I just spoke with Lycoming regarding my very high fuel flow. Recently
I've had a problem where I'm getting almost double my normal fuel flow
at idle even with the mixture at the edge of cut-off. I suspected a
servo but called Lycoming. They said I may have a nozzel with a
blockage and the other nozzles are streaming because of it.
Does this make any sense? Could a blockage cause an *INCREASE* in fuel
flow?
I have a JPI fuel transducor wheel that measures fuel flow that has
shown to be very accurate.

-Robert

I'd do a flow test then clean all injectors and do another flow test. Just
have some help and extinguishers around as already mentioned.

Get your hands on 4 baby food jars with lids.
Poke 3 holes in each lid, center large hole for the injector nozzle, 2
outside holes for a piece of stiff wire to fashion into a hanger. (and to
vent air)
Weigh each empty set up, record empty weights.
Insert nozzles into center holes, screw jar onto cover.
Run boost pump after your helpers have been awakened and armed with
extinguishers.
Weigh each jar, compare net fuel weights.
Clean, lather, rinse, repeat.
Jim

Sounds like they didn't understand that you are observing the high fuel flow
on an in-line true flowmeter rather than their pressure-based panel meter.


"Robert M. Gary" > wrote in message
ps.com...
>I just spoke with Lycoming regarding my very high fuel flow. Recently
> I've had a problem where I'm getting almost double my normal fuel flow
> at idle even with the mixture at the edge of cut-off. I suspected a
> servo but called Lycoming. They said I may have a nozzel with a
> blockage and the other nozzles are streaming because of it.
> Does this make any sense? Could a blockage cause an *INCREASE* in fuel
> flow?
> I have a JPI fuel transducor wheel that measures fuel flow that has
> shown to be very accurate.
>
> -Robert
>

Stan Prevost wrote:
> Sounds like they didn't understand that you are observing the high fuel flow
> on an in-line true flowmeter rather than their pressure-based panel meter.

That's what I thought but I reenforced what I was saying several times.
I really just don't want to send a 600 hr fuel servo for O/H for $2K if
it doesn't need it.

-Robert

Robert M. Gary wrote:
> I just spoke with Lycoming regarding my very high fuel flow. Recently
> I've had a problem where I'm getting almost double my normal fuel flow
> at idle even with the mixture at the edge of cut-off. I suspected a
> servo but called Lycoming. They said I may have a nozzel with a
> blockage and the other nozzles are streaming because of it.
> Does this make any sense? Could a blockage cause an *INCREASE* in fuel
> flow?

I remember discussing this when working on my A&P, and promptly forgot
about it after I got out of school. IIRC, it has something to do with
the fuel injection...if one is blocked, the other nozzles pick up the
loss and are sometimes too efficent.

Obviously I can't remember the exact cause, but I've heard the same
exact thing before...blockage can cause an increase in fuel flow.

Why don't you just have the nozzles cleaned and rule that out?

Robert M. Gary wrote:
> Stan Prevost wrote:
>
>>Sounds like they didn't understand that you are observing the high fuel flow
>>on an in-line true flowmeter rather than their pressure-based panel meter.
>
>
> That's what I thought but I reenforced what I was saying several times.
> I really just don't want to send a 600 hr fuel servo for O/H for $2K if
> it doesn't need it.
>
> -Robert
>

This is just at idle?
Are your manifold pressure and rpm readings in line with each other?
I am thinking about cam shaft wear.

John

Robert M. Gary wrote:
> I just spoke with Lycoming regarding my very high fuel flow. Recently
> I've had a problem where I'm getting almost double my normal fuel flow
> at idle even with the mixture at the edge of cut-off. I suspected a
> servo but called Lycoming. They said I may have a nozzel with a
> blockage and the other nozzles are streaming because of it.
> Does this make any sense? Could a blockage cause an *INCREASE* in fuel
> flow?
> I have a JPI fuel transducor wheel that measures fuel flow that has
> shown to be very accurate.
>
> -Robert
>

The Visitor wrote:
> This is just at idle?
> Are your manifold pressure and rpm readings in line with each other?
> I am thinking about cam shaft wear.

Anytime. However, it is a little bit intermitent. Sometimes it "clears"
itself.
I can't increase throttle w/o increasing mixture but I *MUST* keep the
two perfectly in line, if either gets in front of the other the engine
dies. It really feels like there is no fuel regulation.

-Robert

Robert M. Gary wrote:
> The Visitor wrote:
>> This is just at idle?
>> Are your manifold pressure and rpm readings in line with each other?
>> I am thinking about cam shaft wear.
>
> Anytime. However, it is a little bit intermitent. Sometimes it "clears"
> itself.

Probably the blockage in a fuel nozzle moving around.

Robert, does it matter whether the boost pump is on or not?


