Fuel Pump Clue requested

[Tim Hickey]

I have a Zenith CH-300 with a Lyc 0-320. It has an engine mounted fuel
pump, and an electric aux pump. I also have a fuel pressure gauge, and
a low fuel pressure warning light. Today, for the first time, when I
did my pre-flight run-up, the low fuel pressure light came on. When I
looked at the fuel pressure gauge, I was showing 2 pounds, or maybe
just a touch less. When I turned on the boost pump, the pressure went
right back up to 6 pounds or so.
In flight, with the boost pump off, the pressure shows about 3 or 4
psi. That is with partial throttle, and an rpm of maybe 2300 to 2400.
If I go to full throttle, the pressure will drop to around 2 psi, and
the low fuel pressure light will come on. The engine never gives any
indication of being starved for fuel. But something is changing. The
key question I have here, is how do fuel pumps wear out. Is a
reduction in delivered pressure or volume symptomatic of the pump
nearing the end of it's service life? Or maybe we have a partially
blocked check valve that is leaking a bit? Does the spring inside get
weak with time?
And, one last question, where is a good (reasonable price) source for
a pump? I have looked at Trade-A-Plane, and sticker shock is still in
effect.

Thanks.

Zenith CH-300 Driver.

[[email protected]]

Hope you can solve your problem. If not you may consider another way
out. I use two electric Facet fuel pumps in my bird and no mechanical
pump. 125 hrs so far and no problems with the fuel pumps for the 200HP
Franklin engine. Have dual batteries - one pump on each.
--------------------------------------------
http://www.abri.com/sq2000

[Denny]

My first suspicion is that you have a pin hole in the diaphragm...
Pull the pump apart and inspect... Order parts and repair yourself...
denny

[DonMorrisey]

Hi Tim.

You may want to consider signing up for this email group on lycoming
engines, even temporarily and ask your question:
http://groups.yahoo.com/group/lycoming/

There are some very knowledgeable people on this list. Actually if you
sign up, search the archives, I know your problem has been mentioned in
the past.

Good luck. Don.

[Tim Hickey]

Thanks, Don, Good advice. I will

And Denny,
If I had a pin hole, would I not have a leak somewhere?
And the big question, where can I get replacement parts?

Thanks.


On 15 Dec 2006 09:54:57 -0800, "DonMorrisey" >
wrote:

>
>Hi Tim.
>
>You may want to consider signing up for this email group on lycoming
>engines, even temporarily and ask your question:
>http://groups.yahoo.com/group/lycoming/
>
>There are some very knowledgeable people on this list. Actually if you
>sign up, search the archives, I know your problem has been mentioned in
>the past.
>
>Good luck. Don.
>

Zenith CH-300 Driver.

[Denny]

Not necessarily... The leak can be contained and yet the pressure will
be down...
There are other possibilities: worn eccentric on the cam, worn plunger
rod, bad spring on the regulator, etc... But if it had been fine and
suddenly the pressure turned up low it is likely something sudden such
as a cracked diaphragm...
Parts can be had from a number of repair shops and or vendors.. Look in
Trade-A-Plane... Check on Sacramento Air Ranch, as one source of
parts...
The first thing is to pull the pump and have someone who speaks
homebuilt aircraft help you inspect it... Usually something will be
apparent...

denny

Tim Hickey wrote:
> Thanks, Don, Good advice. I will

[Tim Hickey]

Thanks Denny, Having built the machine from plans, I do speak
hombuilt.
And I agree with your list of potential problems.
However, I will send you a beer if you can point me to a vendor who
will sell me a new diaphram for the pump. I sure have not been able to
find one. Do you think there might be an automotive diaphragm that
would work?
At this point, my money is on the inlet check valve leaking.
Sometimes. At shut down, the pump seems to hold pressure between
itself and the carb.
I hate to replace the pump not knowing that it is the problem, but I
am running out of ideas.

Thanks
Tim.


On 18 Dec 2006 08:33:20 -0800, "Denny" > wrote:

>Not necessarily... The leak can be contained and yet the pressure will
>be down...
>There are other possibilities: worn eccentric on the cam, worn plunger
>rod, bad spring on the regulator, etc... But if it had been fine and
>suddenly the pressure turned up low it is likely something sudden such
>as a cracked diaphragm...
>Parts can be had from a number of repair shops and or vendors.. Look in
>Trade-A-Plane... Check on Sacramento Air Ranch, as one source of
>parts...
>The first thing is to pull the pump and have someone who speaks
>homebuilt aircraft help you inspect it... Usually something will be
>apparent...
>
>denny
>
>Tim Hickey wrote:
>> Thanks, Don, Good advice. I will
>

Zenith CH-300 Driver.

[Orval Fairbairn]

In article >,
(Tim Hickey) wrote:

> Thanks Denny, Having built the machine from plans, I do speak
> hombuilt.
> And I agree with your list of potential problems.
> However, I will send you a beer if you can point me to a vendor who
> will sell me a new diaphram for the pump. I sure have not been able to
> find one. Do you think there might be an automotive diaphragm that
> would work?
> At this point, my money is on the inlet check valve leaking.
> Sometimes. At shut down, the pump seems to hold pressure between
> itself and the carb.
> I hate to replace the pump not knowing that it is the problem, but I
> am running out of ideas.
>
> Thanks
> Tim.

Bad news. IIRC, diaphragm-type fuel pumps are NOT rebuildable!
Apparently, FAA thinks that there is too much opportunity for failure in
rebuilt pumps of this type. Also, automotive diaphragms are thinner than
those in aircraft pumps.

If your check valve is leaking, you just MIGHT be able to substitute a
new automotive valve.



> On 18 Dec 2006 08:33:20 -0800, "Denny" > wrote:
>
> >Not necessarily... The leak can be contained and yet the pressure will
> >be down...
> >There are other possibilities: worn eccentric on the cam, worn plunger
> >rod, bad spring on the regulator, etc... But if it had been fine and
> >suddenly the pressure turned up low it is likely something sudden such
> >as a cracked diaphragm...
> >Parts can be had from a number of repair shops and or vendors.. Look in
> >Trade-A-Plane... Check on Sacramento Air Ranch, as one source of
> >parts...
> >The first thing is to pull the pump and have someone who speaks
> >homebuilt aircraft help you inspect it... Usually something will be
> >apparent...
> >
> >denny
> >
> >Tim Hickey wrote:
> >> Thanks, Don, Good advice. I will
> >
>
> Zenith CH-300 Driver.

[[email protected]]

A leaking diaphragm will often allow fuel into the crankcase and
the oil level will rise, smell like fuel and get really thin.
More likely it's a faulty check valve, or if the engine is one
that's flown for short flights, the spring in the pump has corroded and
broken, reducing the output pressure. The spring is on the crankcase
side of the diaphragm and the corrosive moisture and blowby gases can
attack it. If this is the case, the magnetos should be looked at as
well. Their impulse couplngs can corrode and their springs might break,
retarding the timing to around zero BTDC and lowering power to some
useless level. A real danger with the Bendix dual magneto used on some
Lycs. Both mags are driven by the one gear and coupling.

Dan