Fuel servo problem???

Today I went out to my plane to fly and found a very odd problem. When
I started the plane after taxiing over the fuel, I could only get it to
run when the mixture was just at the edge of idle cut off. Moving it
even 1/8 forward caused the engine to die right away.
I did some diagnostics. At 1500 RPM I was getting 22lbs of fuel
pressure (normal) and 5GPH in fuel flow (very high). As I moved the
mixture about 1/8 forward that jumped to about 6GPH until the engine
started to die. Running at 2000RPM moving the mixture control to 1/4
caused the engine to totally die.
I run the engine like this for about 20 minutes to make sure it was hot
but no improvement. I even stalled it several times (by moving the
mixture to 1/4 rich) and restarted it. Each restart required 2 seconds
of fuel boost so I don't think it was flooded.
On one restart it ran totally fine, and I was getting about 3.0 GPH at
1500 at 1/4 mixture and about 3.8GPH at 2000 RPM at full rich. So I
shut down again and tried it again and it was having the problem again,
running about 5GPH at 1500 RPM with mixture at the edge of cut-off.

The only thing I can think if is it would be a fuel servo issue. It
seems a little bit intermitant but I seem to be able to make it happen
often enough. Sadly, I'm not at the airport where I normally have
maintenance done and I don't want to fly it now. I've been told to
expect approx $3000 to OH the fuel servo. This is for an IO-360-A3B6
engine.

-Robert

Do you have an EGT on each cylinder? Do all the cylinders
run at the same temperature?

Most fuel flow gauges actually measure pressure and are
calibrated for know orifice sizes and fuel density. A
plugged fuel spider line or nozzle or a nozzle that is too
big will cause problems.

Does the engine run rough at any time before it dies?

If there is a mechanic who can help you, you can run some
time fuel flow tests by placing containers on the engine and
putting the fuel injectors in the containers ( clean
painters can could be hung under the cylinders ) and run the
boost pump for a few seconds, then measure the amount of
fuel delivered. Repeat the test with just the fuel lines if
necessary. Do this outside and have two fire guard with
extinguishers ready. You can also check the fuel pump
pressure directly.

I would not fly the airplane in that condition, either see
the maintenance people on that airport or pay your favorite
mechanic to come to you.


You might contact the factory for advise. You also might be
able to rent or borrow parts to get the plane flown to a
repair facility of your choice.


--
James H. Macklin
ATP,CFI,A&P

"Robert M. Gary" wrote in message
ups.com...
| Today I went out to my plane to fly and found a very odd
problem. When
| I started the plane after taxiing over the fuel, I could
only get it to
| run when the mixture was just at the edge of idle cut off.
Moving it
| even 1/8 forward caused the engine to die right away.
| I did some diagnostics. At 1500 RPM I was getting 22lbs of
fuel
| pressure (normal) and 5GPH in fuel flow (very high). As I
moved the
| mixture about 1/8 forward that jumped to about 6GPH until
the engine
| started to die. Running at 2000RPM moving the mixture
control to 1/4
| caused the engine to totally die.
| I run the engine like this for about 20 minutes to make
sure it was hot
| but no improvement. I even stalled it several times (by
moving the
| mixture to 1/4 rich) and restarted it. Each restart
required 2 seconds
| of fuel boost so I don't think it was flooded.
| On one restart it ran totally fine, and I was getting
about 3.0 GPH at
| 1500 at 1/4 mixture and about 3.8GPH at 2000 RPM at full
rich. So I
| shut down again and tried it again and it was having the
problem again,
| running about 5GPH at 1500 RPM with mixture at the edge of
cut-off.
|
| The only thing I can think if is it would be a fuel servo
issue. It
| seems a little bit intermitant but I seem to be able to
make it happen
| often enough. Sadly, I'm not at the airport where I
normally have
| maintenance done and I don't want to fly it now. I've been
told to
| expect approx $3000 to OH the fuel servo. This is for an
IO-360-A3B6
| engine.
|
| -Robert
|

We replaced our fuel servo on our '79 Mooney 201 in June at annual time.
They (Money Service Center) told us that the fuel servos last around
1000 hours and then need to be rebuilt. You can tell if it is time
becasue the adjustment screw will be just about out of adjustment.

We were in a hurry for our servo so replaced ours with a rebuilt unit
instead of having ours rebuilt. The cost was around 1.9 AMU's and a
couple hours labor. No where near the 3.0 AMU's you were quoted.

I think if you wanted to send yours out for rebuild it would be around
1.5 AMU's and this includes the lines and spider.

Jon Kraus
'79 Mooney 201
4443H @ UMP

Robert M. Gary wrote:
Today I went out to my plane to fly and found a very odd problem. When
I started the plane after taxiing over the fuel, I could only get it to
run when the mixture was just at the edge of idle cut off. Moving it
even 1/8 forward caused the engine to die right away.
I did some diagnostics. At 1500 RPM I was getting 22lbs of fuel
pressure (normal) and 5GPH in fuel flow (very high). As I moved the
mixture about 1/8 forward that jumped to about 6GPH until the engine
started to die. Running at 2000RPM moving the mixture control to 1/4
caused the engine to totally die.
I run the engine like this for about 20 minutes to make sure it was hot
but no improvement. I even stalled it several times (by moving the
mixture to 1/4 rich) and restarted it. Each restart required 2 seconds
of fuel boost so I don't think it was flooded.
On one restart it ran totally fine, and I was getting about 3.0 GPH at
1500 at 1/4 mixture and about 3.8GPH at 2000 RPM at full rich. So I
shut down again and tried it again and it was having the problem again,
running about 5GPH at 1500 RPM with mixture at the edge of cut-off.

The only thing I can think if is it would be a fuel servo issue. It
seems a little bit intermitant but I seem to be able to make it happen
often enough. Sadly, I'm not at the airport where I normally have
maintenance done and I don't want to fly it now. I've been told to
expect approx $3000 to OH the fuel servo. This is for an IO-360-A3B6
engine.

-Robert

Jim Macklin wrote:
Do you have an EGT on each cylinder? Do all the cylinders
run at the same temperature?

Most fuel flow gauges actually measure pressure and are
calibrated for know orifice sizes and fuel density. A
plugged fuel spider line or nozzle or a nozzle that is too
big will cause problems.

Fuel pressure stayed around 22lbs. Flow is measured by a transducer
spinning wheel ala JPI. Adding that was the best buy I ever made.

What would have happened if this happened in flight?

-Robert

You'd get busy finding a nice place to land.


"Robert M. Gary" wrote in message
ups.com...
| Jim Macklin wrote:
| Do you have an EGT on each cylinder? Do all the
cylinders
| run at the same temperature?
|
| Most fuel flow gauges actually measure pressure and are
| calibrated for know orifice sizes and fuel density. A
| plugged fuel spider line or nozzle or a nozzle that is
too
| big will cause problems.
|
| Fuel pressure stayed around 22lbs. Flow is measured by a
transducer
| spinning wheel ala JPI. Adding that was the best buy I
ever made.
|
| What would have happened if this happened in flight?
|
| -Robert
|