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  #1  
Old 10-14-2018, 12:28 PM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
Posts: 190
Default Short engine stumbles

Went up for flight this morning and ran into something new. I was in level flight at 60% power, mixture running at peak EGT or slightly below and I had a series of 3 short low fuel pressure events. Pressure dropped below 10 for 2 seconds, I could hear it in the engine sound, I got an aural alert from my Skyview EMS and I saw the fuel pressure gauge drop. Each event lasted about 5 seconds where pressure was below the normal 25 and they all resolved themselves. I responded to the first one by turning on the boost pump and pushing in the mixture all the way. The second event followed 30 seconds later and the last event a little more than a minute later. Fuel flow stayed steady through each event (corresponding with the state of the boost pump and mixture at the time) and I didn't see much change in the RPM although I'm on a C/S prop. After the third event I switched back to my left tank - I'd been on the right tank since about 5 minutes earlier. I didn't have any issues on the left tank and immediately returned to land. I did switch back to my right tank after landing and did an uneventful runup prior to shutting down.

I feel good about how I responded to the hiccups, I reacted quickly with the boost pump and mixture and was running through my immediate options including a precautionary landing at the small airport I had overflown a few minutes earlier. I had plenty of altitude, about 3500' AGL and I would have had about 4 minutes to get it down should the engine have quit.

My question for the brain trust here is this. Is this a highly unusual and concerning issue? I don't know what caused the stumbles, fuel contamination? air pocket? My data logs are pretty thorough, is there any other counter that would give a clue about the cause? I'm a little reluctant to go back out without some idea about what happened.

At least I found out that my autopilot works well as was the purpose of my flight today.
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RV-9A #91081, C-GCPT
Dynon SkyView HDX, IO-320 and WW 200RV C/S. Flying as of August 6, 2018
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  #2  
Old 10-14-2018, 12:59 PM
Tracer 10 Tracer 10 is online now
 
Join Date: Mar 2011
Location: Oregon
Posts: 86
Default Fuel flow on right tank.

Check for an obstruction in right fuel tank vent.
Loosen fuel caps on both tanks.
Take a piece of hose that will fit over the fuel vent & place it over the vent with firm pressure.
Blow air from your mouth into the hose & compare airflow that escapes from the fuel cap; on the left v/s the right side.
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  #3  
Old 10-14-2018, 08:20 PM
vlittle's Avatar
vlittle vlittle is offline
 
Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,023
Default

Good tip on checking the fuel vent.

Since this is a new aircraft, you should also check all of your fuel screens and filters for debris. This includes the gascolator, fuel pickups and servo finger screens plus any other inline filters.

Debris from the build may have been trapped in one or more filters. This is quite common.

V
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  #4  
Old 10-15-2018, 10:33 AM
Ivan Kristensen's Avatar
Ivan Kristensen Ivan Kristensen is offline
 
Join Date: Mar 2008
Location: Guelph Ontario
Posts: 218
Default Fuel pressure drop

A fuel pressure drop like you describe is not unusual during climb out but rarely during level flight. I suggest that you do the checks as described in the above posts but consider the following.

I battled this issue early on and changed the engine driven fuel pump. When that didn't help I installed the cooling shroud for the engine driven pump thinking that it was vapor lock in the fuel caused by heat. That didn't help either.
After quite a lot of research and flying I learned a number of things.

1. This is not an unusual phenomenon.
2. It almost always happen during climb out after the Aux. pump was turned off.
3. It happen more frequently during the hot summer months.
4. Happen most often when the tanks are full.
5. Many POH's recommend keeping the AUX pump on to the top of the climb.
6. Some Cessna twins have two speed AUX pumps. High speed during T/O and
climb and low speed continuously during cruise.

In summary, I now keep the AUX pump on until the cruise portion of the flight and that has eliminated this problem entirely. Well almost!! The fact is that I will still see a momentary drop in Fuel pressure in level flight, some times months apart, but again it is always when the tanks are full.
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  #5  
Old 10-15-2018, 11:15 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 430
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Hey Claude
Sorry to hear you are still sorting out the ‘bugs’. Thought they would have been killed off by our preview to ‘winter’!
Option one would be continue flight knowing you have 19gal Unusable Fuel on the right side, undesirable for sure. Plus it would be prudent to assume the same problem might happen to the Left as well... later.
Option two though unpleasant, is the path I’d recommend. Open up All the plumbing to the tanks & examine everything until you determine the absolute cause of the blockage, before further flight.
Fuel systems are one of the things that should have no questions left lingering.
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  #6  
Old 10-15-2018, 11:36 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 3,314
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While lots of folks see varying fuel pressure at times, they are mostly instrument issues or reductions in the pump's output that don't fall below what the engine is consuming and produce no engine symptom (the pumps delivery capcity is 3 times what most 4 cylinders need and when the output begins to fall off, the pressure drops along with it); Myself included. This excludes heat issues, like taking off after a heat soak or taxiing. Any reductions in pressure with a corresponding symptom of fuel starvation should be immediately addressed, as something is wrong, especially an intermittent issue like yours. This should not be ignored. If it was a blockage and didn't clear itself fully, you could find yourself in a situation where the boost pump won't resolve it and if the blockage is downstream of the selector, a tank change won't fix it either. Be advised that many times, a blockage is caused by a loose piece of debris that will only occassionally position itself in a position that causes reduced fuel flow. If it exists, it is a ticking bomb.

