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Fuel Pump Issue
As several already are aware, I had some fuel flow issues on my first flight. At the time, in the air, I wasn?t quite sure what the issue may have been. It was initially looking like a blocked fuel line. The symptom was that the fuel pressure dropped significantly, but came back up with the electric fuel pump turned on and switching the tanks. I promptly landed and started looking for the root cause.
1. The left and right tank fuel flow (measured at the firewall, forward of the filter and pump) was 58 gallons/hour. Rules out a blockage aft of the firewall. 2. The fuel vents are not obstructed I ran the engine in a static test. Was getting about 20psi on the engine fuel pump and about 26psi with the electric fuel pump enabled. Since this is all within specifications, this is the worst of all the scenarios. No root cause and everything seems to be working as designed. This morning I flew for about an hour on flight #2. When I turned off the electric fuel pump, fuel pressure started to immediately drop. I let it drop to about 10psi before I re-engaged the electric fuel pump. With the electric fuel pump running, I was getting 26psi. I repeated this scenario multiple times on both fuel tanks during the flight. Results were pretty consistent. It?s looking like I may have a bad fuel pump on this 1 SNEW YIO-540-D4A5. I plan on giving Lycoming a call in the morning. My questions is there any other scenarios that I?m overlooking that may yield similar symptoms? Thanks, bob |
Bob---any evidence of fuel being dumped overboard?
Tom |
Sounds like the engine driven pump or an obstruction between it and the firewall however I assume when you checked fuel flow you disconnected at the engine driven fuel pump. if so I would start with changing the engine driven pump.
My fuel pressure readings at cruise (electric pump off) stay around 23 psi. I also assume you made full power on take off and your temps are ok. If there was a flow restriction on take off you would also see it quickly in the CHT temps. If the only time the pressure falls is when you turn off the electric pump then I would again bet on the mechanical engine driven pump. Hope you all goes well. Pat |
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Good question. I only did the top half the post flight inspection today. I'll take a look at the drain tomorrow night when I crawl underneath to inspect. bob |
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bob |
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Bob |
After shipping the data logs from my two flights and ground testing to Lycoming, they are recommending replacing my fuel pump. Naturally, I am just outside the warranty period.
They recommended a part #62B26931, which I can find that it is an approved substitute for the installed part, which is a LW15473. Anyone know what the difference may be? Bob |
My buddy had a similar fuel starvation issue on his IO-360 Cozy MKIV after the first condition inspection. Turned out that the AFP fuel filter screen insert we replaced with a new one from Aircraft Spruce had such a fine micron rating, the mechanical pump could not pull enough fuel through it during a full power climb out. It would drop below 9 psi and the engine would sputter until the boost pump was turned on. Superior even went so far as to send him a new mechanical pump under warranty. When that did not help, we pulled the old filter out of the trash and compared it to the replacement. We never noticed the difference in screening as the old filter was pulled out and tossed one day then replaced a couple days later. Cleaned the old one up and used it with no more fuel pressure problems. The electric boost pump had no problems pulling the fuel through the filter but the mechanical pump on its own could not do it on a high OAO full power climb out with the fine mesh filter. I hope the new pump cures your problems.
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Bob
The only thing I found was a Lycoming service letter which allows the use of the fuel pump P/N 62B26931. I don't see it anywhere. AERO in stock has the Lycoming LW 15473 Pump as does ACS. http://www.aeroinstock.com/products/...h=TFcxNTQ3Mw== http://www.aircraftspruce.com/catalo...elpumpLYC2.php It's a shame they will not replace the pump with only 1 hour in service. Does not say much about Lycoming customer service..... |
So, your buddy has an extra one that he can send to Bob! I like that customer service from Superior.
Lycoming, on the other hand... Man, bob! that's a bummer. Plus, it's a pain to change on a mounted engine. Sorry you gotta put up with that after just getting flying. Hope you can get it going again quickly. |
Bob,
First, congrats on flight testing. 2nd, could you share some of the pressure vs time data? Just because the high pressure electric pump can provide the fuel, (you have 2 sources of data, 58 GPH, and consistent 26 psi) does not mean there is not a suction leak or high restriction resulting in cavitation somewhere between the mechanical pump and the tank. It seems too obvious just to blame the mech pump. Where do you have filters and screens? I think those would be the fist place to start diagnostics. A new system is the most contaminated it will ever be. Back to data, you said the pressure decreased not dropped when switching the electric pump off. It takes a little time to build up vapor in the line if either a suction leak or just high suction and vaporization. Just wondering - -did you do any kind of fuel system, from tank to firewall pressure test to check for leaks? I was thinking about an air pressure test with a leak down type of test for small leaks. Maybe suction? |
I'm going to make a call to Lycoming again in the morning to debate the warranty status.
I've found that Tempest has a equivalent model for about $100 less. Does anyone have any experience with them or can comment on their quality? Thanks, Bob |
Bob,
I know the quick solution is to replace the pump, but I too am thinking you have a restriction or leak in the system between the mechanical pump and the fuel selector. I know you replaced the aluminum lines with flex line. I would pull all the lines and verify that there are no restrictions or flaps inside the hose. Prior to that I would pressurize the entire system from the fuel pump inlet line to the tank, and do a leak down test. Just thinking out load...... |
Bob, any chance you have the Andair fuel pump or did you go with the stock one?
