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Low fuel Pressure Root Cause maybe

jj13

Active Member
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_CoALWDaYxOngywuOlrDkMaiadZ_muyw
 
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.
 
Rebuild

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
 
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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.
 
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 ;^)
 
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.
 
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.
 
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.
 
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
 
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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.
 
Your pic makes it difficult to see how much metal has worn off. It honestly doesn't look like much to me, but I would need a better look. You cannot assume that your lack of pressure is from a worn lobe unless you can see the wear, or better, measure the lobe and compare to spec. I would start there. You should be able to get a small calipar or mic in there.

If the lobe is worn down, you will have to assess the risk or continuing to run. Metal flowing through the oil is not as uncommon as you might think. The damage typically found was outlined in a previous post. None of those issues create a short term risk (assuming oil pressures haven't exhibited a downward trend). However, metal impregnated in the bearings will likely cause excessive scoring of the journals over the life of the engine. That will require more work on the crank at rebuild. That scoring could be enough to scrap the crank ($5K problem) if the scoring goes beyond the 6 under journal size. Unfortunately, unlike an auto engine, you cannot inspect the bearings without a full tear down.

You can't eliminate the pump without removing or securing the plunger in a position that won't make contact with the lobe. You could however gut an old pump and just leave the main arm spring in place. You don't want that plunger bouncing into the lobe millions of times. It creates a risk of things ripping apart. It is possible that gravity will keep the plunger down, but wouldn't want to count on that. Many have removed their pumps for EFI, so I expect their is real data on the risk involved here.

Larry
 
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Back to doing the full repair

Well after some thought and realizing that adding the additional electric fuel pump with re-pluming will take considerable time. I've decided to pull the engine and remove the accessory case and replace the gear and plunger so that I can continue to use the mechanical fuel pump. I'll learn more about the engine which I should do anyway.

Areo Sport Power said that Superior likely did not heat treat the top of the Fuel plunger. They also said that the metal from the cam and fuel plunger was unlikely to cause any damage because the filter would have picked up the fragments before pumping the oil through the bearings. Also this was happening over an extended period of time so the volume was very low per oil change. I never saw or detected anything in the filters. They also said the engine makes some metal anyway and this issue did not significantly increase that amount. Anyway it's not worth it to me to do a teardown, I see very little risk especially from catastrophic failure just doing the repair. Yes maybe the life of the engine will be reduced.

I really appreciate all the feedback and ideas, all of it help me make what I think is the right decision, or at least an informed decision.

Now I get to do my condition inspection early while it's still cool here in Atlanta...not a bad thing:)

Thank you
 
Well after some thought and realizing that adding the additional electric fuel pump with re-pluming will take considerable time. I've decided to pull the engine and remove the accessory case and replace the gear and plunger so that I can continue to use the mechanical fuel pump. I'll learn more about the engine which I should do anyway.

Areo Sport Power said that Superior likely did not heat treat the top of the Fuel plunger. They also said that the metal from the cam and fuel plunger was unlikely to cause any damage because the filter would have picked up the fragments before pumping the oil through the bearings. Also this was happening over an extended period of time so the volume was very low per oil change. I never saw or detected anything in the filters. They also said the engine makes some metal anyway and this issue did not significantly increase that amount. Anyway it's not worth it to me to do a teardown, I see very little risk especially from catastrophic failure just doing the repair. Yes maybe the life of the engine will be reduced.

I really appreciate all the feedback and ideas, all of it help me make what I think is the right decision, or at least an informed decision.

Now I get to do my condition inspection early while it's still cool here in Atlanta...not a bad thing:)

Thank you

Have you not been sending in oil samples to a lab for analysis?
 
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