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Post by chrisp5b on Jun 24, 2019 19:25:29 GMT
Hello,
The tachometer of my P5b coupe shows double amount of revolution per min. Beside the wrong counts the function looks quite ok. Im just hoping that someone have a good idea what it could be.
Thanks
Chris
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Post by johnwp5bcoupe on Jun 24, 2019 20:47:14 GMT
Hi Christian, Welcome to the Forum if all is original the Tacho is probably in need of a rebuild most likely dry capacitors due to age, probably less cost to get a replacement from David Green. LINK |
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Post by djm16 on Jun 25, 2019 23:32:20 GMT
Do you have a standard ignition system?
There are two types of tachometer, the earlier ones are triggered by current pulses down the cable from ignition switch to the coil (a single turn of the cable passes around a transformer core on the back of the tach), later ones are triggered by voltage pulses (the tach is connected across each end of the ignition lead to the coil, and a current passing down this lead will create a potential difference V=IR due to the non-zero resistance of the lead).
In either case, a non-standard coil *might* allow two pulses per spark event to trigger the tachometer - one (the normal one) as the points close and a second (extra) as the points open. Both events generate a pulse current in the power cable, just that one is larger than the other.
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Post by johnwp5bcoupe on Jun 26, 2019 8:24:22 GMT
Hi Christian, if all is original the Tacho is probably in need of a rebuild most likely dry capacitors due to age |
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Post by chrisp5b on Jun 26, 2019 17:33:35 GMT
Dear all,
Thanks a lot for the nice welcome in the forum and the very valuable responses.
Even i just purchased the car view months ago and the former owner was a fun of adding meters of unneeded wires which i had to remove already, the tachometer installation seems to be originally inline with the wiring diagram between 15 supply of the injection key to the coil.
I was more hoping there is a way to adjust it but according you good explanation i will not waste time and bring it to a specialist to rework it.
Thanks
Chris
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Post by Phil Nottingham on Jun 26, 2019 17:43:56 GMT
The rear of the tacho has the wire loop then?
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