I flew today with my new piece of 12 AWG from the rectifier-regular to
earth.
It didn't make any difference that I could see !
I have one of those strange earthing faults that I will find eventually -
although a consistent reading (no matter what it is is the most important
thing).
I have been trying to determine some basic facts.
I know that if a temperature sender is disconnected the gauge reads low
scale. I know that if the temp sender wire is shorted to earth the gauge
reads high scale.
What I don't know is these two equivalent statements in the case of the oil
pressure sender. My memory when building was that something did something
strange. I think the oil pressure cable if shorted to earth gives zero
reading and if open circuit gives full scale. I THINK. I would have to take
the lower cowl off to check this. Is there anyone with their engine cowlings
open who could do the test for me ?
At present once warm and 5000 my oil pressure gauge reads 3.1 bar. This goes
up to 4 bar when the engine is idling (!!!!!!). There are a number of
possibilities
1. The oil pressure ACTUALLY goes up at idle
2. That lower volts at idle gives a higher reading
3. A poor earth somewhere is causing a a connection back through another
instrument.
Originally in the cruise the oil pressure would be 3.1 or 4 bar, and would
change back and forth at 5 or 10 minute intervals, and the two temp gauges
would move in unison. This implied an earthing problem, so I connected up a
special uncut cable directly from the earth bus for the instruments to the
engine block. I was expecting this to stabilise the fluctuations, which it
did, but I was expecting it to stabilise at the higher reading - and it
didn't - it stabilised at the lower reading!
With the open circuit and shorted details for the oil pressure sender I
might be able to work out the logic ! Maybe !
I will also try connecting my special earth cable to the case of the
regulator rather than the engine block.
TIA
Richard
Richard F.W. Holder 01279 842804 (POTS)
Bell House, Bell Lane, 01279 842942 (fax)
Widford, Ware, Herts, 07860 367423 (mobile)
SG12 8SH email : rholder@avnet.co.uk
Europa Classic Tri-gear : G-OWWW, High Cross
PA-28-181 : Piper Archer : G-JANA, EGSG (Stapleford)
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