Author Topic: Flakey speedometer needle (Read 3207 times)

Geoff · « **on:** September 22, 2011, 06:33:28 PM »

Greetings, on my 91 318is, the speedometer needle works about 1/2 of the time. When its not indicating speed, the odometer continues to turn.
When it stops working, it just suddenly falls to zero. When it comes back on, it will jump once to like 60, then fall, then work normally again for a while. The car can be sitting stopped, the needle will still jump, then work normal after that. Before I dive into the instrument cluster of a new (to me) car, does anyone have any sage advice? I know you can tell speed by the tach, but its still nice to have all the stuff working right.
Thanks,

Geoff

DesktopDave · « **Reply #1 on:** September 22, 2011, 08:08:59 PM »

Not sure myself. I'd guess that it could also be the sender in the diff. Mine does that dancing during the winter, but works just fine when it's warm outside.

Might be capacitors in the mainboard too. Do your SI board LEDs light up correctly?

Geoff · « **Reply #2 on:** September 23, 2011, 05:37:17 AM »

From what I can tell, all lights and indicators are working, except the speedo needle. From the stack of service records, I see the sender was replaced in 2010, and it does look new. Does the sender send out different signals for speed and distance, or just one signal ? I thought since the odometer is working, the sender was, but maybe I am wrong.
Thanks for the reply,
Geoff

DesktopDave · « **Reply #3 on:** September 23, 2011, 03:54:22 PM »

The sender is just a single signal. It has an isolated "floating" ground to keep the signal clean. The cluster's coding chip has a value for the diff ratio (I'm guessing).

The cluster also sends that same signal to the cruise control module, MPG gauge and 13-button OBC if installed.

Geoff · « **Reply #4 on:** September 24, 2011, 06:29:41 AM »

no cruise control on car, mileage guage works, and OBC just has random flashing numbers all over the place...cant really make much of a determination there...my buddies OBC does the same thing in a 92 vert 318i..I may just live with it a while till I feel like tearing into the dashboard..at this rate probly next summer:rolleyes:
Thanks,
G

DesktopDave · « **Reply #5 on:** September 24, 2011, 07:30:13 AM »

My OBC does the same thing. It's not the 13-button though. A little push on the faceplate usually fixes it for me. I think it's just a loose pin on the wiring harness.

The OBC is a cinch to remove...pry off the faceplate carefully, then pinch the top & bottom retaining clips & finagle it forward & out. No need to wait for next summer!

Geoff · « **Reply #6 on:** September 24, 2011, 11:09:38 AM »

Oh, I didnt wait to fix the OBC. I've got a piece of black electrical tape on the display, fixed it right quick:o
G