Need help with fuel guage please!

OK...a 1976 PA 28 151..

After a few minutes of running, the port guage will start to fall
towards E.

It is showing 3/4 now (fuel at tabs), and will sag to 1/4 within
about 15 min, while I am operating on the starboard (other) tank.

Shut down for a few hours, guage resumes normal (correct) indication.

We have checked / replaced, tank grounds, sender, wiring to guage.

I think the guage terminals handle 12 V to the left terminal
(looking at it from under the panel) (starboard terminal) , The other
to the tank sender (port terminal).. (grounding this terminal when
the fault is present will cause a "full" indication).

From what I recall, there is a "ground" connection internal in the
guage. Anybody know how this is grounded?

I suspect a bad connection here somewhere..

Driving me up the wall..of course every time I attack the problem,
meter in hand, it works fine.

Anybody any ideas? Suggestions or test procedures?

Dave

Dave wrote:
OK...a 1976 PA 28 151..

After a few minutes of running, the port guage will start to fall
towards E.

It is showing 3/4 now (fuel at tabs), and will sag to 1/4 within
about 15 min, while I am operating on the starboard (other) tank.

Shut down for a few hours, guage resumes normal (correct) indication.

We have checked / replaced, tank grounds, sender, wiring to guage.

I think the guage terminals handle 12 V to the left terminal
(looking at it from under the panel) (starboard terminal) , The other
to the tank sender (port terminal).. (grounding this terminal when
the fault is present will cause a "full" indication).

From what I recall, there is a "ground" connection internal in the
guage. Anybody know how this is grounded?

I suspect a bad connection here somewhere..

Driving me up the wall..of course every time I attack the problem,
meter in hand, it works fine.

Anybody any ideas? Suggestions or test procedures?

Dave
Sounds like the float is filling up or becoming saturated......
Michelle

-----Original Message-----
From: Michelle ]
Posted At: Wednesday, March 01, 2006 5:52 AM
Posted To: rec.aviation.owning
Conversation: Need help with fuel guage please!
Subject: Need help with fuel guage please!

Dave wrote:
OK...a 1976 PA 28 151..

After a few minutes of running, the port guage will start to fall
towards E.

It is showing 3/4 now (fuel at tabs), and will sag to 1/4 within
about 15 min, while I am operating on the starboard (other) tank.

Shut down for a few hours, guage resumes normal (correct)
indication.

We have checked / replaced, tank grounds, sender, wiring to guage.

I think the guage terminals handle 12 V to the left terminal
(looking at it from under the panel) (starboard terminal) , The
other
to the tank sender (port terminal).. (grounding this terminal when
the fault is present will cause a "full" indication).

From what I recall, there is a "ground" connection internal in the
guage. Anybody know how this is grounded?

I suspect a bad connection here somewhere..

Driving me up the wall..of course every time I attack the problem,
meter in hand, it works fine.

Anybody any ideas? Suggestions or test procedures?

Dave
Sounds like the float is filling up or becoming saturated......
Michelle
[Jim Carter] Wouldn't that tend to move from reliable to unreliable and
then stay there or get worse? Why would shutting down tend to reset
everything if it was a float? I has to be something that is
deteriorating electrically over a period of time while the power is
applied. Then when power is removed the charges bleed down and return to
normal until the next time power is applied. I don't know the circuit
but it sure sounds like there is a capacitor somewhere that is applying
a charge to the circuit until the power is removed and the bleed
resistor does its job.

Dave writes:

OK...a 1976 PA 28 151..

After a few minutes of running, the port guage will start to fall
towards E.
....
Shut down for a few hours, guage resumes normal (correct) indication.

We have checked / replaced, tank grounds, sender, wiring to guage.

What about engine grounds? Battery grounds?


I think the guage terminals handle 12 V to the left terminal
(looking at it from under the panel) (starboard terminal) , The other
to the tank sender (port terminal).. (grounding this terminal when
the fault is present will cause a "full" indication).

From what I recall, there is a "ground" connection internal in the
guage. Anybody know how this is grounded?

I suspect a bad connection here somewhere..

Well, that's a fair guess. Especially since it looks like
the sender resistor is "0 ohms == full; many ohms == empty"...

Driving me up the wall..of course every time I attack the problem,
meter in hand, it works fine.

Tape a spare DVM under the panel, near the gauge. This threat should scare
it into working....

But let's do an obvious test. Can you swap the leads to the two
tanks; so the left shows on the right gauge and vice versa? [Assuming
such can be done legally and safely, of course -- can you placard
it or such?]

