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lindbergh
11-02-2013, 06:59 PM
My tach indicates 1500 when I turn off the engine. With the ignition on it works normally indicating 0 before starting and valid engine RPM when running. Any ideas why this is and any solutions? Thanks.
thirdmanj
11-02-2013, 07:14 PM
My tach indicates 1500 when I turn off the engine. With the ignition on it works normally indicating 0 before starting and valid engine RPM when running. Any ideas why this is and any solutions? Thanks.

Sounds pretty "tachy" to me....

Mine does this too. To my knowledge lots of others are this way, it's a design thing.
DMCMW Dave
11-02-2013, 08:01 PM
They all do this.
LordFly
11-03-2013, 01:32 AM
It's a DeLorean thing :) But the value they "rest" at seems to be different. I've seen mine stop as high as 4500 before. The good news is, when the engine is running, they do what they're supposed to.
DMCVegas
11-03-2013, 01:34 AM
It's an awesome feature. If you get pulled over just point to the tach and tell the officer that you had no idea how fast you were going because your speedometer was broken. Just look at the stuck needle!
WelmoedJ
11-03-2013, 04:31 AM
Up top now I haven't seen a D with a tacho needle at zero RPM with ignition off.
That only happens with ignition on and no running engine.
Mine halts at 2900 RPM.

I presume it's in the electronics of the RPM system that causes this peculiar behavior.
Perhaps one of the Dave's has a technical explanation for this phenomenon?
Elvis
11-03-2013, 05:00 AM
It's the chip that is designed this way !

LM1819

am I the only one wasting his time with taking stuff like this apart and reading datasheets
instead of guessing ?
thirdmanj
11-03-2013, 06:58 AM
It's the chip that is designed this way !

LM1819

am I the only one wasting his time with taking stuff like this apart and reading datasheets
instead of guessing ?

Yup...

I'm not sure why anyone else bothered to comment after Dave posted. Figured that was pretty much the answer right there. Either way, does it really matter? Seems pretty trivial.
Rich
11-03-2013, 11:55 AM
They all do this.

Dave's right.

The same tachometer "off mode reads high" behavior is found in late C3 ('75-'82) Corvettes, perhaps other GM cars of that vintage.

Your local concours judge may question it and casual onlookers will likely think the tach is broken.

As I recall the D's instruments were sourced from GM.
David T
11-03-2013, 01:56 PM
In LotusSpeaK TADT ,,, SIR! (They All Do That) There is even an emoticon for it on the Forum! As they say now it is not a design flaw, IT IS A FEATURE!
thirdmanj
11-03-2013, 03:09 PM
In LotusSpeaK TADT ,,, SIR! (They All Do That) There is even an emoticon for it on the Forum! As they say now it is not a design flaw, IT IS A FEATURE!

David T has spoken.

:lockdance: this b-tch. ;)
kings1527
11-03-2013, 05:54 PM
David T has spoken.

:lockdance: this b-tch. ;)

Ha! Seriously!
dustybarn
11-03-2013, 06:16 PM
The old adage is, "AC lies and DC dies". A DC instrument (such as the oil pressure gauge) will typically drop to zero on power-off, whereas an AC instrument like the tach will hang where it is or indicate a spurious reading. Nothing to worry about.