Fuel system trouble

[Luke]

Hi all. My '84 M20J is going into the shop this week with a fuel system issue. I'm sure my A&P will be able to spot the problem but I'm just curious... Would love to know what folks think about what might be going on.

Saturday- started up fine, though the engine ran rough for maybe 10 seconds after firing up. Run-up was completely clean and had an smooth 2 hour flight.

Sunday- a similar rough start followed by a clean run-up. On the return trip I had a sneaking suspicion that my fuel burn seemed higher than usual (maybe 0.3 gph). She didn't seem to want to run smoothly LOP but I haven't done this much as it's a new-ish engine, so didn't think much of it.

Monday- Didn't start and barely got her to cough. Fuel flow reading was all over the place during my start attempts. Getting out of the cockpit I saw a steady stream of fuel coming out of one of two (not both) rubber hoses that are right next to the breather tube inside the left cowl flap. It left a decent sized puddle of avgas on the ground. Scary and I wonder what would could have happened if I was in the air!

My best guess was going to be that one side of the engine has a fuel system issue, but I'm interested to hear from those with more experience. I'm actually not sure what the purpose of the two rubber hoses I mentioned are and would love to know.

I have about 100 hours on a Lycoming factory overhaul so hopefully they'll stand up to the warranty... we'll see!

[carusoam]

Welcome aboard, Luke...

How Long have you had your Mooney?

Sounds like a real fuel flow issue problem... 

air leaking in, is often fuel leaking out.

On a new installation, anything can be suspect.  

Can you check all the fuel lines around the engine?

Did you smell any fuel while in flight...

Look for blue stains anywhere.  These often give a hint.

Definitely, not normal M20 behavior... better to check in with a mechanic than to go fly.

PP thoughts only, not a mechanic....

Best regards,

-a-

[Luke]

42 minutes ago, Luke said:

Sunday- a similar rough start followed by a clean run-up. On the return trip I had a sneaking suspicion that my fuel burn seemed higher than usual (maybe 0.3 gph). She didn't seem to want to run smoothly LOP but I haven't done this much as it's a new-ish engine, so didn't think much of it.

 

I got her back in August. She needed an engine overhaul at the time and we went with the factory one to get roller tappets and the other good stuff.  She's been a pleasure to fly!

[carusoam]

Often rough running is caused by...

• lead build-up on spark plugs...
• oil dripping onto the spark plugs....
• air leaking into a cylinder...
• fuel not getting to where it needs to go...
• blocked fuel injector...

Do you have an engine monitor?

Can you post some data?

Best regards,

-a-

[Luke]

That's a great idea, I'll pull some data off the EDM 900 when I'm out next. I didn't have my laptop with me last night.

[carusoam]

Time to identify what tube that is streaming fuel...

Might be as simple as the sniffle valve...  a check valve that may not be working properly, allowing air in at the wrong time and fuel out at another time...

could also be a failed diaphragm of a fuel pump.  Electric or mechanical...

Search on sniffle valve to find more...

Decowl, take pictures, know what is in there under the cowl...  all important for a PP to know...

As for FF being off by 0.3gph?  Twisting the mixture knob will hide that...  unless you compare to previous flights using a standard such as same MP, 20°F LOP... (Not really a standard standard... but, a comparable piece of data)

When you describe ‘good sized’ that is hard for other people to understand how much... puddle dimensions? Drips per minute? Pics always help...  this happened in X minutes....  

PP ideas only, not a mechanic...

Best regards,

-a-

[Luke]

I like the sniffle valve theory. I'll see if I can snap some pictures when I'm out next!

Interestingly, the fuel pressure has been high (30-31psi always) since the engine came back from Lycoming. even with the boost pump off. The A&P who put the engine back in said to not worry about it.

[carusoam]

Can you believe....?

We have a thread or two for that as well....  

Something changed with new fuel pumps.

Best regards,

-a-

This is an example of a search result on MS...

 

[Luke]

Yup that makes sense with the new Lycoming fuel pumps. The only issue it causes me is that the EDM-900 has a non-adjustable alarm that goes off at 30psi, which is pretty annoying.

[jaylw314]

2 hours ago, Luke said:

Monday- Didn't start and barely got her to cough. Fuel flow reading was all over the place during my start attempts. Getting out of the cockpit I saw a steady stream of fuel coming out of one of two (not both) rubber hoses that are right next to the breather tube inside the left cowl flap. It left a decent sized puddle of avgas on the ground. Scary and I wonder what would could have happened if I was in the

One of the hoses coming out of the left flap is connected to the sniffle valve in the intake manifold.  I can't imagine that is the problem, since there should NOT be a steady stream of fuel coming out of it after a normal start.  After a flooded start, or maybe after a bunch of failed starts, but not a normal one.  According to Don Maxwell, there is only one outlet for the intake drain (the other is a weep drain for the fuel pump), so it does not tell you the problem is only on one side, although it might be.

Of course, if the fuel was all coming out of the fuel pump weep drain, that would kind of narrow down the problem to the fuel pump. 

[Luke]

I'll get under the cowling and see where those lines go. Man I would feel dumb if I just flooded it. 

