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  #1  
Old 09-07-2017, 02:19 PM
bifft bifft is offline
 
Join Date: Feb 2012
Location: Utah
Posts: 121
Default Engine problem, help needed

Clear back in July, after 21 years building, had my first flight. Wrote it up here:

http://user.xmission.com/~bifft/rv/first.htm

On this flight, I did a stall test, and after that the engine wouldn't develop full power. Flew right back and landed. Trying to troubleshoot the problem, found that there was some junk in the throttle body's last chance filter. Thought that this was the cause of the problem. Rotec recommends a 40micron fuel filter, all I had was Van's gascolator.

I suspect I put the dirt into the system when I drained the tanks to fix some leaks. I drained into my old 5 gallon tanks I have used for chainsaw gas, off road trips, etc. Dirt probably came out of there.

So, added a 10 micron fuel filter, cleaned out the lines, flew again. Had the exact same problem. Takeoff and climb out are fine. Slow down to do a stall test, engine won't go back to full power. Can only run below 2000 rpm or so. Fortunately this is plenty to fly back to the airport and land. Inspection found only a few specks in the throttle body filter, a bit more in the larger filter.

Monday went back and flushed out the fuel system. Got a filter funnel (https://www.amazon.com/gp/product/B000SOIRCG) and used the planes fuel pump to pump back into my tanks, using the filter funnel both going into the tanks and back into the plane. Did get some junk in the funnel, including a dead bug. Probably out of my tanks. However the first five gallons and the last five both took 9.5 minutes for a 31 gph flow rate. Should be plenty.

Doing ground running after flushing the tanks everything ran great. However in my many ground runs I had not been able to replicate the problem. After a long ground run trying to simulate a climb out I could get full power. I decided to fly, and closed the hangar, put on my parachute, etc. Engine then would not start. I suspect vapor lock because of the heat soak from the long run. Oil temp and CHT both read 180. It was getting late, so went home.

This morning got out to the airport to try again. There were some delays on the ground waiting for the tower to talk to me, so the taxi out to the runup area took longer than usual, by the video 10:33 after engine start. This time I was able to replicate the problem on runup. Unable to get full power, stopping right around 2000 rpm. Video link goes to just as I am powering up to full throttle.

https://youtu.be/u0DnhU08hEE?t=80

I taxied back and did some more tests near the hangar. After 30 seconds or so with the fuel pump on I could get full power (2200 rpm) after a brief stumble. With the electric pump off, I can't. See later runups in same video:

https://youtu.be/u0DnhU08hEE?t=231


What do people think? What should I try next? Obviously I don't want to fly again until I can get this fixed.

Setup is O-360A1D with Rotec TBI, Catto 3-blade fixed pitch propeller. Fuel system is per plans, with Van's gascolator on the firewall. Added fuel filter between electric pump and gascolator, is on the cool side of the firewall.

I am leaning toward vapor lock as the cause. Possible fixes - remove gascolator? Have a better filter before it in the system, it currently is only catching water that I missed when sumping the tanks.

Fuel pump shroud and air line to engine fuel pump?

Also, the fuel line running from the pump to the TBI gets close to the exhaust pipe. I put on a heat shield, but that is probably not enough. Move the exhausts down so they go under the nose wheel mount? Re-route that fuel line so it is longer and less direct (maybe 2-3 inches longer), but farther from the exhaust?
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  #2  
Old 09-07-2017, 02:23 PM
F1R F1R is offline
 
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Only for the sake of possible causes, are your fuel vents open and adequately large enough?
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  #3  
Old 09-07-2017, 03:36 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,671
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What is your fuel pressure in flight? Specifically with the electric pump off and the airplane in a nose up attitude? Does it change with a nose down attitude or the electric pump on?

I'm wondering if you have a problem with the mechanical pump.
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  #4  
Old 09-07-2017, 04:36 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Vapor lock is not a likely suspect given that you had the problem in the air. Vapor lock usually only occurs on the ground or takeoff roll due to high heat and low cooling flow. I would spend more time confirming that the problem exists only with boost pump off and that it does not occur with the boost pump off. If that is the case, I would suspect the mechanical fuel pump.

Larry
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  #5  
Old 09-07-2017, 05:02 PM
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snopercod snopercod is offline
 
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Location: Asheville, NC
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I know absolutely nothing about your Rotec TBI, but the 180 degree oil temperatures you mentioned were messing up my MA-3SPA carburetor at idle. I suspected vapor lock at first but that didn't turn out to be the case. It was the heat from the oil sump heat-soaking the carburetor. Good luck.
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  #6  
Old 09-07-2017, 05:57 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
Posts: 3,888
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Is the Rotec is a low pressure system (3-6 psi)?

