I have a stock 911T 2,2 from 1971.
My tach is working fine the first 30 seconds when the car is cold. Suddenly it goes down, and will just twitch/jump once in a while.
First i thought it was my contact points in the distributor that needed adjustment, so I did. I bougth new contacts, adjusted them 0,40mm (we use the metric system here
), and I adjusted the timing all perfect (The distributor is Magneti Marelli).
No luck with my tach though.
Here's what I did next:
1. Tested for + and ground in the back of the tach. No problems there.
2. Cleaned all the connections behind the tach, on the distributor and in the speed switch (the black/purple wire between tach and distributor is looped to the speed switch to make fuel cut off).
3. I checked for connection in the black/purple wire. No problems there.
4. I have a small stock of spare parts, so I found 3 other tachs that I tried in the car. That didn't work. I have never tried them in my car before so I don't know if they even work.
5. When that didn't work, I had to be sure there was nothing wrong with the black/purple wire, so I made a new one directly from distributor to tach. Still the same problem.
Now I don't know what to do. I would like to test my 4 tachs in some way, and I would like to messure something on the signal from the distributor.
Can anyone give me a hint, how I:
- Test the rpm signal on the distributor?
- Bench test my tachs?
Any other ideas/hints? Have I misset anything?
Please don't post that NHspeedo can fix my tach. I know. They are going to fix it as soon as I know that the fault is in the tach.
Thanks (and sorry for my English skills)