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Re: [LML] LIVP Oil Pressure Question
(TSIO550E)...Fluctuat
Perhaps the rigged grounding wire to the engine (at one aft
outcropping) was insufficient. A solid ground to a terminal post
would be sensible.
The transducer is a "single wire standard ground" VDO
150 psi Oil pressure Sender obtained from Grand Rapids for the Chelton
EAU. It obtains its ground through the NPT threads
(supposedly).
http://usa.siemensvdo.com/products_solutions/marine/marine-instruments/ocean-line-engine-monitoring/sensors-and-senders/pressure-sender/individual-pressure-senders/Individual-Pressure-Senders.htm
0-150 PSI
1/8-27 NPT 29/12 360 00
"Please note:
VDO senders have tapered threads. DO NOT use teflon tape or pipe
sealant. This will interfere with grounding. "
It is mounted on the firewall via an insulated (rubber grommet)
Adell clamp, so no grounding through the metal sensor casing.
The engine is brand new. Not a reman.
No apparent pinpoint leaks based on a number of hours of clean
operation.
I will pursue sensor grounding as the priority issue.
Then examine the oil pressure range (30-60psi).
Appreciating everyone's input.
Jeff L
N334P
My first
suspicion would be an electrical problem with or around the oil
pressure sensor. You mentioned that you rigged a ground wire.
Depeding on how it's hooked up it may or may not affect the problem.
I've seen some engine sensors read erratically because of where the
ground lead from the engine interface box (the box all of the
engine sensors are wired to) was physically attached.
The problem may affect multiple sensors, or only one. For
example on a Legacy using a JPI engine monitor the installation manual
said to attach the ground wire from the engine interace box to the
engine block. We first tried an unused stud (it was
real convenient) on the back of the engine where the vacuum
pump would be, if it had a vacuum pump. The tach reading
jumped all over the place. We removed the ground wire from that
stud and attached it to the large ground stud running through the
firewall to the engine. The tach worked fine after that.
After thinking about it I suspect attaching the ground wire to the
vacuum pump pad created a secondary return path from the engine
back to the rest of the system that was in parallel with the primary
return path (a "ground loop").
Bad.
What type of
oil pressure sensor do you have? Is it a 4-wire sensor? A
3-wire sensor? Single wire sensor? If it's a multi-wire
sensor does its ground wire run back to the engine interface box?
If it's a single-wire sensor, and the sensor case isn't attached to
the engine, then the case of the sensor should probably have a
wire running back to the same ground as the engine interface box.
Does the installation manual specify how to ground the
sensor?
Tom
Gourley
Hello
Jeff-
A few WAGS:
Do
the connectors have a wire sleeve and are they crimped with a ratchet
crimper? I had a fluctuating EI fuel pressure gauge and the shop had
used automotive crimpers. I recrimped or replaced the connectors and
the problem went away.
Is
the engine new as opposed to reman? I bought a new replacement engine
from TCM and discovered the seat for the pressure relief was rough. It
had to be faced with a hand tool supplied by the tech rep. If it was a
reman I think the odds are against that having gone unnoticed in
previous runs.
I
have an aerobatic Continental IO-360 in my Chipmunk. When I
bought the plane the oil pressure would be stable when cold but
fluctuate erractically when hot. I did a lot of of
testing looking for a correlation to power settings, tried
adjusting the pressure relief, even changed the spring and
plunger; no good. En route to OSH the pressure dipped to 0
briefly then came back up. Quick landing, fiddle with the relief,
ground run was fine. A while later in cruise it happened again.
Landed, replaced the engine with new. On test flight, the SAME
fluctuations! Refacing the seat didn't help (see above). TCM didn't
know what to do. Turns out it was cavitation- the Christen valve and
hoses used for Lycomings (-10) is too small for the
Continental. At cruise settings there just wasn't enough oil getting
to the pump. The engine was originally used for a military
trainer down under- the manufacturer discovered they had to make
their own valve body with -16 fittings. That solved my
problem. Do the fluctuations go away at lower RPM settings? If so
there might be a restriction in the pump
supply.
The TSIO-550 Overhaul Manual shows that the pump
body is sealed with silk thread. I know nothing
about it but if there was a pinhole leak in the right
area?
I
think the mechanical gauge makes sense as a check but it's
another hole to seal for pressurization. -Bill
Wade
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