Tachometer unresponsive or sporadic

Talk about the E-Type Series 3

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Hembo62
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Joined: Thu Sep 16, 2021 4:33 pm
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#1 Tachometer unresponsive or sporadic

Post by Hembo62 » Thu Sep 16, 2021 4:43 pm

Hi All

New to the forum and life with an etype... Have a Series 3 2+2 that I am slowly working through.

I have an issue with my Tacho... It responds up to about 2,000 RPM, then sticks when clearly the revs have increased. If I then tap the glass, the needle will jump up to about 3,000 RPM and stick at that level and not increase, irrespective of the actual engine RPM.

Does this sound like an electrical/earth fault... Or does this issue sound like an internal tacho issue...?

Updated Comment.... The car has had Electronic Ignition added at some stage...


Thanks for any help or advice

Regards, Steve

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mgcjag
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#2 Re: Tachometer unresponsive or sporadic

Post by mgcjag » Thu Sep 16, 2021 4:50 pm

If it changes by tapping it sounds like an internal guage issue.....Steve
Steve
69 S2 2+2 (just sold) & Building a C type replica, 1960 xk150fhc

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Hembo62
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Joined: Thu Sep 16, 2021 4:33 pm
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#3 Re: Tachometer unresponsive or sporadic

Post by Hembo62 » Thu Sep 16, 2021 4:56 pm

Thanks mgcjag...

I have read some comments on the impact of Electronic Ignition on the Tacho... Is that also the same for the S3 V12...?

Would like to check out the unit in the car if possible.

Thanks, Steve

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MarekH
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#4 Re: Tachometer unresponsive or sporadic

Post by MarekH » Thu Sep 16, 2021 5:19 pm

If you pull the front off of the instrument, then you can check whether there is a mechanical reason why the needle sticks. Sporadically not working or fluttering is often a sign of a bad earth inside the unit.

kind regards
Marek

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Pete G
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#5 Re: Tachometer unresponsive or sporadic

Post by Pete G » Fri Sep 17, 2021 10:27 am

All S3 V12s came out of the factory with electronic ignition, OPUS. If you wish to ask questions relative to the ignition system you need to say which system is now fitted. The OPUS has become unreliable with age and several different after market replacements have been/are available.
Pete G(formally e-bygum)
1971 S3 2+2 OSB

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Rui
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#6 Re: Tachometer unresponsive or sporadic

Post by Rui » Thu Oct 14, 2021 5:02 pm

I had an issue with the tachometer (S3) , it behaved erratically , sometimes not at all. I have a Petronix ignition system.
I went a long way to find the reason, changing condensers etc in the tachometer to no avail. Inside there is a small IC from Texas Instruments that eventually stops working. You cannot get this IC any longer, I even contacted TI and spoke with a guy ws in the team who designed in the 70s (now retired...). I fixed it with a an external module that can be attached to the back of the tachometer. It is not very accurate, mostly at very low revs like idling but it works. I can look for the supplier if interested, it was in the UK.

Rui

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