Donners90
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 posted on 27/1/06 at 09:30 AM |
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Jumpy Speedo
I am using an ETB electronic speedo with two magnets on the prop. The speedo is set up to count pulses corresponding to the wheel size & diff
ratio. However, when stationary, it registers a speed, sometimes juming up to aound 30-40mph. When driving it appears to give a reasonably steady and
accurate reading.
I guess the jumping around could be noise from the electrical system, so is there either something I can fit in-line to remove the noise (voltage
regulator or the like) or can/should I re-wire the power feeds and earths?
Any help much appreciated
Cheers
James
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muzchap
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| posted on 27/1/06 at 10:02 AM |
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Hi mate - probably don't want to hear this... but I'd re-cable using shielded twisted pair. This should help eliminate any interference
:-)
It's dead cheap - around £1.50 metre from any good store. If you get stuck, give me a shout I know a bloke who supplies it.
Cheers,
Murray
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donut
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| posted on 27/1/06 at 10:06 AM |
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ooooh i need some of that stuff.
Can you sort me some in exchange for beer tokens?
Andy
When I die, I want to go peacefully like my Grandfather did, in his sleep -- not screaming, like the passengers in his car.
http://www.flickr.com/photos/andywest1/
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jambojeef
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| posted on 27/1/06 at 10:10 AM |
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I would imagine that the jumping is the magnets coinciding randomly with the edge of the sensors field when stationary and flickering between on and
off hence giving the wrong reading.
So if it is this its gonna be a bit tricky to solve unless you perhaps wire up a switch inline with the handbrake to de-couple the sensor?!
Eurgh!
Well its a thought anway!
Geoff
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David Jenkins
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| posted on 27/1/06 at 10:43 AM |
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You could try an 0.1uF capacitor across the wires at the speedo head - that should kill any stray pulses, without screwing up the intentional ones!
Any non-electrolytic type should do the job - polystyrene is probably the most durable.
If you don't understand a word of what I just said, seek help! 
David
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stevebubs
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| posted on 27/1/06 at 10:55 AM |
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That doesn't sound normal - my ETB registers 0 when stationary.
Have you run the speedo wires anywhere near any part of the ignition or EFi (if using) circuits? If so, reroute...
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Bluemoon
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| posted on 27/1/06 at 11:14 AM |
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Quick check to see what it is: Can you remove the sensor conection on the back of the gauge? I guess it should read zero then, if it does you know
it's the wirring/sensor...
[Edited on 27/1/06 by Bluemoon]
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gregf27
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| posted on 27/1/06 at 03:46 PM |
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Hi James,
I had a similar problem with my ETB speedo. turned out that one of the two magnets had dropped off the prop flange, so it was replaced , and the
sensor had also moved a tiny bit further away from the magnets, so I adjusted that back and its been great since, worth a try first
regards, Greg,
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stevebubs
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| posted on 27/1/06 at 04:14 PM |
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quote:
Originally posted by gregf27
Hi James,
I had a similar problem with my ETB speedo. turned out that one of the two magnets had dropped off the prop flange, so it was replaced , and the
sensor had also moved a tiny bit further away from the magnets, so I adjusted that back and its been great since, worth a try first
regards, Greg,
That would more likely cause fluctuations on the move - and was something I also suffered from when I first installed it.
Problems here are when the car is stationary so either
a) a signal is being induced into the speedo wiring from an external signal
b) the speedo is f@#cked.
Quick check is to power the speedo without anything else on the loom powered up (or just the engine off). If it reads a nice clean "0"
then you've probably got a signal being induced. If it fluctuates with nothing else running then it's likely to need to go back to ETB for
"fettling"
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Donners90
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| posted on 28/1/06 at 06:45 AM |
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Thanks for the replies guys. There looks to be a few things I can try. I won't be able to look at it 'till next weekend but I'll let
you know what cures it.
Cheers
James
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Donners90
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| posted on 7/2/06 at 10:04 PM |
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Sorted
On closer inspection, the wires from the sensor ran along side the main loom, passing the power feed from the alternator.
Ended up using a small diameter coax cable connected with BNC fittings. Speedo now works perfectly.
Many thanks for then ideas & tips
Cheers
James
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jimmyjoebob
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| posted on 7/2/06 at 11:58 PM |
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This is probably irrelevent as your speedo parts are new, but I had an audi with an electronic speedo that used to flicker. It was a specific design
fault on one of the PCBs in the dashboard - Audi fitted some devices onto pins that are only secured with solder and this cracks over time. The
solution? A firm slap to the top of the dash above the offending article. It worked too as I found to my advantage when I sold the car!
If at first you don't succeed, hide all evidence you ever tried!
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jimmyjoebob
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| posted on 8/2/06 at 12:01 AM |
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D'oh! I should have read all the postings before adding something!
Glad you found the problem - wiring makes my blood run cold!
If at first you don't succeed, hide all evidence you ever tried!
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