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Engine stutter on right tank.


lifendet

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On a flight last night with 1/4 fuel in right tank engine started stuttering. Switched tank and engine ran fine. Landed, inspected tank but nothing obvious so I filled up both tanks and flew again. Switched from left to right and engine stutter again. Landed and switched to right tank while on ground. Engine ran fine with no hickup. Went up to power while on right tank and no problems. I'm lost... 

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Possible water in right tank.  

- When you fueled up last time was it raining?  

- Do you keep airplane outside?  If so, when was last time you changed fuel cap gaskets?  

- Do you top off after each flight or leave half empty?

- Did you sump before flight and look at sample real well?  

- Do you have an engine monitor?  If so, download and share with the group.  I also belong to SAVVY engine analysis and they will analyze your engine data.  Good to do for situations like this plus they can also analyze for overall engine health.  I had water in my tank last winter.  Symptom was a hiccup every now and then, no change in fuel flow or engine temps.  Sent off to SAVVY and between my debrief and their analysis we suspected a little bit of water.  Made sense because a couple of days prior when I fueled, it started to do a slight Florida winter mist towards the end of my top off.  No rain, no sprinkle, just a little mist.  A little water can create havoc. I put a half bottle of HEAT in and no issues.

- Do you have digital fuel flow?  did you look at it and see any fluctuations?

 

But hopefully and probably just a little water.  Other possibilities would be something in your lines coming off right tank through gasculator.  Was gasculator cleaned at last annual?

 

Just my initial thought from experience but I am sure you get a lot of input in here and a good direction to take next......

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1 hour ago, anthonydesmet said:

Possible water in right tank.  

- When you fueled up last time was it raining?  

- Do you keep airplane outside?  If so, when was last time you changed fuel cap gaskets?  

- Do you top off after each flight or leave half empty?

- Did you sump before flight and look at sample real well?  

- Do you have an engine monitor?  If so, download and share with the group.  I also belong to SAVVY engine analysis and they will analyze your engine data.  Good to do for situations like this plus they can also analyze for overall engine health.  I had water in my tank last winter.  Symptom was a hiccup every now and then, no change in fuel flow or engine temps.  Sent off to SAVVY and between my debrief and their analysis we suspected a little bit of water.  Made sense because a couple of days prior when I fueled, it started to do a slight Florida winter mist towards the end of my top off.  No rain, no sprinkle, just a little mist.  A little water can create havoc. I put a half bottle of HEAT in and no issues.

- Do you have digital fuel flow?  did you look at it and see any fluctuations?

 

But hopefully and probably just a little water.  Other possibilities would be something in your lines coming off right tank through gasculator.  Was gasculator cleaned at last annual?

 

Just my initial thought from experience but I am sure you get a lot of input in here and a good direction to take next......

I sump before I left, Aircraft kept in Hangar, no rain last time I fueled, haven't changed fuel cap since I bought it. I usually top off after each flight but the last flight I didn't. After switching tanks I noticed the FF had spiked but eventually came back to where I had it set. My mechanic has it now. Will update on findings. I use savvy as well... 

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4 hours ago, lifendet said:

I sump before I left, Aircraft kept in Hangar, no rain last time I fueled, haven't changed fuel cap since I bought it. I usually top off after each flight but the last flight I didn't. After switching tanks I noticed the FF had spiked but eventually came back to where I had it set. My mechanic has it now. Will update on findings. I use savvy as well... 

Hmmm, If you think you had a fluctuation in fuel flow it maybe something in a fuel line or fuel pump.  Although I would think if it were the pump you would have had issues on both tanks and had to go to boost.  If its a problem of fuel getting to the engine (and not a water issue) I would assume an obstruction of some sort.  You may also be able to verify on your engine download with a spike in temperatures due to low fuel (i.e. very lean for power setting) depending on how long the stutter was.  For my water episode there was no fuel flow change and just and just a minor fluctuation in CHT's.  Interesting that the fuel flow would spike over normal though when it should come down if you were stuttering for not enough fuel flow....interesting, looking forward to your update.

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Tell us more about the FF spike!

That isn’t a normal thing to have happen...

+1 for checking the fuel vent. Ask if you are not familiar...

With a blocked vent, the tank slowly builds a vacuum.  The wing skins start to oil can...

Long enough, the engine will not be able to over power it...

Anything that allows air back in resets the whole weirdness...

But, a FF spike... I’m not sure what would cause that... that sounds more like a fuel injection system problem... fuel divider, mixture control, spider things...

Wait a minute...

When air enters the fuel system... the fuel metering system maintains the fuel flow...  it will keep drawing fuel and air to get enough fuel.  The FF gauge can’t tell the difference and air bubbles get read like extra fuel is coming in...

Be on the look-out for air leaks into the fuel system... which often look like fuel leaks that have left the system... lots of blue staining.

Something doesn’t sound like it is delivering fuel the way it is supposed...

PP thoughts only, not a mechanic...

Best regards,

-a-

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I'm still thinking it's the tank vent blocked.

I'm assuming it was running fine on the right tank until it got down to 1/4 tank. (If there was water, you'd expect it to act up almost immediately, not burn 3/4 of a tank first)

If the valve was the problem, it wouldn't work on the ground any more than in flight.

I'm certainly following to hear the correct answer.

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Having a similar discussion with @Jim Peace regarding a leaking ferrule on his fuel pump line...

His leak is probably allowing air in during flight, fuel out while on the ground... (Jim is nothing higher FF indication as well)

One obvious difference is (if there is a leak)... where the leak may be.

Since changing tanks solves the problem the leak is possibly anywhere from the valve back to the tank....

Valves have been known to allow air into the fuel system...

One hint is blue stains around the selector handle.  Fuel gets out while the engine is not running... then evaporates...

One way to tell for sure... run fuel into a bucket using a clear hose... you will most likely see air bubbles in the line this way...

Somebody showed a video of this around here somewhere...

Requires a mechanic to do this...

Best regards,

-a-

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7 hours ago, gsxrpilot said:

I'm still thinking it's the tank vent blocked.

I'm assuming it was running fine on the right tank until it got down to 1/4 tank. (If there was water, you'd expect it to act up almost immediately, not burn 3/4 of a tank first)

If the valve was the problem, it wouldn't work on the ground any more than in flight.

I'm certainly following to hear the correct answer.

I was having that same thought about burning 3/4 tank before any signs.  But it still happened after he topped off. So I went down the road of contamination sometime during sitting with a 1/4 tank that was still there after you topped off. Funny thing about water.  Once it gets in and trapped behind a couple of the ribs, no matter how much you sump you might not get to it.....that’s why the HEAT.  But it sounds like he had pretty dry conditions during time leading up to flight.  I am leaning more towards the vent and air into system now I think......the fuel flow spike is weird......that’s a key debrief point I think..  I’d still really like to see the engine data

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Just got off the phone with my mechanic. I'm not convinced but his diagnosis was a spark plug was crossfiring and causing cylinder #1 to die hence the engine hiccup. He couldn't replicate fault either but he is convinced that was it. He couldn't give me a clear answer as to why it happened twice when I switched to right tank. No water was found, no fuel leak. 

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Just got off the phone with my mechanic. I'm not convinced but his diagnosis was a spark plug was crossfiring and causing cylinder #1 to die hence the engine hiccup. He couldn't replicate fault either but he is convinced that was it. He couldn't give me a clear answer as to why it happened twice when I switched to right tank. No water was found, no fuel leak. 

What did the engine data say? That would be the best way to validate his diagnosis.


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