Odd starting problem

Perhaps somebody here has an idea about this little problem.

A few weeks ago, shortly after annual, I tried to start our Cherokee 140.
It kicked for a few revs, and then failed to start no matter what I did.
I noticed the aux fuel pump kept pumping, as if it was not building
pressure. The primer seemed to have fuel. I noticed fuel on the carpet
and leaking outside below the aux pump. We had our mechanic replace the
aux pump gasket a few days later. I then flew the plane twice after that
without any problems.

So today (a gorgeous day, by the way), my partner and I are going to fly.
We try to start the plane and it kicks once, then fails to start. We try
more primer. We try flooded procedures. Eventually the plane is cranking
slowly due to weakened battery. We get the car over and jump the plane.
We try everything. There is no fuel leak anywhere. There is no smell of
fuel anywhere. Aux fuel pump keeps clicking as if pressure is not being
built up, but no leaks. Primer feels like it is pumping fuel into
cylinders. Sumping fuel reveals no water. We try switching tanks. Once
the first kick happened, NOTHING would get it to fire.

So we're planning a long XC in a couple of weeks. I'm concerned that even
if our mechanic does something, we might still not have it fixed and then
we could get stuck at some podunk airport. Although I thought the problem
had been fixed previously, the symptoms are the same, minus apparent fuel
leaks anywhere.

It acts like it's not getting fuel. The fact that the initial crank fired
suggests it's not electrical. But the fact that the primer feels like
it's pumping fuel means it should fire after priming, at least for a bit.

Anybody have good ideas?

Thanks in advance.

This is EXACTLY what happens if the engine ingested water. When I
replaced my induction scat tubing, this started to happen. Seems that
the old tubing had a couple of small holes in it, one was on the bottom.
During a heavy rain, water was getting into the tubing via small cracks
in the cowling. Upon starting, the engine would fire up and immediately
shut down. All 8 plugs were full of water an no amount of cranking will
clear them. With the old tubing, the water drained off. The new tubing
held it in.

Did the mechanic replace the scat tubing at annual? When it happens
again, pull a plug. If there is water, you have a lead. If there is gas,
you flooded it. If neither, there indeed may be a fuel flow problem.

Good Luck,
Mike

Prime wrote:
Perhaps somebody here has an idea about this little problem.

A few weeks ago, shortly after annual, I tried to start our Cherokee 140.
It kicked for a few revs, and then failed to start no matter what I did.
I noticed the aux fuel pump kept pumping, as if it was not building
pressure. The primer seemed to have fuel. I noticed fuel on the carpet
and leaking outside below the aux pump. We had our mechanic replace the
aux pump gasket a few days later. I then flew the plane twice after that
without any problems.

So today (a gorgeous day, by the way), my partner and I are going to fly.
We try to start the plane and it kicks once, then fails to start. We try
more primer. We try flooded procedures. Eventually the plane is cranking
slowly due to weakened battery. We get the car over and jump the plane.
We try everything. There is no fuel leak anywhere. There is no smell of
fuel anywhere. Aux fuel pump keeps clicking as if pressure is not being
built up, but no leaks. Primer feels like it is pumping fuel into
cylinders. Sumping fuel reveals no water. We try switching tanks. Once
the first kick happened, NOTHING would get it to fire.

So we're planning a long XC in a couple of weeks. I'm concerned that even
if our mechanic does something, we might still not have it fixed and then
we could get stuck at some podunk airport. Although I thought the problem
had been fixed previously, the symptoms are the same, minus apparent fuel
leaks anywhere.

It acts like it's not getting fuel. The fact that the initial crank fired
suggests it's not electrical. But the fact that the primer feels like
it's pumping fuel means it should fire after priming, at least for a bit.

Anybody have good ideas?

Thanks in advance.

In article ,
Prime wrote:

Perhaps somebody here has an idea about this little problem.
[snip]

It sounds like a flooded engine, complicated by a weak battery.

it is normal for the electric fuel pump to keep clicking. What was
the reading on the fuel pressure gage?

where was the fuel on the carpet? Under the primer or near
the fuel selector?

btw - it's a long story, but we discovered a small fuel leak in
my cherokee 140. It wasn't the primer, it wasn't the fuel selector,
it was a compression fitting in the fuel line from the left tank.
Someone had used fuel sealant on it.

