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Search for Gremlins

 
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bakerocb



Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

PostPosted: Sun Aug 17, 2008 7:49 pm    Post subject: Search for Gremlins Reply with quote

8/17/2008

To reply to the author, write to "F. Tim Yoder" <ftyoder(at)yoderbuilt.com>

Report on this weekends search for Gremlins;

I spent several hours under the panel checking all the ground buss
connections, breaker and switch grounds. I loosened the connections to the
amp, volt, oil temp and oil pressure gauges, wiggled the terminals and re
tightened. I did the same thing to the alternator and removed the regulator
spades and replaced them.I removed the radio, cleaned the connectors and re
installed it. I checked the ground straps from the engine to the motor
mount. I spent some time looking for something,anything wrong.

I started the plane and found that I had not ran off any Gremlins. When I
turn on the Alt. the oil pressure dropped from 75# to 60# then settled on
70#, this takes about one second. As soon as I turn off the Alt. the oil
pressure goes back to 75#. With the radio and Alt. on the oil pressure
needle drops a needle width when I key the radio. Again, with the Alt. off
keying the radio does not effect the oil pressure gauge which was back to
75#.

I did not fly so I didn't have any radio issues. I think I need to find the
cause of the apparent load on the oil pressure gauge first.

Oh, the Amp. meter is a little positive at idle and the voltage is showing
a charge of about 14.4V and 13.5V with at Alt. off.

I'll appreciate any suggestions.

Thanks again, Tim


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nuckolls.bob(at)cox.net
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PostPosted: Mon Aug 18, 2008 6:19 am    Post subject: Search for Gremlins Reply with quote

At 11:47 PM 8/17/2008 -0400, you wrote:
Quote:


8/17/2008

To reply to the author, write to "F. Tim Yoder" <ftyoder(at)yoderbuilt.com>

Report on this weekends search for Gremlins;

I spent several hours under the panel checking all the ground buss
connections, breaker and switch grounds. I loosened the connections to the
amp, volt, oil temp and oil pressure gauges, wiggled the terminals and re
tightened. I did the same thing to the alternator and removed the regulator
spades and replaced them.I removed the radio, cleaned the connectors and re
installed it. I checked the ground straps from the engine to the motor
mount. I spent some time looking for something,anything wrong.

There should be no ground straps from engine to motor mount. Only
one fat-wire jumper from crankcase to your single-point ground on
the firewall.
Quote:
I started the plane and found that I had not ran off any Gremlins. When I
turn on the Alt. the oil pressure dropped from 75# to 60# then settled on
70#, this takes about one second. As soon as I turn off the Alt. the oil
pressure goes back to 75#. With the radio and Alt. on the oil pressure
needle drops a needle width when I key the radio. Again, with the Alt. off
keying the radio does not effect the oil pressure gauge which was back to
75#.

I did not fly so I didn't have any radio issues. I think I need to find the
cause of the apparent load on the oil pressure gauge first.

It sounds like a ground loop issue driven by too much resistance
between crankcase and the oil pressure instrument ground. Try
removing the existing ground wire for the instrument and
grounding the instrument directly to the crankcase.

If this makes the wiggle go away, I'll suggest you remove all
jumpers from engine to mount and add one fat-jumper between
crankcase and ground block.

Quote:
Oh, the Amp. meter is a little positive at idle and the voltage is showing
a charge of about 14.4V and 13.5V with at Alt. off.

Those numbers are right in the ballpark.
Quote:
I'll appreciate any suggestions.

Thanks again, Tim

Bob . . .

----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------


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ftyoder(at)yoderbuilt.com
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PostPosted: Mon Aug 18, 2008 8:52 pm    Post subject: Search for Gremlins Reply with quote

Hello Bob,

Thank you for your suggestions. I will try grounding the oil pressure gauge
directly to the engine case and report the results.

FYI, my plane is a KIS two place all composite that I have been flying for
about 10 yrs. She has a little over 300 hrs. on her. This is a new problem
.As far as I know .I didn't add or change any operating systems prior to
these symptoms showing up.

Thank You Again, Tim

---


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ftyoder(at)yoderbuilt.com
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PostPosted: Tue Aug 19, 2008 12:26 pm    Post subject: Search for Gremlins Reply with quote

Hello Bob,

I did as you suggested and ran a temporary ground wire from the oil pressure
inst. to the crankcase. THE WIGGLE WENT AWAY!

I'll remove the engine to engine mount jumpers and add a fat ground wire
from the grounding buss to the crankcase per your recommendation.

Your time and effort, like O.C. Baker's, sure saves a lot of us a ton of
time and money.

Many Thanks, Tim
---


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PostPosted: Tue Aug 19, 2008 5:11 pm    Post subject: Search for Gremlins Reply with quote

At 09:41 PM 8/18/2008 -0700, you wrote:

<ftyoder(at)yoderbuilt.com>

Hello Bob,

Thank you for your suggestions. I will try grounding the oil pressure gauge
directly to the engine case and report the results.

