Tach working intermittently.

[zyklon]

Hey guys! I have a wonky tach. It didn't work when I bought the car and never even tried to budge until I replaced the batteries on the SI board. However, even with the batteries replaced and corrosion cleaned up as best I could, it only ever rarely works, and not well.

https://www.youtube.com/watch?v=mlWVNQcxqAA

Getting on the highway one day, my tach started working perfectly. I was so happy!

https://www.youtube.com/watch?v=dCc6-VEE8aQ

About 3 minutes later, of course, the tach stopped working. My buddy Mike who received both Snapchat videos reminded me that I drive an E30 and that's standard shit.

However, I'm fairly convinced it's some sort of shorting issue now.

https://www.youtube.com/watch?v=NCoxehe8xb4

Anyone have any ideas? I'm doing a transmission swap soon, so I can tackle anything underneath, but right now I'm sitting on my hands, not totally sure of what's going on with the thing.

[twiggletwaggle]

Did you check the traces on the PCB? I had a similar issue where my tach and econometer went out, but it was because I used the wrong screws for the cluster surround trim which ended up piercing and damaging some traces. You can see this is a common mistake: http://www.r3vlimited.com/board/showthread.php?t=274422

From what you describe though I'm not sure that this is the issue. My tach went straight to not working after I damaged the trace so no intermittent issues like you had. However, I think it may be worth your while to check. I just soldered some jumper wires in and my tach/econometer works now.

[zyklon]

I did check the PCB, it's all good.

Fun fact: when I wash my car, the tach works for the day. It's definitely a grounding issue, but WHERE is the real question.