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  #1  
Old 03-04-2018, 03:28 PM
jj13 jj13 is offline
 
Join Date: Aug 2012
Location: Dunwoody GA (KLZU)
Posts: 62
Unhappy Low fuel Pressure Root Cause maybe

I have a fuel inject Superior 320. Over the last few months I have been experiencing intermittent low fuel pressure until now where it is consistently low (5 - 10lb) The backup pump must be run for the engine to stay running. Knowing that the engine driven fuel pumps are very reliable I started looking else where. What I found is what appears to be a failure with the fuel plunger and the cam(see the pic)

So I have two questions; any ideas how this could happen, could this be a defect in the plunger or cam?

Second - To fix this will obviously require pulling the engine and accessory case. What I was thinking was just adding a second electric fuel pump forgoing the mechanical pump. I have dual electronic ign, so I'm already electrically dependent. My bigger concern is hot starts. The mechanical pump vs. the full pressure of the electrical pump on startup.

any help would be greatly appreciated!

https://drive.google.com/open?id=11R...rDkMaiadZ_muyw
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  #2  
Old 03-04-2018, 04:06 PM
chevelle000 chevelle000 is offline
 
Join Date: Sep 2017
Location: Mesa,AZ
Posts: 92
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John, you better pull your engine ASAP. If the plunger has worn down that much all the metal has gone through your engine. Pay special attention to the oil pump.
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  #3  
Old 03-04-2018, 07:11 PM
RV7 To Go's Avatar
RV7 To Go RV7 To Go is offline
 
Join Date: May 2011
Location: Ontario, Canada
Posts: 321
Default Rebuild

Quote:
Originally Posted by chevelle000 View Post
John, you better pull your engine ASAP. If the plunger has worn down that much all the metal has gone through your engine. Pay special attention to the oil pump.
+1 I am not aware that this has been an issue with Lycomings. I don't know why it happened but based on your pic the only solution is to pull the engine and split the case to replace the cam, check the oil pump, check the case, main bearings and cylinder walls for scoring. I had a similar issue when my cam was destroyed 34 hrs after being rebuilt due to the tappets not being properly reconditioned. I feel your pain. Better you found it on the ground rather than the air!

On the issue of hot starts, in the forums Dan H had a very good explanation of a hot start procedure that works well. I don't think dual electric pumps is necessarily the answer.
Al

Last edited by RV7 To Go : 03-04-2018 at 07:18 PM.
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  #4  
Old 03-04-2018, 10:28 PM
heinz heinz is offline
 
Join Date: Sep 2010
Location: comox bc
Posts: 52
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The "cam" is not on the camshaft. The cam that pushes the fuel pump plunger is on one of the crankshaft idler gears. The amount of wear on your pump plunger is serious enough to warrant repair, but if you have an oil filter, it has unlikely caused any damage as suggested by the previous post. The repair can be made without splitting the crankcase. Remove the accessory case and replace the idler gear and the plunger. Further to this, the amount of wear on the plunger appears to be not enough to keep the fuel pump from working. Good luck.
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  #5  
Old 03-05-2018, 07:58 AM
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storm_pilot storm_pilot is offline
 
Join Date: Apr 2017
Location: ND, D54
Posts: 20
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You mention "Knowing that the engine driven fuel pumps are very reliable I started looking else where." Before taking anything else apart verify that the pump is indeed putting out the recommended pressure. Yes they are reliable but stuff does happen. Also check all of your fuel screens and filters if installed. Look for the simple stuff first ;^)
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  #6  
Old 03-05-2018, 01:47 PM
Boyd Birchler Boyd Birchler is offline
 
Join Date: Sep 2014
Location: IN
Posts: 254
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Some times funny indications are because of indicator errors,problems with senders,wiring etc. Sometimes fuel pressure fluctuations are caused by a leak in the suction side of the fuel system that may admit air in but strangely not leak fuel out (gascolators are famous for this). Sometimes it is vapor boiling in the gascolator.
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  #7  
Old 03-05-2018, 06:49 PM
jj13 jj13 is offline
 
Join Date: Aug 2012
Location: Dunwoody GA (KLZU)
Posts: 62
Default Thank you for your valuable responses and ideas

Some are saying that the plunger / cam may not even be the root cause and I agree. I will continue to check the fuel lines, connections and filters. With that said I will have to replace the plunger and gear if I want to continue to use the mechanical fuel pump, and that will require pulling the engine to get access to the accessory case which I really don't want to do

So I'm thinking of just adding another electric fuel pump and be done with it. I believe I can do that much quicker and not lose out on all this good flying weather this time of year. Plus I'm least familiar with the engine and feel more confident adding the fuel pump.

Aero Sport Power whom I bought the engine from will be giving me their recommendation along with why they believe the failure of the plunger occurred tomorrow. I'll post that once I receive it.
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  #8  
Old 03-05-2018, 08:46 PM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
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Quote:
Originally Posted by jj13 View Post
Some are saying that the plunger / cam may not even be the root cause and I agree. I will continue to check the fuel lines, connections and filters. With that said I will have to replace the plunger and gear if I want to continue to use the mechanical fuel pump, and that will require pulling the engine to get access to the accessory case which I really don't want to do

So I'm thinking of just adding another electric fuel pump and be done with it. I believe I can do that much quicker and not lose out on all this good flying weather this time of year. Plus I'm least familiar with the engine and feel more confident adding the fuel pump.

Aero Sport Power whom I bought the engine from will be giving me their recommendation along with why they believe the failure of the plunger occurred tomorrow. I'll post that once I receive it.
If you've got metal spalling off the plunger/cam, you're playing with fire and the clock is ticking by continuing to fly. It's not IF, but WHEN you're going to have bigger problems. That needs to be addressed.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #9  
Old 03-05-2018, 10:57 PM
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RV7 To Go RV7 To Go is offline
 
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Location: Ontario, Canada
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Quote:
Originally Posted by heinz View Post
The "cam" is not on the camshaft. The cam that pushes the fuel pump plunger is on one of the crankshaft idler gears. The amount of wear on your pump plunger is serious enough to warrant repair, but if you have an oil filter, it has unlikely caused any damage as suggested by the previous post. The repair can be made without splitting the crankcase. Remove the accessory case and replace the idler gear and the plunger. Further to this, the amount of wear on the plunger appears to be not enough to keep the fuel pump from working. Good luck.
My mistake for not differentiating between the fuel pump cam gear and my camshaft issue.

My engine had a filter. The first oil change was done at 10 hrs with only a trace of metal after the rebuild, which was considered ok by our local guru. The second change after another 24 hrs resulted a magnet full of metal particles upon cutting the filter. As the camshaft wore the metal first goes into the sump prior to entering the pump and filter etc. Upon tear down the new pump was badly scored, the new nitirided cylinders were scored, all the new bearings had metal impregnated in them.

The above experience is why I suggested pulling the engine and tearing it down. The metal from jj13's camgear will have drained into the sump with the splash oiling. His call if he wants to take the risk and just replace the gear.

Al

Last edited by RV7 To Go : 03-06-2018 at 08:58 AM.
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  #10  
Old 03-06-2018, 05:31 AM
Michael Henning Michael Henning is offline
 
Join Date: Jun 2011
Location: Nashua, NH
Posts: 546
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Removing the engine doesn?t take that long. All of the work is getting stuff set up the first time. I do t know a out accessory ase, if it can?t be that hard to open up.
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