FYI, my plane is a KIS two place all composite that I have been flying for
about 10 yrs. She has a little over 300 hrs. on her. This is a new problem
.As far as I know .I didn't add or change any operating systems prior to
these symptoms showing up.

Thank You Again, Tim
At 01:14 PM 8/19/2008 -0700, you wrote:
Quote:

<ftyoder(at)yoderbuilt.com>

Hello Bob,

I did as you suggested and ran a temporary ground wire from the oil pressure
inst. to the crankcase. THE WIGGLE WENT AWAY!

I'll remove the engine to engine mount jumpers and add a fat ground wire
from the grounding buss to the crankcase per your recommendation.

Your time and effort, like O.C. Baker's, sure saves a lot of us a ton of
time and money.

Many Thanks, Tim

I'm pleased that it was such a simple fix. I'm also pleased
that you brought it up here on the List! In spite of our
reverence for The Word according to ISO: (1) cleaning the
spot where a terminal goes to structure and (2)
testing with a super-duper $high$ bonding meter, there
is often too little attention paid to ground system
architecture. "Grounding" is probably one of the least
understood technologies in vehicular systems design.

It gets worse every year with new design goals by the
special interest groups. One bunch of guys worry about
power distribution. Another bunch worries about
antenna performance. Yet another worries about lightning.
Another gets paid for sifting the sands on EMC/RFI
issues. Finally, there's the structures guys who
are more worried about corrosion and do their best
to insulate the important parts that the rest of
the guys are trying to keep connected together!

Fortunately for us in OBAM aircraft land, there
are some pretty simple recipes for success that tend
to yield consistent results over thousands of
airplanes. I've tried to gather those ingredients
together in chapter 5 and keep watching for new
things to add. Your willingness to share your
experience here validates one of the recipes
and is much appreciated.

Bob . . .


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PostPosted: Sun Aug 24, 2008 10:41 pm    Post subject: Search for Gremlins Reply with quote

With the success of the test of running a new ground wire from the oil
pressure gauge to the engine case, that removed the wiggle when I activated
the Alt., I did as you suggested and ran a new fat - ground wire (8 gauge)
from the engine case to the ground block. I then removed the original engine
to motor mount jumpers and temporary oil pressure ground wire. I started the
engine and wiggle came back. DRATS! I then removed all the ground wires from
the ground block, cleaned the blocks and re installed the grounds. O/P
needle still wiggles in the same way. The only part of the system I haven't
checked is the battery which is located behind the baggage compartment, I
planed to do that this week.

If this report leads you to any other suggestions I will certainly
appreciate them.

Tim


--


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PostPosted: Mon Aug 25, 2008 4:43 am    Post subject: Search for Gremlins Reply with quote

At 11:33 PM 8/24/2008 -0700, you wrote:
Quote:

<ftyoder(at)yoderbuilt.com>

With the success of the test of running a new ground wire from the oil
pressure gauge to the engine case, that removed the wiggle when I activated
the Alt., I did as you suggested and ran a new fat - ground wire (8 gauge)
from the engine case to the ground block. I then removed the original engine
to motor mount jumpers and temporary oil pressure ground wire. I started the
engine and wiggle came back. DRATS!

8 AWG is small for the usual engine ground. I used
to fabricate custom case ground jumpers for builders
from three concentric conductors of copper braid
that added up to about an 0 AWG wire. But 8 AWG has
a resistance of just under a millohm/foot, it should
be okay. How long is the wire?

By the way, I'm not sure I recall what engine,
alternator and airplane combination we're talking about.

Quote:
I then removed all the ground wires from
the ground block, cleaned the blocks and re installed the grounds. O/P
needle still wiggles in the same way. The only part of the system I haven't
checked is the battery which is located behind the baggage compartment, I
planed to do that this week.

Where does the battery ground?

Quote:
If this report leads you to any other suggestions I will certainly
appreciate them.

If push comes to shove, you can certainly leave the
oil pressure gage grounded to the engine. The stimulus
that upsets it is on the order of tens of millivolts.
Not enough to bother other accessories in your airplane -
only those instruments where sensors get grounded to
the crankcase. It would be interesting to see what
combination of 'fixes' makes the problem go away but
let's not spend a lot of $time$ on it . . . the
exercise at this point is more academic than practical.

Bob . . .


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PostPosted: Mon Aug 25, 2008 9:36 am    Post subject: Search for Gremlins Reply with quote

Robert L. Nuckolls, III wrote:
Quote:
Where does the battery ground?

> If this report leads you to any other suggestions I will certainly
> appreciate them.

May I expand on that? Look at the automotive world ...

The most difficult job the battery has is cranking the engine. All
modern automobiles - of which I am aware, anyway - run a large ground
cable (#4 - #00) straight from the battery to the engine. The starter
motor is grounded via the engine. Then the chassis is grounded to the
engine. Everything else is grounded to the engine, via the chassis or a
ground bus.

If you want a robust electrical system, that's a good starting point.

And yeah, I've been told before "that's cars; cars aren't airplanes".
Sorry - the physics works the same for both.

Dale R.
COZY MkIV #0497
Ch.12; Ch's 13, 16, 22 & 23 in-progress


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