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From: (no name) (no email)
Date: Thu Aug 11 2005 - 00:33:00 EDT
Quoting Mark and Beth Mowery <>:
> Hi,
>
> My diesel tach is 3 years old, and recently it's been showing erratic rpm
> readings when the engine is running at a constant fuel setting>
............... snip foir brevity <<<<<<<<<<<<<<<<<
> does this most likely indicate a tach problem, or is it
> actually possible that I have the beginning stages of a malfunctioning
> injector that the tach is picking up on?
>
> Mark Mowery
> Owosso, MI
REPLY
Piezo-electric transducers like tiny tach uses are high impedance devices.
Presumably the lead from the transducer to tach readout is shielded.
Look for things like corroded conenctions, broken shield connections and cracks
in the outer cable sheath.
Also consider if new electrical equipment has recently been added which might
be introducing stray magnetic fields which will inductively couple into the
tach lines.
I recently had a similar problem with an Aeettna tach wwhich suddenly would not
read properly. Turns out ta mechanic working on the water pump had broken a
wier and "fixed" it by runnign a new wier by a different route back to the
dash. In effect he had the negative wier going back along the starboard side
oof the engien and the positive wire along the port side of the engine block.
Evidently this mass of ireon innssside the "loop" of the wirea caused a loss
of signal strenght. Running new twin conductors in parallel from transducer to
sender fixed the problem.
Finally keep in mind that peizo -electric transduceres do age and if not made
to strinfgent quality standards do degrade over time resulting in lower signal
output.
Only a qualified diesel injection test bench would prove if there is any loss
of injection pessure presaging a future failuer.
Go with the easier and less expensive allternatives first when trouble shooting.
regards
Arild
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