[V8] Tempermental tach and warning light/chime

[urq]

With all you describe it almost has to be the instrument cluster internal
connection issues.  The engine will not run with the speed sensor failing
... not that the speed signal has any direct effect on the tach.  If the
speed sensor was the source of the tach dropping, the engine would be
stopping or losing power too.  

When you hear the oil pressure warning chime what is the pressure gauge
reading?  You said you changed the sender ... that drives the gauge.
There's a separate switch for the warning chime.  

I don't remember if there's a write up on the KB ... doesn't matter as the
KB is down anyway ... but disassembling the IC is not very complicated ...
there are a bunch of screws around the back cover of the IC ... remove them
and the back comes off ... with some circuit boards attached.  You'll see a
bunch of metal posts that are the interconnects between the boards, and
several ribbon cable interconnects.  Get some DeoxIt or similar (I recommend
the spray ... you can get it at Radio Shack) and apply it to the
interconnections you see.  Since you're having tach issues, make sure you
find the pins for the tach and ensure they are well treated.  Disconnect the
ribbon cable connectors and spray the pins on the headers.  Put everything
back together the way it came apart and cross your fingers!  You may want to
wait to put the dash cover back on until you have verified that the IC is
working again ... in any case it really isn't that tough to get the IC out
... 

HTH!
Steve B
San José, CA (USA)

-----Original Message-----

Another question for the pros....

My other V8 (1990 with auto and 175 000 miles) has a tempermental tachometer
and oil pressure warning light/chime.  I guess that I need to know whether
I'm likely dealing with the infamous instrument cluster problem that plagues
some V8's or something else.  The car runs well, period.  The tachometer
sometimes works.  While driving it can alternate between being operational
and inoperational without the car missing a beat.....this problem began
about 3-6 months ago and seems to becoming more frequent.  The oil pressure
warning light/chime has been an intermittent problem now for over a year and
may be worsening.  It chirps up frequently.  I have swapped the oil pressure
sender with no effect.

Would the car run if the rpm flywheel sensor was failing?  Should I replace
that?...or is that a red herring?

If this problem is by far most likely related to the contacts in the
instrument cluster, does anyone have access to a write-up on how to tackle
this problem so that I can make swift and error-free repairs?......knowing
step-by-step how to dismantle the dashboard would be a big plus....

.....still loving the machines and hanging onto them despite being tempted
by newer metal....it's amazing how resistant V8's are to corrosion.