Fuel Pump Help

I have about 110 hours on my RV-10 with a Van's factory new YIO-540 engine. The plane has the standard Van's FWF setup. At about 100 hours, I turned the electric pump off at 1000 ft during climbout, and at 2000 ft, received a low fuel pressure warning. I turned on the electric pump and the pressure jumped back to normal immediately. I then turned the electric pump off, and had no issues for the next 10 hours of flying.

Last Friday, I flew the familiy to Florida and had the same issue at takeoff. Decided to continue the flight to North Carolina with no additional issues. When taking off from NC, it did the same thing again, but this time, it repeated 3 or 4 times for the first hour of the flight. It then stopped for the next 1.5 hours. The last time it did this, I was right over an airport and decided to see what would happen if I did not turn on the electric pump. The pressure (normally at 25 psi) went down to about 12 psi, and then recovered back to 25 within a second or two without the electric pump.

So for all you engine experts out there, any suggestions for troubleshooting? I don't think it is a bad sensor, since the pressure responds immediately to the electric pump. One other thought would be the pressure relief valve opening and dumping fuel, but I don't know why the electric fuel pump would fix this issue. I would also think that any type of blockage would not be solved with the electric fuel pump. This leaves failure of the engine fuel pump, but I'm surprised the pump would fail the way this one seems to be failing. Any thoughts or ideas would be greatly appreciated.

Aaron

You may want to check your fuel filter screen if you have an AFP set-up. We had the exact same issue with the Cozy MKIV after its first condition inspection when we changed out the SS screen with a new one. Exact same symptoms as you describe. Superior even foot the bill for a new mechanical pump (IO-360) and still no help. After close inspection of the AFP replacement filter,,,it was obvious that the screen micron was much finer than the original it replaced so we cleaned the old one and swapped it back and problem was solved. The mechanical pump just did not have the power to pull the fuel through the finer micron filter at cruise power. You may have other problems but you may want to look into this.

I'm certainly no expert, but there have been several -10's reporting this issue so your situation is not uncommon.

Basically, IMHO what happens is due to the angle of attack and after climb out the fuel close to the mechanical fuel pump is heated up and what you are seeing is the beginning of vapor lock. When you level out, increase speed and cool everything off the problem "goes away".

A couple of things that helped the -10's that I worked on were;
1. Replacing the mechanical fuel pump.
2. Adding a blast tube to the mechanical fuel pump.
3. Leaving the electric pump on until you reach alt and then add 10 mins.

Are you using avgas or mogas? Mogas will VL a tad sooner than 100LL.

Vapor lock crossed my mind, but it did not seem to fit the symptoms. First, I did not have this issue at all over the summer, with temps in Connecticut up near 100F. I was doing all kinds of hot starts, steep climbs, etc, during the flight testing with zero issues.

Second, it was 22F on Friday when we left Connecticut. The fuel was at that temp, and it happened almost right after takeoff when everything was still relatively cold. It also occured with 3 tanks of fuel from 2 different sources (all 100LL), so I doubt it is a fuel contamination issue.

Third, it happened for the 1st hour of flight on my last flight. It seems that any vapor lock issues would work themselves out long before that.

I suppose one possibility is that the fuel is heating in the tunnel. I am now using cockpit heat, which is keeping the tunnel pretty warm. Still, it doesn't seem that this should happen right after takeoff on a 22F day.

Aaron

I experienced the same...

...and after reading the Pelican's Perch articles decided that upon departure at high power settings, I really needed that electric fuel pump on to achieve high fuel flows. (I depart 120kts, 2600 RPM, 22 GPH). I keep it on until cruise altitude at which time it goes off and I begin leaning. The problem hasn't returned. I am intrigued with the post about the screen and will be checking that one soon.

Brian
N104BS RV-10
294 hours
Nashville, TN

The problem definitely seems to be worse at the high fuel flows, but during the last flight, it dropped twice while in cruise, leaned at 65% power (about 12.3 gph). I'll have to take a look at all the filters and screens to see if there is some partial blockage.

Aaron

Vapour lock

Those symptoms sound awfully like vapour lock.

The Mechanical pump is a poor soulution Hydraulically speaking..Sucking on warm fuel through any kind of restriction produces ripe conditions for VL.

VL can can happen at full power ( max heat max suck), but also at reduced power where the fuel flowrate has slowed significantly and the extra time spent in the pipe (cus the fuel is flowing more slowly) provides more time to warm the fuel closer to its boiling point.

