View Full Version : E30 Tach mystery

01-02-2012, 09:34 PM
Hey guys, new to this forum read all the rules, did the search read every article i can find of help, and in conclusion i cant find an explanation to this mystery...allow me to elaborate,

I got my 1990 325i, a good 4 months ago, when i bought it, i had no speedo no tach and no mpg and of course the mileage does not work either except for the Temp (twitchy) and gas (fine), which i understand is quite normal for these cars, i know that i needed to check the grounds, maybe its that or the SI board or the Batteries. what i was planning on doing is finding out if its a "GROUNDING" issue first, or Batteries or the SI board....that was the plan.....today heading off to work, i turned the car on waited for it to warm up while i was prepping my coffee, its -28 in ottawa
.......once i got back in the car about to head off i noticed my Tach was working (twitchy) and my MPG is working(fine) but no speedo. I don't understand this because i have not done anything to make it work except unplug and re-plug the diff sensor 2 weeks prior, and it didn't work then...it just started to work out of no where, am genuinely very confused and with this new curve ball i don't know what and where to start from!
any help to clear this mystery would be appreciated just so that i understand what to do next in the hopes of fixing that speedo!

i do have an after market stereo from PO....i heard those can usually affect the cluster.

Thank you guys in advance

Happy new Years!

01-02-2012, 09:37 PM
it can if the wires were butched to make the stereo work if they managed to strip some wrong wires. I suspect it is your SI batteries slowly dying giving their last breath.

01-02-2012, 09:42 PM
Have you tried swapping the Tach for a another one? Try that first. Also, check the grounds like you mentioned. Don't forget to change the fuses as well as blowing one of those will stop your Tach from working completely. I shorted the stereo in my E30 by accident and the fuse blown (If I remember it's #19). That's all the stereo will do lol.

01-02-2012, 09:53 PM
i will go ahead and check that tomorrow, but yea like you mentioned Havoc, i did swap it with a buddy of mine he has an 325is 1988 it bascially did the same thing everything worked(gas) (temp) except the tach mpg and Speedo! just ran outside checked it and fuse 19 is intact

11-10-2013, 04:25 PM
Liquid, have you fixed the issue? I'm having the exact same problem.
- swap cluster to buddy's car, all gauges work ( new si board )
- new diff sensor
- all fuses good
I currently finishing up the head gasket and am waiting for a replacement crank rpm sensor, but can anyone think of anything else to check? Relay?
This issue is driving me crazy.

11-10-2013, 05:35 PM
Xpress i dont usually visit this forum since i sold my e30, but i felt inclined to respond,
from what i recall, the issue was very simple to fix, it all started when i decided to dig deeper and follow the wire harness, from behind the dash all the way into the floorboards, this is what i did.
1. I identified each cable running from the cluster and wrote down color
2. to access the wires that connect to the dash, you need to remove the speaker cover driver side next to the hood release
3. remove the carpet and all the crap around that area, you will notice that the wires(harness) is running under the carpet by the floorboards all the way to the back.
4. BINGO, that is where the problem was, i found that a bunch of wires were corroded or completely cut due to good old age! after stripping and re-wiring everything, and reinstalling the cluster, everything worked perfectly. just make sure to take your time doing this process, some of the wires are really old and some are damaged and could break, in my case i just cut and replaced all the affected parts of the harness, so i don't have to deal with that issue again.

hope this helps buddy! keep me posted

11-10-2013, 07:01 PM
Thank bud.