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Bmw e28 Speedo issues


Nmaisey

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Hey guys. After a bit of help please. 
 

I have an e28 bmw. Am running link g4+. Was all set up by a qualified person. However the Speedo never worked. 
 

after a lot of research the Speedo was connected directly to the speed sensor on the diff. I had changed diffs to an z3 diff with lsd. Swapped speed sensor over from my old diff. My guess is that the new diff speed tabs were different to what the Speedo was set up to read and it just didn’t work. 
 

so

 

I have now intercepted the speed sensor circuit and have this put to DI2 on the link. Aux4 is setup to speedo out and this runs back to the speedo. I have DI2 setup as “GP Speed” 
 

the speedo now works but I am getting a fluctuating needle. It jumps around a bit. 
 

I have tried changing between rising and falling settings with little to no difference. I have played with the calibration settings and multiplier and they make a difference but the needle still randomly jumps around as the speed climbs. 
 

I have noticed that the needle jumps in line with a fluctuating frequency reading in the live data table from the DI2 input. But I don’t know what is causing this or how to remedy it. 
 

can anyone help with my setup here? Anyone had similar issues with bmws? I know the e30 and the e28 have a similar setup (for those that have had success with e30s)

 

thanks in advance for any advice. 
cheers

Nathan 

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Actually those look like a reed switch, so basically when a blade passes through the gap a contact is magnetically closed, when there is no blade the contact springs back open.  If it is anything like the Toyota and Nissan ones from the similar era it is likely just end of life, the contacts either get sticky or slow to close so you get the erratic speed signal.  

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