[jaylw314]

Here's the quote from Don Maxwell on what the three tubes do:

“J” models have the breather/ vent, mechanical pump “weep” drain and induction drain all located in the left cowl flap area.

[ArtVandelay]

Yup that makes sense with the new Lycoming fuel pumps. The only issue it causes me is that the EDM-900 has a non-adjustable alarm that goes off at 30psi, which is pretty annoying.

If you have official documentation from Lycoming that gives the fuel pressure range, you can send the unit back with the paperwork and they will adjust the alarm settings. Call them up and asked them what they need, they are pretty picky..I think it has to be a page from the POH.

[jaylw314]

1 hour ago, teejayevans said:

If you have official documentation from Lycoming that gives the fuel pressure range, you can send the unit back with the paperwork and they will adjust the alarm settings. Call them up and asked them what they need, they are pretty picky..I think it has to be a page from the POH.

The M20J POH has fuel pressure 14-30 in the Limitations section, though, and the aircraft POH supercedes the Lycoming POH, right?

[ArtVandelay]

You should get pages that are inserted into your POH with the new engines limitations. I believe the correct procedure is to draw a line through the old limits with notation “superseded by new engine limits” and a new page inserted right after it.
Anyone who has added an aftermarket turbo, long range fuel tanks, electronic ignition, etc should also have new POH pages.

[jaylw314]

30 minutes ago, teejayevans said:

You should get pages that are inserted into your POH with the new engines limitations. I believe the correct procedure is to draw a line through the old limits with notation “superseded by new engine limits” and a new page inserted right after it.
Anyone who has added an aftermarket turbo, long range fuel tanks, electronic ignition, etc should also have new POH pages.

That would not apply to people who get a normal overhaul or convert to the IO-360A3B6, right?  Since they're all under the original M20 TCDS, they would still go by the POH limits?

[carusoam]

POH updates often occur with STCs... Part of the STC is the proper pages or details to add to the POH.  Any WnB issues are covered at the same time...

Another thing that doesn’t get mentioned very much anymore... Any updates of a POH can be handled by a subscription... Mooney used to do this in the past.  There was a mail in card back in the day, at the front of the POH, to get on their mailing list....

This fuel pressure issue is kind of perplexing... Lycoming has supplied a fuel pump that operates at a higher fuel pressure....  this fuel pressure is beyond the existing redline authorized by the airframe manufacturer....

It probably takes an engineering document from Mooney to produce the authorization allowing for a new redline...

Byron gave the advice (above) of calling each day until this gets taken care of. 

Mooney updates the airframe paperwork to match the engine manufacturer’s paperwork, this all gets sent to the people at JPI so that the new redline can be programmed in properly....

EZ PZ... ya?

I would bet Mooney knows about this already, has a solution, but can’t find the owners that are affected...

Time to make a call...?

Best regards,

-a-

[Guest]

As one can not fly just an engine, the airframe PoH limits apply regardless of what Lycoming says or does. The 115 psi oil pressure limit is another example.

Clarence

[Luke]

22 hours ago, M20Doc said:

As one can not fly just an engine, the airframe PoH limits apply regardless of what Lycoming says or does. The 115 psi oil pressure limit is another example.

Clarence

Yep. I spoke with JPI, who said they'll only adjust limits based on an airframe STC. I've reached out to Lycoming and Mooney as well but I'm not particularly optimistic.

[N201MKTurbo]

25 minutes ago, Luke said:

Yep. I spoke with JPI, who said they'll only adjust limits based on an airframe STC. I've reached out to Lycoming and Mooney as well but I'm not particularly optimistic.

You should have your IA contact his principal inspector to see about a field approval to raise the limit. Get a letter from the FAA saying it is OK then send the letter to JPI and see if that would be OK to change the limits. That would all be proper and legal. Then have your IA send in a 337 with the limit change.

[jaylw314]

51 minutes ago, N201MKTurbo said:

You should have your IA contact his principal inspector to see about a field approval to raise the limit. Get a letter from the FAA saying it is OK then send the letter to JPI and see if that would be OK to change the limits. That would all be proper and legal. Then have your IA send in a 337 with the limit change.

Would it not make more sense to contact Lycoming for warranty work since their repair work is out of limits?

Edited March 21, 2018 by jaylw314

[N201MKTurbo]

4 minutes ago, jaylw314 said:

Would it not make more sense to contact Lycoming for warranty work since their repair work is out of limits?

You could try that too.

[N201MKTurbo]

FWIW, I asked the engineer from Precision Airmotive what fuel pressure the RSA-5 would accommodate and he said 60 PSI.

This was at the FAA maintenance symposium a couple of weeks ago.

[takair]

I ran into this when I changed my mechanical pump.  Mooney indeed knows about it, but would not offer a solution in the form of updated limits.  Lycoming simply says the new pump is within limits, because the engine can handle it.  In the end I sold the new pump to a friend with a Piper and bought a new, old part number pump.  One can file a service difficulty report if you can figure out how.

[ArtVandelay]

The engine fuel pump part numbers is listed in the TCDS, if it’s different I would expect a call to the FAA telling them Lycoming change part numbers would result in the Lycoming getting a unpleasant call from the FAA.