"Robert M. Gary" > wrote in message
ps.com...
>I just spoke with Lycoming regarding my very high fuel flow. Recently
> I've had a problem where I'm getting almost double my normal fuel flow
> at idle even with the mixture at the edge of cut-off. I suspected a
> servo but called Lycoming. They said I may have a nozzel with a
> blockage and the other nozzles are streaming because of it.
> Does this make any sense? Could a blockage cause an *INCREASE* in fuel
> flow?
> I have a JPI fuel transducor wheel that measures fuel flow that has
> shown to be very accurate.
>
> -Robert
>

Stan Prevost wrote:
> Robert, does it matter whether the boost pump is on or not?

No, pressure holds solid at 22lbs.

-Robert

I was wondering if the excessive fuel flow indication changes with pump on
vs off.


"Robert M. Gary" > wrote in message
oups.com...
>
> Stan Prevost wrote:
>> Robert, does it matter whether the boost pump is on or not?
>
> No, pressure holds solid at 22lbs.
>
> -Robert
>

Your turbine JPI device may only report to the JPI display.
The fuel pressure indicator/fuel flow that was original
equipment shows high pressure is there is a blockage and low
fuel flow. But the higher indicated pressure is also
interpreted as a higher fuel flow.

If you have EGT on each cylinder, checking temperatures and
thus fuel being burned can help determine if the cylinders
are rich or lean.



"Robert M. Gary" > wrote in message
ps.com...
|I just spoke with Lycoming regarding my very high fuel
flow. Recently
| I've had a problem where I'm getting almost double my
normal fuel flow
| at idle even with the mixture at the edge of cut-off. I
suspected a
| servo but called Lycoming. They said I may have a nozzel
with a
| blockage and the other nozzles are streaming because of
it.
| Does this make any sense? Could a blockage cause an
*INCREASE* in fuel
| flow?
| I have a JPI fuel transducor wheel that measures fuel flow
that has
| shown to be very accurate.
|
| -Robert
|

>"Emily" wrote in message > Obviously I can't remember the exact cause, but
I've heard the same
> exact thing before...blockage can cause an increase in fuel flow.

It causes an increase in the indication on the OEM indicator which in
actuality is a pressure guage, not a flowmeter. Mr. Gary's system uses a
true flowmeter and a clogged injector line should show a decrease in flow.

D.

I don't think so, at least not very much decrease. I think the fuel will
divide among the functioning injector nozzles. This is why the pressure
increases when one is blocked, the fuel is forced through a fewer number of
orifices, causing a greater pressure drop across them.


"Capt.Doug" > wrote in message
...
> >"Emily" wrote in message > Obviously I can't remember the exact cause,
> >but
> I've heard the same
>> exact thing before...blockage can cause an increase in fuel flow.
>
> It causes an increase in the indication on the OEM indicator which in
> actuality is a pressure guage, not a flowmeter. Mr. Gary's system uses a
> true flowmeter and a clogged injector line should show a decrease in flow.
>
> D.
>
>

>"Stan Prevost" wrote in message
> I don't think so, at least not very much decrease. I think the fuel will
> divide among the functioning injector nozzles. This is why the pressure
> increases when one is blocked, the fuel is forced through a fewer number
of
> orifices, causing a greater pressure drop across them.

If we are talking about the OEM 'flowmeter', how many transducers does it
have? It would need two to measure a pressure drop. It needs only one to
measure the pressure near the spider. If it has only one transducer near the
spider, and a nozzle clogs, the remaining nozzles won't flow enough to
relieve the increased pressure and the result will be an increased 'flow'
indication.

D.

Stan Prevost wrote:
> I don't think so, at least not very much decrease. I think the fuel will
> divide among the functioning injector nozzles. This is why the pressure
> increases when one is blocked, the fuel is forced through a fewer number of
> orifices, causing a greater pressure drop across them.

But there is noticable change in pressure, just in flow. The flow is
very high. I could see that if 1 nozzle was plugged that the other 3
would have increased flow but I can't see that the total amount of fuel
delivered would be double. Fuel flow is measured by a spinning wheel
and is not pressure related.

-Robert

Capt.Doug wrote:
> >"Stan Prevost" wrote in message
> > I don't think so, at least not very much decrease. I think the fuel will
> > divide among the functioning injector nozzles. This is why the pressure
> > increases when one is blocked, the fuel is forced through a fewer number
> of
> > orifices, causing a greater pressure drop across them.
>
> If we are talking about the OEM 'flowmeter', how many transducers does it
> have? It would need two to measure a pressure drop. It needs only one to
> measure the pressure near the spider. If it has only one transducer near the
> spider, and a nozzle clogs, the remaining nozzles won't flow enough to
> relieve the increased pressure and the result will be an increased 'flow'
> indication.

The fuel flow measurement does not take into account pressure. Its just
an inline wheel that spins around.

-Robert

The pressure drop across the nozzle orifice is the absolute pressure into
the nozzle less the absolute pressure in the manifold. I don't have a
system diagram here, but I believe the factory fuel flow gauge is a
differential pressure gauge referenced to manifold pressure.