The most common cause for an intermittent issue like this (assuming it was not precipitated by something like a tank change) is blockage or a failing fuel pump. A venting problem would not likely show up instantly and disappear in 5 seconds. You would usually see the pressure slowly drop as the vacuum in the tank builds. Venting issues are also not easily addressed with the boost pump, though often the boost pump is stronger and can pull a stronger vacuum and deliver fuel longer with a clogged vent.

Given this a new engine, blockage is at the top of the list. However, don't discount the pump. The pump could have a manufactured defect. Parts like this don't roll of the line with a 0.0% defect rate. Odds are low, but not non-existent. Another possibility is something large floating in the tank that occassionaly blocks the strainer. Vans even has an SB out for plastic left in the tanks. It happens.

Do you have a carb or FI? Air bubbles causing symptoms are not common and virtually non existent in a carb. The exception being constant bubble streams due to leaks in the fuel circuit upstream of the pump.

Larry
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Last edited by lr172 : 10-15-2018 at 12:17 PM.
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  #7  
Old 10-15-2018, 11:37 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 4,543
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Quote:
Originally Posted by Flying Canuck View Post
My question for the brain trust here is this. Is this a highly unusual and concerning issue? I don't know what caused the stumbles, fuel contamination? air pocket? My data logs are pretty thorough, is there any other counter that would give a clue about the cause? I'm a little reluctant to go back out without some idea about what happened.
Concerning: yes
Unusual - it does happen, I had one, but clearly link it to hot and slow in the pattern. I have a temperature logger ordered for the evaluation process.
What: Hmm, good suggestions so far. Vent, debris, floating shop towel etc.

- Also, look at FWF for exposure of lines/hoses with direct view to hot exhaust pipe. (you did not mention having issues when hotter, so maybe no factor)
- Might go back and check data for fuel pressure wandering for previous 10 flights, see if it is recent and only limited to one tank.
- I would drain fuel on that side and pressurize with 30 psi air (between fuse and firewall), and leave to sit for a few hours to evaluate for leaks. My 7, and friends 10, held 30 psi overnight. A tiny suction leak can cause trouble like this and would leak air profusely.


Quote:
Originally Posted by Ralph Inkster View Post
Hey Claude
Option two though unpleasant, is the path I’d recommend. Open up All the plumbing to the tanks & examine everything until you determine the absolute cause of the blockage, before further flight.
Fuel systems are one of the things that should have no questions left lingering.
As above, definitely #2. It is better to evaluate all known possibilities and not find something, then it narrows the list if it happens again.

2 cents
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Last edited by BillL : 10-15-2018 at 11:42 AM.
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  #8  
Old 10-15-2018, 12:20 PM
Flying Canuck Flying Canuck is offline
 
Join Date: Jan 2015
Location: Red Deer, Alberta, Canada
Posts: 190
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This is a fuel injected engine. My right tank was 7 minutes below full and I was level for the preceding 20+ minutes and straight for nearly 10 minutes. It was the coldest day that I've flown so far - OAT was +1C at the time of the trouble. I checked all of my flights to date and this was the first occasion of low fuel pressure that I found.

I don't really suspect anything forward of the fuel selector as the left tank wasn't showing any signs of the problem. A venting problem is certainly possible. I suppose debris in the tank is possible too - I did flush it out while calibrating my fuel sender and definitely saw some debris. There wouldn't be any screens in the tank and the first filter is at my boost pump.

Thanks for all of your suggestions. I will first check for an obvious obstruction in the right vent. Failing that and while I really don't like the idea given the fact that the weather is finally looking like it might let me fly, I'm going to drain the right tank and see if I can get my scope in there for a look see. The idea I don't like and won't do is rolling the dice and hoping the problem doesn't come back.
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  #9  
Old 10-15-2018, 12:34 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 3,314
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Quote:
Originally Posted by Flying Canuck View Post

I don't really suspect anything forward of the fuel selector as the left tank wasn't showing any signs of the problem.
Food for thought: Prior to yesterday morning and even after the event, you right tank wasn't showing any signs of the problem either. I don't believe you have enough data to rule out the left tank or the rest of the system. It could easily be coincidence that it only occurred on the right tank. Nothing wrong with starting where your intuition points you, but please don't ignore the rest of the system if you don't find an issue there.

Be safe.

Larry
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Last edited by lr172 : 10-15-2018 at 12:39 PM.
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  #10  
Old 10-15-2018, 04:01 PM
Boyd Birchler Boyd Birchler is offline
 
Join Date: Sep 2014
Location: IN
Posts: 161
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I see no one has said anything about a loose connection. I have seen connections that would not leak fuel, but would suck air enough to cause this type of problem. If the phenomena is truly only on one side of the fuel system it should be easy to address. Starting at the fuel selector checking each connection for tightness until the tank.
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