chrisf
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| posted on 25/6/06 at 05:36 PM |
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Tach feed from coils??
Hi All:
While I have the car torn to bits sorting other issues, I really need to solve my tacho problem. Right now, it only reads half the RPM. These are
stock '98 'blade clocks on a stock '98 'blade engine. The engine wiring loom was modified by Westfield. and it looks like they
pulled the tachometer feed from the ECU.
Now I cannot imagine why the ECY would spit out half the RPMs to the gauges, but it seems it does. My understanding is that it is possible to pull the
RPMs from the negative side of the coils. How do I do this? Ans is this a better solution than feeding the tacho from the ECU?
How does the 'Blade ECU get its RPM info?
--Thanks, Chris
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ruskino80
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| posted on 25/6/06 at 06:21 PM |
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not sure about hoda but a recent fzr600 i rebuilt had the tacho feed (1 wire)teed into one of the coil (of the two)feeds-but traced back this also
went to the cdi unit-connected up and it worked fine and that was with 94 clocks 92 loom and 90 cdi!
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Ferrino
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| posted on 25/6/06 at 06:35 PM |
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AIUI, if you take the RPM feed from a wasted spark coil you will get 2 'pulses' for every engine revolution, so I doubt this would work on
a bike clock (ie. don't they expect one pulse for every rev?).
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Bob C
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| posted on 25/6/06 at 10:35 PM |
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Signal from a coil lead on a wasted spark system has 1 pulse per rev. Normal coil (on a distributor) gives 2 pulses per rev on a 4pot engine. When I
worked on a ZX9R carbed engine, the ECU tacho output was 2 pulses per rev. On my homemade dash, I've so far assumed that the ECU output is 2
pulses per rev but I'm not sure yet if this is right or not (I'll have to see what the rev limiter and gear display say when I have some
road to play with). I'd be a bit worried about feeding coil voltages into a tacho that's expecting a clean logic signal from an ECU - even
the LT side of ignition coils see over 300V spikes every spark.
cheers
Bob
PS - in summary - your tacho might read 1/2 revs if it's wired to a coil instead of the ECU tacho signal - it would see 1 pulse per rev instead
of 2
[Edited on 25/6/06 by Bob C]
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chrisf
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| posted on 26/6/06 at 02:40 AM |
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I found it!
Thanks for all the replies. Looks like BobC hit the nail on the head:
quote:
in summary - your tacho might read 1/2 revs if it's wired to a coil instead of the ECU tacho signal - it would see 1 pulse per rev instead of 2
Frustrating Westfield would do that, especially since none of their diagrams show this!
--Chris
 
Rescued attachment DSCN0133.JPG
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