and it came back with 5.0, and hasn't moved after a 5k trip. The fuel gauge reckons about 15litres and the distance to empty is saying a bit over 50, which may be somewhat correct, given that the average consumption is 9.8/100k.

It also puts the wrong fuel pump theory on the back foot, which is very disappointing as I know it has an aftermarket pump and the theory made a lot of sense. I'll open it up and do some careful measuring...

Thu Aug 27, 2015 2:39 pm

Try pressing 100 and 1 together, it will show the OBC coding plug type.
Maybe the one you have is not compatible with your engine.

Sat Aug 29, 2015 8:21 am

Pulled the dash out today. Some weird wiring loop on the green Cruise Control insert. Took it off, cleaned every contact I could see and tried again. Cruise control now works! Happy days.
Only problem - lost the swing-o-meter.
It goes to the far right under full throttle, and sits hard to the left for the rest of the time.
Behind the dash is the green C/C insert. A blue wire with yellow trace which is the speedo feed to the C/C computer plugs into it in one of 3 possible positions.
Can anyone tell me if it is critical as to which of the 3 identical receptacles it plugs into?