PA28-181 Fuel pressure drop off - Inspired by the Gascolotor thread.

Roy Page wrote:
: Well that is what I wrote Cory, but I deleted it before sending my post :-)

: Roy

Petition the FAA to put out an AD requiring fuel system upgrades to all
PA28's?

Oh wait... bad idea....


--

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

Well you gave me a smile with that one Cory
This weekend I am going to rip out the Piper pump and put a Chevy Corvette
one in.
Yes ? .... :-)

Roy

wrote in message
...
Roy Page wrote:
: Well that is what I wrote Cory, but I deleted it before sending my post
:-)

: Roy

Petition the FAA to put out an AD requiring fuel system upgrades to all
PA28's?

Oh wait... bad idea....


--

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

"Roy Page" wrote in message
nk.net...
I bought our Piper Archer [PA28-181] just over a year ago from a
Californian owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that we
still had all the important bits still hanging on, we failed to notice
that the gascolator had a slight fuel leak until a few days after we got
the bird home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns to
mid scale in level cruise.

I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?

Roy
N5804F

Here's one...

The pressure transducer in your airplane may not have a large enough vent
port, which causes a false low fuel pressure reading when you climb and a
false high pressure reading as you descend. The transducer vents to ambient
air, so it can compare the internal (fuel) pressure to the ambient
(reference) conditions and arrive at the difference. That difference is
"fuel pressure".

If the vent port on the transducer is undersized (and they ARE small), or if
it is partially clogged, its reference pressure is off. If you're climbing,
the transducer thinks the reference pressure is higher it than it actually
is, because the higher pressure air inside the transducer's reference side
hasn't equalized to ambient. Therefore, it compares the internal (fuel)
pressure with the reference pressure and sees a smaller difference than
expected. That plays out as a low fuel pressure reading. When you descend
after being at altitude, the reference pressure is low (because you were at
a higher altitude where the air pressure is lower), and the transducer
compares the actual pressure with a low reference number, and, volia - high
fuel pressure reading.

I saw the same thing in 300 hours of flying my Tomahawk, and see it again in
my RV-6.

KB

Well Kyle that is a pretty convincing explanation.
I will take a another look at the service manual and follow your arguments
for myself.
If you are correct, and I am not doubting you, I am on my way to solving the
problem.

Thanks again

Roy

"Kyle Boatright" wrote in message
...

"Roy Page" wrote in message
nk.net...
I bought our Piper Archer [PA28-181] just over a year ago from a
Californian owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that
we still had all the important bits still hanging on, we failed to notice
that the gascolator had a slight fuel leak until a few days after we got
the bird home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns to
mid scale in level cruise.

I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?

Roy
N5804F

Here's one...

The pressure transducer in your airplane may not have a large enough vent
port, which causes a false low fuel pressure reading when you climb and a
false high pressure reading as you descend. The transducer vents to
ambient air, so it can compare the internal (fuel) pressure to the ambient
(reference) conditions and arrive at the difference. That difference is
"fuel pressure".

If the vent port on the transducer is undersized (and they ARE small), or
if it is partially clogged, its reference pressure is off. If you're
climbing, the transducer thinks the reference pressure is higher it than
it actually is, because the higher pressure air inside the transducer's
reference side hasn't equalized to ambient. Therefore, it compares the
internal (fuel) pressure with the reference pressure and sees a smaller
difference than expected. That plays out as a low fuel pressure reading.
When you descend after being at altitude, the reference pressure is low
(because you were at a higher altitude where the air pressure is lower),
and the transducer compares the actual pressure with a low reference
number, and, volia - high fuel pressure reading.

I saw the same thing in 300 hours of flying my Tomahawk, and see it again
in my RV-6.

KB

I have seen the pressure problem on two different models years of
Seminole as well.
Michelle

Kyle Boatright wrote:

"Roy Page" wrote in message
ink.net...


I bought our Piper Archer [PA28-181] just over a year ago from a
Californian owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that we
still had all the important bits still hanging on, we failed to notice
that the gascolator had a slight fuel leak until a few days after we got
the bird home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns to
mid scale in level cruise.

