E34 Erratic Instrument Cluster Function

[ehoe]

My E34 M20 (1989) instrument cluster was having erratic functioning of the gauges recently. The fuel and temperature gauges would swing all the way to the right side (i.e max fuel & temp) then it will return to normal. This happens intermittently only. So came across this link on a possible cause : http://www.bmwe34.net/e34main/maintenance/electrical/capacitors.htm So I dismantled my cluster looking for the capacitors which is the prime suspect stated in the link above that could cause this erratic functions and my cluster is totally different from the picture of the cluster in the link. I don't even have such capacitors on my board. I do however have two large rechargeable batteries on my board. Just wondering anyone know what else could cause erratic functioning of my cluster on my model of cluster?. Has the rechargeable batteries got anything to do with it? What is the function of the batteries in the first place?. Also what is that black little object I pulled out from the back of the cluster? (I highlighted it in a red circle). Any ideas sifu's?. Appreciate the help/advice. Thanks

 

[skinhead]

http://www.bmwe34.net/e34main/maintenance/electrical/capacitors.htm

So I dismantled my cluster looking for the capacitors which is the prime suspect stated in the link above that could cause this erratic functions and my cluster is totally different from the picture of the cluster in the link. I don't even have such capacitors on my board. I do however have two large rechargeable batteries on my board.

i think theres anuther board in ur 1st pic...pry it open...

 

[Nemesis]

OK had a look at the website and the guy there does mention are two types of boards. Is hard to say without a closer inspection but the black object could very well be the coding plug. Which I think he mentioned can also be a cause of erratic operation.

The batteries are for your service indicator memory, and if they have leaked can cause problems.

Ive worked and repaired mainly E30/28/23 boards, and those batteries can wreak havoc, helps if u handy dandy with a soldering iron.

Hope this helps a bit, as not an E34 sifu.

 

[ehoe]

Well my batteries visually looks fine and I don't have any problems with my service indicators so I assume the batt's are ok.

What is the function of the coding plug anyway?. On a digital cluster I would assume it would store things like the odo reading, etc but since mine is an analog cluster so what info would it store. Any ideas anyone.

 

[Nemesis]

The coding plug determines the instruments display values, for example MPH or Km/H, Liters or gallons and also tire size, so the speedo reads correcty.

Basically tells the cluster what car, region etc.