[urq] tach failure

[Brandon Rogers]

And I bet your wife is _much_ better than me at electrical stuff!
Seriously.

Thanks for the great input, Steve.

Brandon

----- Original Message ----- 
From: "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>
To: "Urq List" <urq at audifans.com>
Sent: Thursday, October 07, 2004 10:53 AM
Subject: RE: [urq] tach failure


... my wife and I frustrate each other from time to time because
whenever there is an electrical connection problem on something she says
it must be "shorting" ... I try to explain to her that a "short" is a
very specific condition, one that in fact is rare in situations like
this ... and for many reasons is good that it is rare.  Sorry about the
rant ... I would say the situation would probably be better described as
an "opening" ... ;-)

You've got some sort of electrical connection problem going on.  A tach
is a very simple device in terms of its interface, it gets power, ground
and the tach signal from the coil.  If the tach quits working the
problem is a connection issue on one of these inputs or the tach itself
is bad.  Given that you seem to be experiencing other electrical issues,
I'd guess that the tach is OK.  Unfortunately, most electrical
connection problems are intermittent, and so the process of opening up
the area to investigate may fix the problem.  Fortunately, on the urq
you can get access to the IC without having to move it much ... pull the
cover off, but leave the IC in place and attached.  Start the engine and
see if the tach is working.  If it is you might want to try wiggling the
wires a bit to see if you can't make it fail.  Assuming you can make it
fail, measure power and ground at the tach to see if one or the other is
missing.  You can check for the tach pulses with an external tachometer
...

Before I dig in too far on a troubleshooting session like this the first
thing I do is to collect the information about the various odd behaviors
and look at the related circuits in the wiring diagram to see if there
are any common threads.  I would recommend that you do this.  Be as
specific as you can in terms of the observations you've made ... and
also see if you can repeat  them ...

Recently I've had a couple instrument cluster issues that turned out to
be connection problems in the flexible circuit board that provides the
wiring for the instrument panel.  Unfortunately it is very difficult to
identify hairline fractures and such.  I think this is probably where
your time will be best spent ...

Steve B
San Jose, CA (USA)
Perhaps I should start calling myself West Coast Steve?  ;-)
>
> Occasionally my tach just dies.  Sometimes I would start the
> car and have no tach and re-start would solve it.   Sometimes
> I'd be tach-less for a couple weeks then one day it would
> come back.  Now I've noticed that on the rare occasion I honk
> the horn, the tach can die.  Ditto headlights...or is it
> brights.....can't remember.
>
> Seems like it's shorting???
>
> So I plan to get inside the IC (not the intercooler) this
> weekend...what do I look for (besides a new tach!)????
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