I assume from your post that the engine is cranking.

Did your mechanic check the mags and mag timing? How many
hours on your mags?

--
Bob Noel
Looking for a sig the
lawyers will hate

Careful, if this is happening just after the annual then your mechanic
has made some serious mistake somewhere. Question him as to just what
he did regarding the fuel system. My guess he fouled up the fuel tank
selection valve.

If that pump keeps clicking fast it might be because of low
voltage. It can't get full travel, since it causes a voltage drop and
the solenoid releases before it has taken in fuel and so won't build
fuel pressure. The engine's refusal to crank is another indication of
electrical problem.
Dirty battery terminals. Corroded cable terminals, where
they're crimped to the wire. An old, worn master solenoid and probably
starter solenoid, too. If the battery is fully charged and it still
won't crank, you need to start measuring voltage drops across terminals
and solenoids while attempting to crank.

Dan

He already explained jumping the airplane battery from a car.

He already explained jumping the airplane battery from a car.

That makes absolutely no difference if the master or starter
solenoids are defective, or if cable crimps are corroded. All that
amperage can't reach the starter if there are bad connections
elsewhere. We regularly find bad solenoids in older airplanes, and the
only way to fix it is to either start replacing them, or getting smart
and checking voltage drops across them while cranking. The copper
contacts in them oxidize with age, even in low-time airplanes, and will
be burned in higher-time aircraft. It only takes a fraction of an ohm
to stop things.

Dan

On Mon, 29 May 2006 02:27:18 -0500, Prime
wrote:

snip

pressure. The primer seemed to have fuel. I noticed fuel on the carpet

You noticed fuel on the carpet? In the plane? If there is fuel in
the cabin, that needs to be addressed immediately. You may have a
leak in the fuel selector valve or in the primer line.

-Nathan

A few other things to consider. If the impulse couplings in the magneto are
not working, you will not get a hot enough spark to start the engine.

The original aluminum power cables that were installed in the Cherokees
develop high resistance with age and cause weak cranking and a difficult
start when the engine is flooded. Replacing them with copper gives an
impressive improvement in cranking power.

--
Best Regards,
Mike
http://photoshow.comcast.net/mikenoel

'The first rule of intelligent tinkering is save all the pieces.' - Aldo
Leopold
"Prime" wrote in message
...
Perhaps somebody here has an idea about this little problem.

A few weeks ago, shortly after annual, I tried to start our Cherokee 140.
It kicked for a few revs, and then failed to start no matter what I did.
I noticed the aux fuel pump kept pumping, as if it was not building
pressure. The primer seemed to have fuel. I noticed fuel on the carpet
and leaking outside below the aux pump. We had our mechanic replace the
aux pump gasket a few days later. I then flew the plane twice after that
without any problems.

So today (a gorgeous day, by the way), my partner and I are going to fly.
We try to start the plane and it kicks once, then fails to start. We try
more primer. We try flooded procedures. Eventually the plane is cranking
slowly due to weakened battery. We get the car over and jump the plane.
We try everything. There is no fuel leak anywhere. There is no smell of
fuel anywhere. Aux fuel pump keeps clicking as if pressure is not being
built up, but no leaks. Primer feels like it is pumping fuel into
cylinders. Sumping fuel reveals no water. We try switching tanks. Once
the first kick happened, NOTHING would get it to fire.

So we're planning a long XC in a couple of weeks. I'm concerned that even
if our mechanic does something, we might still not have it fixed and then
we could get stuck at some podunk airport. Although I thought the problem
had been fixed previously, the symptoms are the same, minus apparent fuel
leaks anywhere.

It acts like it's not getting fuel. The fact that the initial crank fired
suggests it's not electrical. But the fact that the primer feels like
it's pumping fuel means it should fire after priming, at least for a bit.

Anybody have good ideas?

Thanks in advance.