Part of the answer is to never take off or land without the boost pump running.

Frank

I did fail to mention...

10builder said:

...and after reading the Pelican's Perch articles decided that upon departure at high power settings, I really needed that electric fuel pump on to achieve high fuel flows. (I depart 120kts, 2600 RPM, 22 GPH). I keep it on until cruise altitude at which time it goes off and I begin leaning. The problem hasn't returned. I am intrigued with the post about the screen and will be checking that one soon.

Brian
N104BS RV-10
294 hours
Nashville, TN

Click to expand...

...that I did install a blast tube to the mechanical fuel pump. As mentioned in this thread, that may also been the reason my problem disappeared.

YUP

In this case it was almost certainly vapour lock.

Frank

I've always suspected the hot air from the cabin heaters heats up the fuel system in this area of the engine compartment. The return air from the cabin heaters is very close to the fuel system and fuel pump. Climb out would be producing good heat with minimum airflow for cowl cooling. Just a thought.

This is the failure mode for a fuel pump going bad. I've seen them do the exact same thing even with just a few hours on them.

What type of instrument are you using to measure fuel pressure?

If you have an electronic sensor and electronic engine monitor, it sounds like you have a bad ground or bad intermittent connection.

I have seen many engine instrument errors that could be traced to a bad ground. If you are using the airframe as the ground path for the transducers, try running a dedicated ground wire for the transducers.

I believe this to be a VP problem in the line that runs to the sensor. In the standard installation the transducer is higher then the fuel pump. If conditions are such that the fuel drains down the hose and is replaced by a bubble of air it can give a low pressure reading. Typically this will happen after you have made a brief stop for fuel and then take off with a climb to altitude. I moved my sensor lower then the mechanical fuel pump and I have never had a repeat of this problem. It is mounted, by adel clamps, to the outside lower left engine mount tube. Using this method you do have to ground the unit if it does not have it's own source of grounding.

10builder said:

...and after reading the Pelican's Perch articles decided that upon departure at high power settings, I really needed that electric fuel pump on to achieve high fuel flows.

Click to expand...

Be a little careful here ... John Deakin was flying a Bonanza with a large Continental up front. The Contenental injection system works differently to the Lycoming/Bendix system - it needs high fuel pressure to get full fuel flow, and if fuel pressure is low there is a danger of running lean and a risk of detonation. The Bendix system uses fuel pressure as the controlling variable, and so as long as the mech pump exit pressure is at the required level (25psi I think), then switching on the elec pump will not increase fuel flow. I'm not saying don't use the electric pump, just that if your mech pump is working properly it will not increase the fuel flow with a Bendix/Precision/AFP injection system.

Pete

Here in Oz where it gets pretty warm..........guess what happens? Just as you have explained.

Vans have a shroud type of fuel pump cooler which helps greatly.

Our SOP is to leave the pump on, level out let the CHTs drop after leaning to LOP and pump off.

Now the thought o fthe bubles in the line to the sensor being the problem..........that could be true, but why did the shroud help then?

Do not stress too much though.....it is normal.

DB

Thanks every for the replies. I flew a 45 minute flight to Naples yesterday and returned today. On both flights, I kept the fuel pump on until reaching altitude and leaning, and had no issues. I also kept the cabin heat off. So at this point I'm pretty sure its vapor lock as a result of heating due to the heat in the tunnel when the cabin heat is on. I plan to keep a close eye on it however to make sure it is not the mechanical pump going bad.

I'll have to see if I can get the problem to repeat with cabin heat after returning to Connecticut.

Aaron

That is good news, you are on the right track.

Aaron, I may not have made myself clear, sorry. IMHO, the VL heat problem for the -10 comes from the heat generated from the cabin heaters on the engine side of the firewall, not in the cabin. If your -10 was built per plans the fuel supply that penetrates the firewall is directly in the way of the hot air bypassing the cabin heater valves. Take a look at it the next time you have the cowl off. Make sure you have fire sleeve protecting the fuel line, and add a blast tube to the fuel pump. It really does help.

Good luck, and keep us posted.

Just another idea - if it is tunnel heat as suggested by some.
Did you you follow Vans advise on reducing tunnel heat.
See http://www.vansaircraft.com/pdf/tunnel_temp.pdf