Fuel pump leak?

[Nippernaper]

Just got my J back from a top overhaul, and noticed a couple of fuel drips from a tube that exits the pilot side cowl flaps (picture below). What are the possible sources? I was thinking the fuel pump, but want to know what else it might be, and how to isolate it.

 

 

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[N201MKTurbo]

The big one is the crankcase breather, the two small ones are the mechanical fuel pump drain and the sump drain. The sump drain will leak some oil if oil drains from your valve guides after shutdown. It will drain fuel if you run the electric fuel pump with the engine off. The fuel pump drain should not drain anything. It indicates a bad diaphragm in the pump.

A few drips from the sump drain is nothing to be concerned about.

[Nippernaper]

The big one is the crankcase breather, the two small ones are the mechanical fuel pump drain and the sump drain. The sump drain will leak some oil if oil drains from your valve guides after shutdown. It will drain fuel if you run the electric fuel pump with the engine off. The fuel pump drain should not drain anything. It indicates a bad diaphragm in the pump.
A few drips from the sump drain is nothing to be concerned about.

Thanks, that helps. I'll keep an eye on it and see if it gets any worse.


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[Yetti]

Do a leak down test on the mechanical fuel pump.

Don Maxewell has a sniffle valve article.

If you are not leaning aggressively you will get some fuel out of the sniffle valve.   on stableized rollout after landing I go to about 1/3 mixture.  Then pop the door....  cause it's texas

[Nippernaper]

Do a leak down test on the mechanical fuel pump.
Don Maxewell has a sniffle valve article.
If you are not leaning aggressively you will get some fuel out of the sniffle valve.   on stableized rollout after landing I go to about 1/3 mixture.  Then pop the door....  cause it's texas

Ah, this is making sense now. I'm breaking in overhauled cylinders, so am running very rich to keep temps down, which explains why I'm seeing fuel drip from the induction drain. Just to be sure, is there a good reference for doing a leakdown test on the mechanical pump? Is this just tracking pressure after shutdown to see how long it holds?


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[Yetti]

do the normal start up procedure.

mixture closed.

turn on the fuel pump

Open mixture

count to 6

Close mixture.

The fuel pressure should hold for a couple of minutes.

If the diaphragm in the mechanical fuel pump is good.   The fuel pressure will hold.

[jaylw314]

If you want to make double-sure which hose is the intake manifold drain, just have someone hold a bucket under them while you run the electric pump, and then just give it half-mixture or so.  Fuel should come out the intake drain.  Have your friend make a note of which hose it is.

[carusoam]

+1 on sniffle valve diagnoses....

-1 for nylon ty-wraps on aluminum tubes....

Recommend becoming familiar ty-wraps ability to cut through things easily over time.

The ends of open drain tubes aren’t very critical... but they may be used on other tubes under the cowl that would be more critical...

Ask your mechanic if he has more of these with the new installation....

PP thoughts only, not a mechanic...

Best regards,

-a-

[Nippernaper]

Thanks all, this is great advice.  The shop that did the major overhaul for the previous owner didn't do a great job, and I've been removing ty-wraps as I go along.  These are some of the last ones left.

[Yetti]

9 hours ago, carusoam said:

 

-1 for nylon ty-wraps on aluminum tubes....

Recommend becoming familiar ty-wraps ability to cut through things easily over time.

 

What no honorable mention for not commenting on the overuse and improper placement of ty-wraps?   I was trying to ignore them in the picture......    But why is one of the screws painted and the rest stainless.   Gaaahghhhh

[Yetti]

And why is that panel with the mismatched screws not smooth.  That is a couple of knots right there.

[ArtVandelay]

Thanks all, this is great advice.  The shop that did the major overhaul for the previous owner didn't do a great job, and I've been removing ty-wraps as I go along.  These are some of the last ones left.

Mine looks exactly like yours, how else would you secure the 3 tubes/hoses?

[DonMuncy]

I have read on MS several times that nylon ty raps would cut into aluminum tubes. I'm not contending this is untrue, but has anyone seen a ty rap actually do that, or make a discernable groove in the aluminum.

[PT20J]

6 minutes ago, DonMuncy said:

I have read on MS several times that nylon ty raps would cut into aluminum tubes. I'm not contending this is untrue, but has anyone seen a ty rap actually do that, or make a discernable groove in the aluminum.

Yep, Don. Found it had worn half way through a one inch diameter aluminum oil supply line on the museum B-25. Hard to believe, but nylon is tough stuff. 

Now the one I can’t quite figure out is the claim I’ve seen more than once here (it’s also in Don Maxwell’s external tubing article on his website) that gas will drip from the sniffle after a normal shutdown. If you shut down by pulling the mixture to ICO, where does enough gas come from to collect in the bottom of the intake manifold?