Is that 10 micron filter still in the sytem? If so, where? If it's before the engine driven pump, you may have solved one problem (trash) and created another (vapor lock). Running OK on the boost pump reinforces that theory.

If Rotec says 40 micron, then they've likely determined that 40 is good enough. Sometimes, 'better is the enemy of good enough' (although this is not the correct application of that particular saying).

10 micron filtering, even if the filter is clean, might well be a significant restriction on the low pressure side of the pump. How big is the filter element?

Last, gascolators are near perfect vapor lockers, when placed in the traditional location (low on the firewall, right in the 200 degree exit air, next to the radiant heat from the exhaust pipes).
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  #7  
Old 09-07-2017, 09:18 PM
bifft bifft is offline
 
Join Date: Feb 2012
Location: Utah
Posts: 121
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Quote:
Originally Posted by F1R View Post
Only for the sake of possible causes, are your fuel vents open and adequately large enough?
Fuel vents are 1/4" tubing as per plans, fuel does leak out when I overfill the tanks.
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  #8  
Old 09-07-2017, 09:28 PM
bifft bifft is offline
 
Join Date: Feb 2012
Location: Utah
Posts: 121
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Quote:
Originally Posted by Kyle Boatright View Post
What is your fuel pressure in flight? Specifically with the electric pump off and the airplane in a nose up attitude? Does it change with a nose down attitude or the electric pump on?

I'm wondering if you have a problem with the mechanical pump.
Reviewing videos, fuel pressure in flight is 4-5psi with electric pump off, 6 with electric pump on. Attitude doesn't seem to make a difference, but as this was first and second flight I didn't get very much up or down.

Per the Rotec manual 0.5 to 15 psi should work.
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  #9  
Old 09-07-2017, 09:40 PM
bifft bifft is offline
 
Join Date: Feb 2012
Location: Utah
Posts: 121
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Quote:
Originally Posted by rv7charlie View Post
Is the Rotec is a low pressure system (3-6 psi)?
Yes, low pressure.

Quote:
Is that 10 micron filter still in the sytem? If so, where? If it's before the engine driven pump, you may have solved one problem (trash) and created another (vapor lock). Running OK on the boost pump reinforces that theory.
Yes, filter was on system for second flight and today. It is installed between the electric pump and the firewall.

I got this one:

http://www.aircraftspruce.com/pages/...s/micron10.php

I wanted metal fittings instead of plastic. I calculate the 10 micron part is 1.48 in^2. I couldn't find a 40 micron that was metal instead of plastic. I did get the 31 gph flow even after running 40 gallons through it. That was with the electric fuel pump.

Quote:
Last, gascolators are near perfect vapor lockers, when placed in the traditional location (low on the firewall, right in the 200 degree exit air, next to the radiant heat from the exhaust pipes).
I put it a bit high on the firewall, but am still worried about that part.
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  #10  
Old 09-07-2017, 10:15 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,888
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Quote:
Originally Posted by bifft View Post
Yes, low pressure.



Yes, filter was on system for second flight and today. It is installed between the electric pump and the firewall.

I got this one:

http://www.aircraftspruce.com/pages/...s/micron10.php

I wanted metal fittings instead of plastic. I calculate the 10 micron part is 1.48 in^2. I couldn't find a 40 micron that was metal instead of plastic. I did get the 31 gph flow even after running 40 gallons through it. That was with the electric fuel pump.



I put it a bit high on the firewall, but am still worried about that part.
Here's the detail that jumps out for me:
"I taxied back and did some more tests near the hangar. After 30 seconds or so with the fuel pump on I could get full power (2200 rpm) after a brief stumble. With the electric pump off, I can't."

If the 10 micron pump is between the boost pump & mech pump, and the fuel between the filter & the mech pump is hot, it sounds like a recipe for vapor lock. The boost pump would pressurize the line, instead of the mech pump sucking on it, which would kill the vapor lock.

Not saying it's for sure the cause, but it should be easy to check; substitute a 40 micron or more filter.

You could also ask Rotec why they only spec'd 40 microns when 10 micron filters are available.

edit: Just re-read the above after posting. Are you saying that the filter area is less than 1.5 square inches?

Last edited by rv7charlie : 09-07-2017 at 10:23 PM.
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