rogim46

I'm trying everything I can to figure out why the speedometer and tachometer are not working on my 1985 (early) Porsche 944.


I can start the car and the MPG area on the tachometer works as I step on the accelerator. The first gauge also appears to be working (fuel, temp, etc). When I took out the gauges, I can shake the speedometer/tachometer and needles move freely. They just don't move when I press on the accelerator.



I already replaced speed/reference sensors and cleaned (most) grounds I could find.

I took apart the console to see what is going on there and found these wires not connected.



































Could any of these wires be related to speedometer/tachometer not working?



What/where else should I be checking? Could the speedometer/tachometer be bad? Are they connected in a way in which if one does not work, the other stops working? Would a bad O2 sensor prevent the speedometer/tachometer moving?


I also have this relay sitting deep in dash, apparently not connected to anything. Anyone know what it could be for?

Tiger03447

Most of these wires look they go to a radio...the one with the inline fuse is for a power source..the big round black one is an antenna lead, presumeably going out to the left front fender...not sure about the little white two pronger though...one or two should go through the LF fender out to the antenna motor..power leads...What color wires does the WSM say about the speedo and tach..and how they are wired. Have you checked all the instrument fuses? may be more than one...:>)) ! thanks, tiger 03447

kens_74911s

Early cars Speedo and tach share connections. Use to be wiring diagrams at texasblake.com. I think Pelican has some also. I have them if you get in a bind.
I just picked up a complete set of gauges with connectors I could break up if you need something.
K

rogim46

I'm not sure what to do with the wiring diagrams. Can I diagnose a bad tachometer/speedometer using them, or will it only tell me the signals they receive?

kens_74911s

The schematics will assure you everything is connected properly.
Seems some of the loose wires you selected go to the center console that looks to be pulled back. Climate fan, gauges oil psi/Volts /Clock & illumination etc.
K

benjj

The early cars run the speedo and mileage reading from the speedo cable. It is not powered, it's mechanical. It links from the back of the speedo via a square metal adapter to the front left wheel hub.

You've probably just got a broken speedo cable. A new one costs peanuts and easy to replace.

rogim46

I took the dust cap off, that is connected to speedo cable. As I spin it, I see it spinning at the dash. Could this still give me bad speedometer readings/data, even if it spins freely?

Currently, I got the speedometer gauge to oscillate around the 20 mph mark. The tachometer RPM gauge still does nothing. as shown in this video


https://docs.google.com/file/d/0B6MJ...N4YWcwSGV3aTA/


When I release the accelerator, my car almost stalls, then kicks back to normal. If anyone knows how to diagnose this, let me know. I'll probably make a separate post for this issue.

kens_74911s

Look here :
http://forums.pelicanparts.com/porsc...ncey-tach.html

Tiger03447

Dear Rogim: According to some other posts, I've read, just this AM, the stalling issue is due to the early DME..not an issue if the car is running...welcome to the world of early 944's...later one's don't do this apparently...thanks, Tiger 03447