I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?

Roy
N5804F



Here's one...

The pressure transducer in your airplane may not have a large enough vent
port, which causes a false low fuel pressure reading when you climb and a
false high pressure reading as you descend. The transducer vents to ambient
air, so it can compare the internal (fuel) pressure to the ambient
(reference) conditions and arrive at the difference. That difference is
"fuel pressure".

If the vent port on the transducer is undersized (and they ARE small), or if
it is partially clogged, its reference pressure is off. If you're climbing,
the transducer thinks the reference pressure is higher it than it actually
is, because the higher pressure air inside the transducer's reference side
hasn't equalized to ambient. Therefore, it compares the internal (fuel)
pressure with the reference pressure and sees a smaller difference than
expected. That plays out as a low fuel pressure reading. When you descend
after being at altitude, the reference pressure is low (because you were at
a higher altitude where the air pressure is lower), and the transducer
compares the actual pressure with a low reference number, and, volia - high
fuel pressure reading.

I saw the same thing in 300 hours of flying my Tomahawk, and see it again in
my RV-6.

KB

("Roy Page" wrote)
I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?


Any way you can sneak ...a Taylorcraft(!!) into the rotation? :-)

Looked through your club's site - interesting history: Anyone propose as a
fun member's project - restoring a $12K Taylorcraft?

www.taylorcraftflyingclub.org


Montblack

Roy Page wrote:

I bought our Piper Archer [PA28-181] just over a year ago from a Californian
owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that we
still had all the important bits still hanging on, we failed to notice that
the gascolator had a slight fuel leak until a few days after we got the bird
home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns to
mid scale in level cruise.

Ideas please ?

I had lowish and fluctuating fuel pressure in an Arrow.
Turning on the electic fuel-boost pump would improve the pressure
and reduce the fluctuations.
Resealing the gascolator improved it a bit, but I was still worried.
Was considering replacing the engine-driven fuel-pump when my LAME
discovered that the the fuel-line out of the gascolator to the
electric boost pump had a crack.
He replaced that section of line and fuel pressure is now much more
into the green range with less fluctuations.

It has been a long term goal to once again have a TCraft in our fleet.
We have looked at several, but most folks want a lot of cash for a machine
that needs a "body off" restoration.
Thanks for your interest.

Roy

"Montblack" wrote in message
...
("Roy Page" wrote)
I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?


Any way you can sneak ...a Taylorcraft(!!) into the rotation? :-)

Looked through your club's site - interesting history: Anyone propose as a
fun member's project - restoring a $12K Taylorcraft?

www.taylorcraftflyingclub.org


Montblack

I watched this carefully in out PA 28-151 today...

In "enroute" climb, (83 Knts) , with the elect pump off, fuel
pressure would drop 30% down from the indication with elect fuel pump
on.

Seemed to be related to the pitch attitude,....... nose up = fuel
tanks lower related to pumps/carb.

Would make sense...

Was always in the green, engine ran fine...

Dave


On Wed, 28 Sep 2005 01:06:28 GMT, Michelle P
wrote:

I have seen the pressure problem on two different models years of
Seminole as well.
Michelle

Kyle Boatright wrote:

"Roy Page" wrote in message
link.net...


I bought our Piper Archer [PA28-181] just over a year ago from a
Californian owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that we
still had all the important bits still hanging on, we failed to notice
that the gascolator had a slight fuel leak until a few days after we got
the bird home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns to
mid scale in level cruise.

I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?

Roy
N5804F



Here's one...

The pressure transducer in your airplane may not have a large enough vent
port, which causes a false low fuel pressure reading when you climb and a
false high pressure reading as you descend. The transducer vents to ambient
air, so it can compare the internal (fuel) pressure to the ambient
(reference) conditions and arrive at the difference. That difference is
"fuel pressure".

