Electronic autometer speedo goes wild after short drive
 

Does anybody have an idea what to do or look after. I have a electronic speedometer from autometer with my T56 and it really works fine until 15-20 minutes drive.Needle bounces all over like crazy! Some time it stays on 0 and then goes full sweep back and fort.

Check your ground on the sending unit wire coming from the trans.

If you do have good continuity to ground, then it looks like there's a good possibility that you have a simple calibration issue with the unit itself.

I'd then suggest you contact Autometer.

Thank you Theresa!!! Okay i check the ground first. That has come to my mind too. But i dont think its the calibration,because it works like a dream first 10 miles.

I did email to autometer tech.They just said ; take the power lead of from the alternator and see what happens. I have asked around and nobody suggest to diconnect that wire off. I am afraid it could toast the ecm ?

A few questions before I can troubleshoot:
Are you using a 3 wire or 2 wire sender?
And how do you have the wires hooked up?

If you'd rather us try to help you over the phone, it might be quicker since there will be a few "try this"; "try thats" going back and forth.

Hello Theresa,thank you for your help!! I ll find out the answers of your questions. If its okay , i rather talk to you via email or this because of time difference, i am from Finland , so when you guys are sleeping we are wrenching;)

Okay. You can contact us here. :thumbsup:

We supply the wiring for a lot of their products, so if this is an issue with the wiring, I'll be able to help you. But if the issue is with the actual Autometer unit itself, I'll still have to refer to back to Autometer because I can't really troubleshoot for them.

Theresa,ill give you mail soon!! And i had to say we are lucky to have you here:thumbsup:

This sounds very much like a signal interference problem (due to electrical noise). I had a similar problem with an Autometer speedo on my '67. The eventual solution was to run separate power and ground leads to the sender and speedo, and to tightly twist power, ground, and sender wires together. It worked ...

Call Autometer, mine did the same thing and they warrantied it, told me they had a bunch of them that were bad like that. I think I have seen my new one do the same thing though in the limited time I drove the car

Might even try a shielded twisted pair on the sensing leads guys and ground one end of the shield. The amount of electrical noise in today's ignitions and control systems could easily overwhelm low voltage sensing inputs. I'm actually amazed there isn't more shielding protection required in all these low voltage systems and components when it comes to interface wiring. And the frequency these computers, digital gages, and entertainment systems operate at also can cause noise or false signal interference when not grounded or shielded properly.