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Old 04-10-2011, 11:15 PM   #1
PilotPete
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Default IO-540 sniffle valve

Does anyone know if there is a wiffle valve on the PA32 IO-540-K1G5D?
Also called a piddle valve or fuel drain valve. Lycoming p/n 75444 I believe.

It's purpose is to drain away any excess fuel in the induction system when the engine is off.

I'm trying to hunt down a possible induction leak and want to strike wiffle valve off my list of things to check.



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Old 04-11-2011, 03:50 AM   #2
magman
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Default Re: IO-540 wiffle valve

I don't recall any injected engine without one.

Add Sniffle Valve to your list of names.

If you're uncertain as to appearance & location you may:

1.Mixture Rich

2. Boost Pump -ON

Probably about 30 seconds later you will note fuel dripping on the floor.

Follow tubing & hose "Upstream"

Where the hose or tubing attaches to Sump (Plenum) is the fitting.

Once engine is started you should feel NO SUCTION here. A piece of hose may help.


You may want to connect a Shop Vac or Leaf Blower to your exhaust stack & close throttle.

You will pressurize exhaust system & Induction System as well.

Squirt with a soap & water solution.

BTW- Use caution with fuel .

Let excess drain before starting engine.



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Old 04-11-2011, 09:41 PM   #3
MarshallJ
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Default Re: IO-540 wiffle valve

The Sniffle valves (2) are on the back corners of the intake plenum and have hoses connected to drain back by the firewall. You can check them by blowing a little air into the hoses and there is a check ball in the valve that should close with a little pressure. If they don't you need to replace them, usually Preferred Air Parts has them. I find that the vacuum leaks from these valve are not that much to make much of a difference or at least is hard to tell. You just adjust the throttle or mixture to compensate and don't notice much. You didn't mention what the engine is doing for you to think that you are getting air into the fuel? One of Precsion Airmotive's trouble shooting sugestions is to put a piece of clear plastic tubing between the spyder (divider) and the fuel supply line and run the motor and see if there is air bubbles in the line. This will tell you that you have air in the fuel line but not where it is coming from. But from there you can start trouble shooting. One other note air in the fuel line and blockage in the line give the same symtems so you really need to find out if you have air in the line or not. I just did a complete trouble shoot of a fuel system on a PA32-300 and it ended up with two problems that allowed air into the fuel line. Let me know what the engine is doing and maybe i can give you a few ideas on what to check.
Marshall

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Old 04-12-2011, 03:04 PM   #4
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Default Re: IO-540 wiffle valve

Thanks guys! I know where they are now.

Marshall, my problem is not that I'm getting air into the fuel, but rather that I believe I may have a small induction leak on one bank of cylinders. My EGTs on the odd bank are somewhat higher (75-deg) than the even bank when running LOP. That suggests to me a bank-specific induction leak.

So if the 2 sniffle valves service the odd and even intake plenums, then that might be the problem - one is stuck open. Will check today and test as you have suggested and let you know what I find.

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Old 04-12-2011, 09:06 PM   #5
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Default Re: IO-540 wiffle valve

Pete
One little item that could affect one bank of cyclders on intake is the line that feeds the manifold pressure gauge. This line has a hole drilled in the back side of it where you normaly can't see it. They put this hole in the line to damp out the cylinder pulses on your gauge it is a controlled leak. Sometimes people will plug it thinking it is a defect in the tube and this will change the EGT's on one bank of cylinders and you should see a bouncing in your maniford gauage. You could also get a crack at the hole location and have a larger leak than you should have. You might have to use a mirror to find this hole,

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Old 04-12-2011, 09:24 PM   #6
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Default Re: IO-540 wiffle valve

Why would it only affect one bank of cylinders?

Can you confirm that one sniffle valve services the odd cylinders and the other services the evens?

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Old 04-12-2011, 10:29 PM   #7
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Default Re: IO-540 wiffle valve

They only take the maniford pressure off of one side but now that I think of it it is only cyclinder # 5 so it should only effect that one. Scratch that idea. The sniffle valves both feed into the open intake manifold, they aren't specifc to one side of the other so if they are not working it would effect all cyclinders. I would also check all the fuel injectors to make sure they are not clogged or restriced. One or two restricted injectors will increase the flow to all the others because this is a constant flow FI. Why are only one side being affected who knows, luck of the draw. Do the EGT's change with the boost pump on? Does this happen at all power settings or at only certain settings. Does anthing change with alt air on? Since you didn't mention any missing you should be able to rule out spark, and valve train. It only leaves fuel and air that would make three cyclinders run lean. Maybe you have an air leak where the intake manifold mounts to the oil pan or a crack/hole in intake? Sometimes the o-rings on the intake runners get twisted and they can leak but all three on one side seems unlikly. I'm leaning if you will excuse the pun toward a fuel delivery problem. Good luck let us know how it goes.

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Old 04-15-2011, 06:01 PM   #8
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Default Re: IO-540 wiffle valve

I extended the fuel drain hoses with clear plastic hose so I could test the valves by blowing into them.

There are 3 fuel drain valves and hoses on the IO-540 (left, right, and center) which agrees with the PA32R-300 parts manual (24995-00 VALVE ASSEMBLY - Automatic fuel drain).

Interesting findings:
1 closes up when blown into - what I expected.
1 is wide open no matter how hard I blow.
1 is closed tight and no air can pass.

So I may have found a couple of problems. One valve seems to be stuck closed which prevents fuel from draining as it should. One valve seems to be stuck open and that could have mixture implications, especially when running lean.

My plan is to run ~5' of hose extension into the side window opening for each of the 3 drain tubes opening, and go flying and see what kind of suction I get. Then I can cover the hoses with my finger and see what happens to the EGTs.

Any other suggestions before I start spending real money on this?

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Old 04-15-2011, 10:01 PM   #9
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Default Re: IO-540 wiffle valve

Just ran a ground test with the engine at ~1200rpm and leaned out until ~100rpm drop. Sure enough, the engine is sucking air through one of the valves. If I put my finger over the end of the tube, the MAP goes down about 1.5" and the RPM goes up about 100 rpm (running at ~1200 rpm). That makes sense - with less air, the mixture is less lean so should produce a bit more power.

It was hard to tell how the EGTs were affected, since the power was so low, but they definitely did move around when I covered and uncovered the end of the tube.

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Old 04-17-2011, 03:47 AM   #10
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Default Re: IO-540 wiffle valve

For those that care, I determined today that one of the 3 valves is actually a purge valve on the fuel pump. That's the one that seems to be completely blocked, but that makes sense as it is located on the backside of the mech fuel pump membrane and vents a sealed chamber. I understand it'spurpose is to vent fuel overboard in case the membrane bursts.

The other two valves are threaded into the bottom of the intake manifold, one on each side of the engine. Both parts are different, which leads me to believe that at least one of them is not the correct part. Both have a 90-deg bend on the hose end.

The parts manual for the IO-540 calls up qty2 Lyc p/n 75444 valves. Anyone know if the 75444 has a 90-deg bend in it? Anyone suggest a good place to order them from?



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