pork
Posted a lot
Posts: 1,658
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Apr 14, 2013 19:34:18 GMT
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Why would my rev counter say I'm doing more revs than I am?
It shows idle speeds ok, then when driving, it will sometimes say I'm doing 5k, then sometimes it's off the scale (when it's defiantly nowhere near that sort of speed)
Seems to do it more when I come of throttle too, say at 5k, let of pedal alltogether and it goes to 7k
Any help appreciated
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MrSpeedy
East Midlands
www.vintagediesels.co.uk
Posts: 4,786 
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Apr 14, 2013 23:44:42 GMT
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Is it driven from the coil or alternator?
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pork
Posted a lot
Posts: 1,658
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Coul
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MrSpeedy
East Midlands
www.vintagediesels.co.uk
Posts: 4,786
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Apr 15, 2013 16:48:47 GMT
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Then I'd suggest that there's a selector switch somewhere to choose between 4,6,8 etc cylinders and that it's on the wrong one
If it's not that, then I dunno!
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pork
Posted a lot
Posts: 1,658
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Apr 15, 2013 17:13:19 GMT
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Yeah it's on right one, would it be better for it to ave it's own earth? At the moment it's in a 3 gauge pod and sharing an earth cable
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MrSpeedy
East Midlands
www.vintagediesels.co.uk
Posts: 4,786
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Apr 15, 2013 17:17:10 GMT
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Depends what it's sharing it with, but seperate earths are never a bad idea. Especially with electronic items. It's counting electrical pulses, so anything that gives out interferance could affect it
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pork
Posted a lot
Posts: 1,658
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Apr 15, 2013 19:36:11 GMT
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Ok, thanks, il give it a go
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Apr 16, 2013 21:48:11 GMT
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Agree with the above - they count electrical pulses so check all mains and feed wires and give it a separate earth and see if that sorts it.
I fitted one recently and initially just bodged it in for testing and it would sometimes jump around a bit as the wires were getting jiggled about.
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v8ian
Posted a lot
Posts: 3,765
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Apr 16, 2013 22:14:43 GMT
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is it running thru a voltage stabiliser, that might be the problem alternators don't always deliver 12v.
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Atmo V8 Power . No slicks , No gas + No bits missing . Doing it in style.
Austin A35van, very different------- but still doing it in style, going to be a funmoble
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Apr 16, 2013 23:29:49 GMT
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Had a similar problem myself recently.
The problem with many 'budget' tachos currently available, is that they don't actually count the individual spark pulses. They instead work on the integrator principle - I.e. they're actually showing the cumulative charge emitted from the coil.
The big 'over-swing' when lifting off is related to the distributor advance.
Out of interest, are you running points ignition?
Since I changed to an electronic set up, my rev counter has actually settled down a lot.
This could be due to a few things - I'm guessing less back EMF from the coil, but possibly also a more regular, metered voltage and charge.
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Last Edit: Apr 16, 2013 23:30:37 GMT by misterbob
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Out of interest, are you running points ignition? Since I changed to an electronic set up, my rev counter has actually settled down a lot. This could be due to a few things - I'm guessing less back EMF from the coil, but possibly also a more regular, metered voltage and charge. Ive had a similar issue it would read about 1000rpm over and would rev to 8000rpm :-O and was erratic between times, I put it down to points and condenser but haven't changed to electronic ignition yet to prove this yet |
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