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Bob |
Level flight?
My fuel pressures drop in climb with just the mechanical pump (same during my transition training in the company -10), so I leave the boost pump on through most of the climb. You didn't really say, and I assume the pressure drop was in level flight, but if it was in a climb, it's pretty normal.
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Were your fuel tanks full as well? When I fill my tanks to the top and climb out for an extended period of time I will get a fuel pressure drop that will trigger an alarm. The second I level off and burn off some fuel it goes away. My hypothesis is that the fuel breather gets fuel in it and then the mechanical pump has to pump the the fuel from the tanks with a "plugged" breather hose that is filled with fuel. It won't do it if the tanks are not full. |
Hmm
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Ours runs 28-29 psi in cruise and 19-20 psi during full fuel climb without boost pump. If it went below 15 psi or ran rough/lean then I would turn it on.
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purge valve bypass
Bob.
Just thought...but if you had purge valve bypassing slightly... when you turn on electric pump on is it possible it increased flow to raise pressure even with purge valve bypassing? Again just thought I had. |
Bob, I looked at the data (nice data service, BTW) and it did not appear that the low pressure occurred on the last ground run where you were testing various combinations. It looked like it was never lower than 23 when the boost pump was off and the rpm was even up to near 2700. If this is correct, then it indicates (to me) that the mechanical pump is functioning properly even at high fuel flows. And, that the issue of dropping pressure is due to higher suction from angle of attack and lower absolute ambient pressure from altitude resulting in fuel vaporizing due to the low pressure to the point that the mech pump can not keep up.
So, unless the "community" as some absolute suction pressure target for a clean system to check against. The only option seems to be to clean and check screens and filters, and verify there is no tiny leak that is allowing air into the system. It is still possible a tiny leak could be there but has not reduced the pumping effectiveness enough on the ground to cause pressure drop. Clearly this situation needs to be addressed as it will only occur more easily during hot fuel conditions. I will add more if my brain lets me. Curiosity, where did you place your red cube in the system? |
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just a thought--
years ago in automotive, we would get low, or very little fuel pressure from some 350 chevrolet engines that had a return line at the pump. Blocking off the return, solved all of those issues.
Granted, we are dealing with a different situation, it's similar to what Bob is experiencing. I know that he has inspected all the hoses from the firewall aft to the tanks, and found no issues. I know that he has looked at every component, its location, and how it all interacts with each other. This one is puzzling. |
I just received this from Lycoming. At the moment, they are following the legal technicality of the warranty term. Which means that the fuel pump, while it may be DOA, the repair is on me. I'm still attempting to convince them that it should be a warranty repair.
--------- Bob, Thank you for the information. It appears that the engine driven fuel pump needs replaced. The part number of the fuel pump is 62B26931. I downloaded this issue in our system, the reference number is 2567. Please order the part through an authorized Lycoming Distributor. http://www.lycoming.com/Lycoming/PRODUCTS/DistributorLocator.aspx Thank you, |
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Bob,
What's the chance of sending the pump to the manufacturer for evaluation? Bill |
Same here
Your numbers look just like mine!
After all this it's probably too late to convince you that nothing is wrong with your fuel pump. |
I will be very surprised if its a mechanical fuel pump issue.
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We'll see what the real root cause is over the next few days. I'll be checking the filter screens as well as replacing the fuel pump.
Lycoming has authorized a warranty repair. bob |
We suffered from fluctuating fuel pressure on our RV 10. After replacing the engine driven pump twice, I installed cooling shroud and that was the last of the problems. Rock steady the past 300 hours.
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All is finally well!
I ended up replacing the fuel pump and added a cooling shroud and blast tube to keep the pump cool. The pump never dropped bellow 22psi during the hour long test flight. Now I can start resuming normal Phase I flight testing. Thanks to Steve Beaver for assisting with the pump installation I also inspected the fuel filter and it was perfectly clean. |
Bob,
Congrats on finding the problem! Did you take any photos of the shroud installation? It sounds like a good idea |
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I had to enlarge several of the openings to fit the lw-15473 pump. Apparently one size doesn't fit all. |
That's great news Bob!
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Outstanding!!!!!!!Now---go and enjoy phase 1--
Tom |
In deed good news.
I had to replace my FP and add a blast tube also. Since I did both at the same time I'll never know which fix really worked. My guess is the blast tube. I did not add the best shield, just a blast tube on the suction side of the engine mounted FP. |
Thanks for the update, and congratulations on your diagnostics and success in getting the problem solved.
I am now convinced that we, the AB community, need an engine installation guide book with some definitive specifications to allow every builder to test an installation for acceptable operation. This can provide data to understand if it is an assembly or design problem. We, are a huge group of people and have the resources to gather data one piece at a time. This can help us to generate an engine installation audit of temperatures and pressures that will ensure proper operation over a wide range of operating conditions. Like an EAA "standard" . Maybe these already exist, if so someone please let me know what and where they can be accessed. We should be able to completely eliminate installation short comings for all builds regardless of their technical knowledge. |
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IIRC, somewhere in the FWF plans from Vans they recommended a shroud for the engine driven fuel pump on the RV-10 due to heat so I went ahead and put one on mine before hanging the engine. Since I plan on running mogas in one of my tanks I wanted to keep the fuel delivery as cool as possible anyway.
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