That will reduce it to gauge vs sender resistor+wiring+grounds.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

But let's do an obvious test. Can you swap the leads to the two
tanks; so the left shows on the right gauge and vice versa? [Assuming
such can be done legally and safely, of course -- can you placard
it or such?]

That will reduce it to gauge vs sender resistor+wiring+grounds.


On the Cherokee 140 you can swap the gauge/sender with a simple swap of
2 wires on a barrier strip under the rear seats. Check the Service
manual to see if there is a similar setup in the Warrior. The barrier
strip is probably behind the baggage area or under it.

Good Luck,
Mike

Mike Spera writes:


But let's do an obvious test. Can you swap the leads to the two
tanks; so the left shows on the right gauge and vice versa? [Assuming
such can be done legally and safely, of course -- can you placard
it or such?]

That will reduce it to gauge vs sender resistor+wiring+grounds.


On the Cherokee 140 you can swap the gauge/sender with a simple swap of
2 wires on a barrier strip under the rear seats. Check the Service
manual to see if there is a similar setup in the Warrior. The barrier
strip is probably behind the baggage area or under it.

That's a good first step, and if the problem moves, it's clear it's
outbound of there.

But if it does not move, you must go back and swap wires at the
gauges to be sure.

I too think it's the sender, but... many fuel gauges have a crude
voltage regulator inside, and if that is what's drifting....




--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Thanks all, but note in my post, the sender has been replaced with
new, the rsistance is exactly on spec, and no dead spots in it's
operation..

The fuel level has no effect on the fault..the guage literally "goes
to sleep" when ever it feels like it, usually after about 15 mins,
then occassionally, during flight, "wakes up" and reads correctly for
a few minutes.. then away it goes.. (down)..

Switching wires to the guages is a bear of a job under the panel, but
I may do it back under the seat, just to be sure..

Anybody know where to get a wiring diagram/component location info on
the WArrior? my CD manual is a bit lacking here...

Dave

On Thu, 2 Mar 2006 23:53:40 +0000 (UTC), David Lesher
wrote:

Mike Spera writes:


But let's do an obvious test. Can you swap the leads to the two
tanks; so the left shows on the right gauge and vice versa? [Assuming
such can be done legally and safely, of course -- can you placard
it or such?]

That will reduce it to gauge vs sender resistor+wiring+grounds.


On the Cherokee 140 you can swap the gauge/sender with a simple swap of
2 wires on a barrier strip under the rear seats. Check the Service
manual to see if there is a similar setup in the Warrior. The barrier
strip is probably behind the baggage area or under it.

That's a good first step, and if the problem moves, it's clear it's
outbound of there.

But if it does not move, you must go back and swap wires at the
gauges to be sure.

I too think it's the sender, but... many fuel gauges have a crude
voltage regulator inside, and if that is what's drifting....

Dave wrote:
: Thanks all, but note in my post, the sender has been replaced with
: new, the rsistance is exactly on spec, and no dead spots in it's
: operation..

: The fuel level has no effect on the fault..the guage literally "goes
: to sleep" when ever it feels like it, usually after about 15 mins,
: then occassionally, during flight, "wakes up" and reads correctly for
: a few minutes.. then away it goes.. (down)..

: Switching wires to the guages is a bear of a job under the panel, but
: I may do it back under the seat, just to be sure..

: Anybody know where to get a wiring diagram/component location info on
: the WArrior? my CD manual is a bit lacking here...

Some PA28's (like my mechanic's T-Arrow) have a strange sending unit setup.
IIRC, there are two per tank, and they must be *insulated* from the tank. Putting the
wrong washers on the sending unit will ground them and cause weird readings (like 1/2
full when full, etc).

I haven't followed the details of this thread, but that might be worth looking
into. Swapping wires at the disconnect under the rear seat sounds like an easy way to
check.

If you do go under the panel, I seem to remember something a bit weird about
how the gauges were wired in mine. The service manual should have the schematic all
laid out.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On Fri, 3 Mar 2006 11:56:11 +0000 (UTC),
wrote:


If you do go under the panel, I seem to remember something a bit weird about
how the gauges were wired in mine. The service manual should have the schematic all
laid out.

the main thing to remember is that the gage terminal posts are
insulated from the tray they are mounted to. if you install an
insulating washer wrong (or leave one out) and a post shorts out to
the tray, you've got serious problems.

TC