OBC: Fuel and Speed

[karl1171]

I retro fitted an obc to my 91 525iSE manual (UK). I get no information regarding average speed consumption range etc.

I've checked wiring diagrams and noticed the fuel level sender appears to be a parallel connection with the instrument cluster. I've checked the wiring and have continuity between the OBC and cluster, so if my fuel guage works why do I get no info on the obc?

I've also gone into the test functions which show remaining fuel in the tank: zero fuel level shows on here.

Ive also checked the continuity between the obc and cluster for the speed. This is an output from the cluster rather than in paralel with the speedo sender so can't confirm if this is working. Speedo works on the cluster ok though.

On the test functions there is another function to show voltage - this also reads zero, so dont know if this provides any clues.

The obc is receving power on the correct pins, and the clock and temperature work ok (already fitted outside temperature sender)

I have tried a different obc as well but get the same symptoms

I understood no coding plug was required for the 525 OBC. Is it possible the problem may be related to the coding plug on the instrument cluster?

I'd be grateful for any tips!

[Mr Project]

There's also a real-time speed sensor voltage readout test function in the OBC, have you tried that? Unless that is what you mean by 'voltage readout', but I thought you meant the Alternator/Battery voltage test function.

[karl1171]

I did mean the battery voltage, function 9 on the test. I guess that only shows when you turn the ignition on (d'oh!) I've just tried the speed reading (function 8) which reads zero.

[Mr Project]

I just gotta ask one more stupid question, you did the speed test with the car moving, right? It will show 0v at a stop.

If it's showing 0v while moving, then you've found the problem, which is that the OBC isn't getting the speed reading. If you're sure the wire is good from the cluster, then I guess you're stuck with something being wrong in the cluster itself. I'd start by replacing the famous capacitors since they're a known issue (and cheap), resolder any bad-looking connections on the board, and then worry about detailed troubleshooting of the board afterwards if that doesn't fix it.

[RichG]

I'd start by replacing the famous capacitors since they're a known issue (and cheap), resolder any bad-looking connections on the board , and then worry about detailed troubleshooting of the board afterwards if that doesn't fix it.

I have a stock (as far as I know) 1990 525i and have the exact problems Karl1171 is describing. Speedo, outside temp, fuel gauge, clock all work, but mileage computations and cruise control don't. Not sure if cruise is related, but if it's not computing avg fuel etc. it seems it's not getting some signal about current speed even though the speedo is working.

What and where are the famous capacitors and which board could need resoldering?

Thanks

[Mr Project]

http://www.bmwe34.net/e34main/mainte...capacitors.htm

I'm about to do this myself to see if it helps the fuel guage issue I have now, and a flickering odometer.

When I say resolder the board, it's just my habit that when I've got an old dashboard torn down to replace components, I examine all of the soldered components and wires carefully to see if any of the solder joints look "Cold" (dull) or cracked, or even burned. If I see any problems, I'll remove the old solder and re-do it with new flux and good quality solder. I'm degreed in EE, so I'm fairly handy with a soldering iron and can usually spot the problem areas, but any careful examination with good lighting will be worth your time while you have it apart.

[karl1171]

Hi yes I did try the speed function with the car moving: 0 volts

With regards to the capacitors I had to replace them when I first got the car (before I attempted the obc) as the speedo didnt work on cold mornings. It successfully fixed that problem, as for further dry joints its quite a detailed board, I suspect a trip to the breakers may be an easier option!

I received a message form another contributor from an earlier post who mentioned the should be a fuel remaining sensor: I dont know if this is part of the fuel gauge sender or an additional part. However I'm not sure if this is definitely the case as the circuit diagram (from www.e38.org/e34) appears to show the sender form the fuel tank as being a parallel connection between the cluster and the obc.

Hmmm!

(by thr way I was referring to me being stupid with the voltage test! )