Skip

[DonMuncy]

Just now, PT20J said:

Yep, Don. Found it had worn half way through a one inch diameter aluminum oil supply line on the museum B-25. Hard to believe, but nylon is tough stuff. 

Now the one I can’t quite figure out is the claim I’ve seen more than once here (it’s also in Don Maxwell’s external tubing article on his website) that gas will drip from the sniffle after a normal shutdown. If you shut down by pulling the mixture to ICO, where does enough gas come from to collect in the bottom of the intake manifold?

Skip

Thanks for the info Skip.

Incidentally, one of the tubes at my cowl flap drips a few drops of what appears to be fuel sometimes at shutdown. I assumed it was from the sniffle valve, but I have no idea where it comes from.

[carusoam]

1) Expect the case vent to drip condensed moisture and whatever else that comes with it... oil and other combustion byproducts...

2) The fuel injection system doesn’t give a lot of opportunity to drain excess fuel... when it does, usually, we are behind the controls...

3) Some people find it surprising that a piece of plastic can cut through a piece of metal...  over time we have learned nylon ty-wraps can cut through aluminum tubes...  it gets mentioned often because ty-wraps are great devices when used in the right places... and terrible when used to hold aluminum tubes...  like cockroaches... when you see one... there may be more. 

4) Often ty-wraps get mentioned because they aren’t cut off properly... and become a skin cutting hazard...

5) keep an eye on all aluminum tubes... they have a tendency to wear whenever they touch something hard while vibrating... they aren’t very thick, and they are very soft, so they can wear through quickly...

6) Tribology suggests that the hardness of a material will determine if it will wear, compared to the material that it is rubbing against...  in this case, nylon used in ty-wraps, simply, must be harder than the aluminum it is rubbing against...

PP thoughts only not a tribology expert...

Best regards,

-a-

[N201MKTurbo]

53 minutes ago, carusoam said:

6) Tribology suggests that the hardness of a material will determine if it will wear, compared to the material that it is rubbing against...  in this case, nylon used in ty-wraps, simply, must be harder than the aluminum it is rubbing against...

The nylon isn't harder than the aluminum, but the silica trapped in the oil crud under the ty-wrap is harder than the aluminum.

[jaylw314]

14 hours ago, PT20J said:

Yep, Don. Found it had worn half way through a one inch diameter aluminum oil supply line on the museum B-25. Hard to believe, but nylon is tough stuff. 

Now the one I can’t quite figure out is the claim I’ve seen more than once here (it’s also in Don Maxwell’s external tubing article on his website) that gas will drip from the sniffle after a normal shutdown. If you shut down by pulling the mixture to ICO, where does enough gas come from to collect in the bottom of the intake manifold?

Skip

I always assumed the fuel comes from the residual fuel in the divider that gets pushed out as it's heated by the cylinders after shutdown...

[Guest]

19 hours ago, DonMuncy said:

I have read on MS several times that nylon ty raps would cut into aluminum tubes. I'm not contending this is untrue, but has anyone seen a ty rap actually do that, or make a discernable groove in the aluminum.

Don,

Ive seen tyraps leave an impression in both steel and aluminum tubes.The nylon locking serrations will cut into4130 steel over time.  I’ve seen it several times.

Clarence

[PT20J]

13 hours ago, jaylw314 said:

I always assumed the fuel comes from the residual fuel in the divider that gets pushed out as it's heated by the cylinders after shutdown...

I think you are probably right. I have never witnessed this personally, but it does seem possible given the way the RSA fuel injection system functions. The mixture control is at the servo and there is a couple of feet of hose between the servo and the flow divider and another foot or so of line to each injector. The engine would run on for quite some time after moving the mixture control to ICO if it had access to all the fuel in those lines. To prevent this, a spring loaded valve in the flow divider cuts off fuel to the injectors when regulated pressure drops after selecting ICO. There is still residual fuel in the lines to the injectors, and I guess it could eventually drain into the intake manifold through the intake tubes and then out the sniffle drain. 

Skip

[jaylw314]

1 hour ago, PT20J said:

I think you are probably right. I have never witnessed this personally, but it does seem possible given the way the RSA fuel injection system functions. The mixture control is at the servo and there is a couple of feet of hose between the servo and the flow divider and another foot or so of line to each injector. The engine would run on for quite some time after moving the mixture control to ICO if it had access to all the fuel in those lines. To prevent this, a spring loaded valve in the flow divider cuts off fuel to the injectors when regulated pressure drops after selecting ICO. There is still residual fuel in the lines to the injectors, and I guess it could eventually drain into the intake manifold through the intake tubes and then out the sniffle drain. 

Skip

I gotta imagine there is still a few mL's of fuel left in all four injector lines put together, so if all those were pushed into the intake manifold, that'd be worth some visible drips at the drain...