"Capt.Doug" > wrote in message
...
> >"Stan Prevost" wrote in message
>> I don't think so, at least not very much decrease. I think the fuel will
>> divide among the functioning injector nozzles. This is why the pressure
>> increases when one is blocked, the fuel is forced through a fewer number
> of
>> orifices, causing a greater pressure drop across them.
>
> If we are talking about the OEM 'flowmeter', how many transducers does it
> have? It would need two to measure a pressure drop. It needs only one to
> measure the pressure near the spider. If it has only one transducer near
> the
> spider, and a nozzle clogs, the remaining nozzles won't flow enough to
> relieve the increased pressure and the result will be an increased 'flow'
> indication.
>

But I believe they flow all the metered fuel (or nearly all of it) as long
as the fuel pump provides sufficient pressure. Do you think the fuel flow
out of the fuel injector body (fuel servo) decreases if one nozzle clogs?
Once there is enough restriction to flow so that the "back pressure" from
the spider approaches the fuel pump pressure, then flow will reduce, but
until then, I think the servo maintains the flow it wants.

"Robert M. Gary" > wrote in message
ups.com...
>
> Stan Prevost wrote:
>> I don't think so, at least not very much decrease. I think the fuel will
>> divide among the functioning injector nozzles. This is why the pressure
>> increases when one is blocked, the fuel is forced through a fewer number
>> of
>> orifices, causing a greater pressure drop across them.
>
> But there is noticable change in pressure, just in flow. The flow is
> very high. I could see that if 1 nozzle was plugged that the other 3
> would have increased flow but I can't see that the total amount of fuel
> delivered would be double. Fuel flow is measured by a spinning wheel
> and is not pressure related.
>

I assume you meant that there is *no* noticeable change in pressure. But
I'm not sure we are talking about the same thing. You measured fuel
pressure out of the fuel pump and found that it doesn't change. My question
was whether the "flow" indicated by the pressure-based factory flowmeter
changes. This is related to fuel pressure after the fuel servo, which is
not the fuel pressure you measured, I don't think. If the indication of the
factory fuel flow gauge, actuated by fuel in the fuel distribution lines,
has not changed, but the true flowmeter indication has greatly changed, then
I think you have one of two problems: The true flowmeter is broke, or you
are spewing fuel out of the system somewhere before the fuel servo, or in
it. But since the high fuel flow indication is accompanied by poor engine
performance, I think it is fuel spewing inside the servo.

If I remember right, one thing that can happen in a fuel servo is that an
internal problem can cause fuel to spew out of one of the ram air sensing
ports in the venturi, and get sucked up into the manifold, making the
mixture way too rich. The nozzles might have reasonably correct flow, but
the total flow will be too much. If this is happening, you can see blue
fuel stains in the venturi section, and maybe dripping fuel. Also you would
experience high true fuel flow. And ye$, thi$ doe$ call for overhaul of the
$ervo.

Stan

Stan Prevost wrote:
> "Robert M. Gary" > wrote in message
> ups.com...
> I assume you meant that there is *no* noticeable change in pressure. But
> I'm not sure we are talking about the same thing. You measured fuel
> pressure out of the fuel pump and found that it doesn't change. My question
> was whether the "flow" indicated by the pressure-based factory flowmeter
> changes.

I don't have a pressure-based flow indicator.

-Robert

"Robert M. Gary" > wrote in message
ups.com...
>
> Stan Prevost wrote:
>> "Robert M. Gary" > wrote in message
>> ups.com...
>> I assume you meant that there is *no* noticeable change in pressure. But
>> I'm not sure we are talking about the same thing. You measured fuel
>> pressure out of the fuel pump and found that it doesn't change. My
>> question
>> was whether the "flow" indicated by the pressure-based factory flowmeter
>> changes.
>
> I don't have a pressure-based flow indicator.
>

Oh. Sorry for the confusion. You said you had a JPI fuel flow transducer,
so I assumed that was an add-on sensor operating with an add-on instrument
and that the original factory "flow" indicator was still present. I was
assuming a certified aircraft, and you might be talking about an
experimental.

Still, a measurement of fuel pressure at the spider would be a useful clue,
as would an inspection of the venturi for fuel stains.

Stan

Stan Prevost wrote:
> "Robert M. Gary" > wrote in message
> ups.com...
> Oh. Sorry for the confusion. You said you had a JPI fuel flow transducer,
> so I assumed that was an add-on sensor operating with an add-on instrument
> and that the original factory "flow" indicator was still present. I was
> assuming a certified aircraft, and you might be talking about an
> experimental.

No, Mooney just never installed any type of flow indicator. The only
thing Mooney gave us is pump pressure. It usually drops slightly at
high power vs. low power but almost too little to notice. From my
previous Bonaza flying I understand what you are talking about though.

-Robert