If the vent port on the transducer is undersized (and they ARE small), or if
it is partially clogged, its reference pressure is off. If you're climbing,
the transducer thinks the reference pressure is higher it than it actually
is, because the higher pressure air inside the transducer's reference side
hasn't equalized to ambient. Therefore, it compares the internal (fuel)
pressure with the reference pressure and sees a smaller difference than
expected. That plays out as a low fuel pressure reading. When you descend
after being at altitude, the reference pressure is low (because you were at
a higher altitude where the air pressure is lower), and the transducer
compares the actual pressure with a low reference number, and, volia - high
fuel pressure reading.

I saw the same thing in 300 hours of flying my Tomahawk, and see it again in
my RV-6.

KB

Dave,
Thanks for your input to this discussion.
Your findings are almost identical to mine in my PA28-181.
I think that your comments are valid but would indicate that the mechanical
fuel pump on all PA28's is marginal.
A previous explanation of the pressure drop centered on the pressure
transducer not venting sufficiently in climb.
A situation is emerging in this discussion which clearly shows that many
PA28's exhibit this fall in fuel pressure.
Apparently without causing any fuel starvation to the engine.
Whilst a number of people have identified causes, no one as yet as come up
with a fix.
It seems that I had better take Cory's advice and cover up the gauge :-)
Thanks again.

Roy
Archer N5804F



"Dave" wrote in message
...
I watched this carefully in out PA 28-151 today...

In "enroute" climb, (83 Knts) , with the elect pump off, fuel
pressure would drop 30% down from the indication with elect fuel pump
on.

Seemed to be related to the pitch attitude,....... nose up = fuel
tanks lower related to pumps/carb.

Would make sense...

Was always in the green, engine ran fine...

Dave


On Wed, 28 Sep 2005 01:06:28 GMT, Michelle P
wrote:

I have seen the pressure problem on two different models years of
Seminole as well.
Michelle

Kyle Boatright wrote:

"Roy Page" wrote in
message
hlink.net...


I bought our Piper Archer [PA28-181] just over a year ago from a
Californian owner and flew it home to it's new base in Ohio.
On the flight home, we noticed on long climbs that the fuel pressure
fell
off from an indicated mid scale reading to about one third scale.
In level cruise the indicated pressure returned to mid scale.
Although we took the top cowl off at every stop to check carefully that
we
still had all the important bits still hanging on, we failed to notice
that the gascolator had a slight fuel leak until a few days after we got
the bird home.
You need to remove the lower cowl to get access to the gascolator.
Our A&P put a new bowl seal on the gascolator which cured the leak and
appeared to cure the fuel pressure changes.
A few months passed and then occasionally I noticed a slight fall off in
fuel pressure when climbing.
I concluded that the mechanical engine driven fuel pump must be getting
tired and, to be safe, replaced it with a new pump three weeks ago.
No change, the fuel pressure still falls off when climbing and returns
to
mid scale in level cruise.

I also belong to the Taylorcraft Flying Club
www.taylorcraftflyingclub.org.
The club, these days, flies a fleet of three PA28's.
Our PA28-180 has a similar fall off in fuel pressure when climbing.

Ideas please ?

Roy
N5804F



Here's one...

The pressure transducer in your airplane may not have a large enough vent
port, which causes a false low fuel pressure reading when you climb and a
false high pressure reading as you descend. The transducer vents to
ambient
air, so it can compare the internal (fuel) pressure to the ambient
(reference) conditions and arrive at the difference. That difference is
"fuel pressure".

If the vent port on the transducer is undersized (and they ARE small), or
if
it is partially clogged, its reference pressure is off. If you're
climbing,
the transducer thinks the reference pressure is higher it than it
actually
is, because the higher pressure air inside the transducer's reference
side
hasn't equalized to ambient. Therefore, it compares the internal (fuel)
pressure with the reference pressure and sees a smaller difference than
expected. That plays out as a low fuel pressure reading. When you
descend
after being at altitude, the reference pressure is low (because you were
at
a higher altitude where the air pressure is lower), and the transducer
compares the actual pressure with a low reference number, and, volia -
high
fuel pressure reading.

I saw the same thing in 300 hours of flying my Tomahawk, and see it again
in
my RV-6.

KB