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Jumping Needle
https://www.ausmini.com/forums/viewtopic.php?f=2&t=35622		 Page 1 of 2
Author:  1018cc [ Mon Sep 10, 2007 12:27 pm ]
Post subject:  Jumping Needle
Hey guys,

I've got a bit of a problem. I have just installed a smiths tacho into my car and everything seems to be hooked up fine (good ground, soldered connections etc). The only problem is that the needle jumps around alot. It's ok when under acceleration and shows the correct rpm (and is very smooth) but when it is under light/no acceleration the needle can jump around a bit. When I back off in 4th gear at 25mph it showed me doing 5,000rpm! It generally jumps around by 500rpm.

I've had a search and couldn't find the thread I was after but I have a feeling that I remembered reading somewhere that a similar thing happened to someone else and it was the voltage stabiliser on the way out. What do you guys think?

Cheers, Nick
Author:  brickworx [ Mon Sep 10, 2007 1:13 pm ]
Post subject: 
Maybe it needs its own power supply... not one off a split wire
otherwise it can read all pulses from anything electrical
Author:  1018cc [ Mon Sep 10, 2007 1:19 pm ]
Post subject: 
It does have its own power supply, it is directly hooked up to the fuse box. Could it be getting interferance from other electrical things. Do you think that could be causing it?
Author:  brickworx [ Mon Sep 10, 2007 1:25 pm ]
Post subject: 
That is normally the case
try a clean line straight off the ignition switch
Author:  1018cc [ Mon Sep 10, 2007 1:27 pm ]
Post subject: 
Thanks Steve, will try that when I get home.

P.s. Looks great 8) Thanks
Author:  Mick [ Mon Sep 10, 2007 1:30 pm ]
Post subject: 
Look for poor/loose connections as well. When a contact is broken, a back emf spike is produced (the spark you can often see when disconnecting things live). A loose connection will do this when it vibrates around and will upset all manner of instruments. Voltage stabiliser can do this as well internally.
Author:  brickworx [ Mon Sep 10, 2007 1:32 pm ]
Post subject: 
Tacho shouldn't run through a stabiliser as it needs 12volts supply constant
Author:  9YaTaH [ Mon Sep 10, 2007 6:53 pm ]
Post subject:  Taco Belle
New or old Tacho :?:

It could be the instruments movement...not hard to fix but a specialist job.
Author:  pristic [ Mon Sep 10, 2007 9:24 pm ]
Post subject: 
In my clubby S... with the stock tacho the needles bounce too.
If I am cruising and sitting on same speed, tacho reads beautifully... but say you shift gear and hit it, its all over... 3000rpm no 8000rpm, no, 4000rpm, no 6000rpm ah, settles on 5000rpm .... then its time to change gears!!! Start all over again.

I bought a new tacho on the weekend... Speco and its great.

Peter.

PS: Not quite sure this helps you, but at least someone else has bouncing needles :D
Author:  1018cc [ Tue Sep 11, 2007 10:57 am ]
Post subject: 
Mick wrote:
Look for poor/loose connections as well. When a contact is broken, a back emf spike is produced (the spark you can often see when disconnecting things live). A loose connection will do this when it vibrates around and will upset all manner of instruments. Voltage stabiliser can do this as well internally.


I'll go back over my signal wire and see what I can find.

9YaTaH wrote:
New or old Tacho :?:
It could be the instruments movement...not hard to fix but a specialist job.


Its a second hand one off steve (out of a rover) - so old. It shouldn't be the instruments movement because when I got it converted to positive earth I got it checked to see that it still worked ok - which it does.

pristic wrote:
I bought a new tacho on the weekend... Speco and its great.


I would have prefered a better brand of tacho but it would have looked too out of place in my car.
Author:  1018cc [ Tue Sep 11, 2007 1:35 pm ]
Post subject: 
Ok, I have taken brickworx advice on board and have hooked it up directly to the ignition. I have taken Mick's advice and pulled all my solders apart and re-soldered them with alot of solder (couldn't see any that could have been causing problems). So I think I'm just worrying about nothing. It is better than it was though but it still reads high when I get off the gas. I'll learn to live with it as it is heaps better.

Thanks for your help, Nick.
Author:  slinkey inc [ Tue Sep 11, 2007 4:58 pm ]
Post subject: 
My 1275LS tacho jumps around a lot. The faster you accelerate the slower the tacho moves, change down a gear and gun it, it bounces around like crazy. It was doing really well until recently, then it went back to this crap, which happened a while back but disappeared.

I don't care though, I can hear the engine, and can change gear when boost starts getting up. But I thought I'd ad dmy name to the 'bouncy tacho list'.
Author:  pristic [ Tue Sep 11, 2007 9:26 pm ]
Post subject: 
1018cc wrote:
pristic wrote:
I bought a new tacho on the weekend... Speco and its great.


I would have prefered a better brand of tacho but it would have looked too out of place in my car.


I have access to Autometer guages, almost a whole set but they are worth more than my mini. The Speco does the job better than the smiths one I have, I cant fault it... more than happy.
Author:  Mick [ Tue Sep 11, 2007 9:36 pm ]
Post subject: 
I split the seperate smiths tacho and dizzy issue from this post in to a new one to save confusion.

http://www.ausmini.com/forums/viewtopic.php?t=35686
Author:  albino235 [ Tue Sep 11, 2007 9:43 pm ]
Post subject: 
Hijacking yet again,

1. Wires to the dizzy;
-One red and black from the coil, red from +ve, black from -ve
-The coil also has a sense wire connected to the -ve terminal which I did have
connected to the tacho (now to nothing, I tried through the tacho and straight to
ground and nothing
-The last wire to the coil is the ignition and goes to the positive side
2. I am not sure what dizzy it is, I assume its standard just with electronic setup (the PO put it in)

I will pick up the parts to convert the dizzy back to points and see if that makes any difference, if that doesn't work ill put my thinking cap back on, or offer some beer in return for a kind soul lending me a dizzy.
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