vindicator
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| posted on 29/8/07 at 08:31 AM |
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spiking rev counter reading
Help, got 18 hrs to sort out a rev counter problem before 2nd SVA.
After the engine is warm and the cooling fan is running the rev counter needle jumps up and down from 1000 or 2000 revs and will not become steady for
the engine speed.
The gauge has green (live 12 volt), black (earth), blue (neg coil terminal), red/white (illumination) wires. Normal 2lt pinto engine injection,
cooling fan power taken from a fuzed point from the battery.
I can't see why there should be fluctuating spikes from the coil (assuming it is the coil)....if all fails it will take 5 mins to take out the
rev counter at the sva centre.
Any help or advice greatful received.....
TimR
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nitram38
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| posted on 29/8/07 at 08:40 AM |
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A rev counter is not an sva requirement but is handy. They will have their own clip on device for the emmissions so don't worry if yours
doesn't work.
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nib1980
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| posted on 29/8/07 at 08:42 AM |
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can you not just temporarily disconnect the radiator fan for the SVA test?
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locoboy
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| posted on 29/8/07 at 08:43 AM |
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Rev counter is not required for SVA.
They take the revs from a clip on thingy that is attached to the emissions tester.
Fast idle test would kill the engine if the rad fan was disconnected.
[Edited on 29/8/07 by locoboy]
Doh,
Need to type faster then Nitram 
[Edited on 29/8/07 by locoboy]
ATB
Locoboy
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rayward
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| posted on 29/8/07 at 08:48 AM |
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are you using the stanard dizzy? with the electronice module, if so there is a dedicated tacho output from the module
Ray
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vindicator
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| posted on 29/8/07 at 08:51 AM |
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During the first SVA after the engine had warmed up, the rev counter was all over the place and as I had linked the 12 volt supply between the rev
counter and the speed o, this was affected as well. So a fail was placed on the speed o as a steady reading could not be obtained.
Now that I have separated the 12 volt supply to the speed o, this is working fine. It is just the rev counter that needs sorting out. If I do
disconect the wire from the coil and the rev counter is not working, I thought that this would be a fail....that is why I'll take the dial
out...
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vindicator
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| posted on 29/8/07 at 08:54 AM |
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Yes using the standard dizzy and I have the ECU (iv 1987) but don't know which pin number to use on the ECU to link to the rev counter....
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BenB
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| posted on 29/8/07 at 08:55 AM |
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Try attaching an earth direct from the battery to the rev counter dial or using a screened cable for the signal to the rev counter. This may all be
intererfernce...
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RazMan
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| posted on 29/8/07 at 09:42 AM |
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I would bet that you need to use a screened cable for the rev counter signal wire.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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tks
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| posted on 29/8/07 at 03:19 PM |
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yeah looks like a earth problem to the rev counter.
The above comments are always meant to be from the above persons perspective.
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vindicator
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| posted on 29/8/07 at 08:00 PM |
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thanks for the advice...but I can't see why it can be an earth problem when the engine is cold or warming up the rev counter works spot on. It
is only when the electric fan comes on for a few mins that indicates that normal engine temp has been reach and then the rev counter gets the
jitters....
Can some one educate me if you still think it is a earth problem....
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RazMan
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| posted on 29/8/07 at 08:10 PM |
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The signal line is probably picking up interference from the fan motor and shielding (earthing) the signal line should stablise the input.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Macbeast
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| posted on 29/8/07 at 08:56 PM |
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Or - the current taken by the fan motor may be enough to put a ripple on the 12V supply line.
Are your clocks fed from a decent (ie semiconductor) regulator ?
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