Geico266

Geico266

Well Known Member
Normal / slightly aggressive climb out from 1,500 msl, 85F day to 6,500 msl. Engine temps normal, engine starts to sputter and I notice fuel pressure is 4 PSI.:eek: I flip on the boost pump and life is good with 27 PSI.

After landing without incident I let the plane cool down and fired it up again and the fuel pump seemed to work fine with 27 PSI.

Standard Vans set up with IO-540-D with mechanical pump fuel pump & electric boost pump back up. However, there is no blast tube to the fuel pump, and only one set of louvers on the cowel.

My plan of action is;

1. Replace the fuel pump.
2. Install a blast tube to the fuel pump.
3. Install a second set of louvers in the bottom of the cowel.

Any thoughts or other ideas?

Thanks in advance for your input, I always greatly appreciate it.
 
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Two things

Either pump is somehow not keeping up with demand (blockage, hole in diaphram etc)...Or its vapour lock

Frank
 
frankh said:
Either pump is somehow not keeping up with demand (blockage, hole in diaphram etc)...Or its vapour lock

Frank
Click to expand...

Vapour lock in the air? I was burning 12-14 GPH. Would not the cool fuel keep it from doing that? Wouldn't vapour lock stop the flow all togeather? It still had 4-8 PSI. This was the 1st run of the day also.

Frank, I'm not arguing with you, I'm just trying to figure it out. I think you are right, but everyone I've talked to locally doesn't think it was vapour lock.
 
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I agree with frankh--this is classic vapor lock.

I doubt there is anything wrong with your fuel pump.

Most of my flying is behind six-cylinder TCM engines in store-bought airplanes, but it's not uncommon for the POH to recommend boost pump continuously in the climb, and continuously in high-temp cruise or high-altitude cruise.

My RV didn't run well at all in hot temps until I added a blast tube.

There is a cooling shroud available here for Lycoming fuel pumps under "products."

As a temporary fix, take the fresh air supply off of your heat muff and direct it towards the fuel pump,
 
The vapor lock gremlin strikes you on the suction side of the pump - high flow rates aggravate this. More nose-up attitude aggravates it as well, since the pump has to pull the fuel a little more up-hill to the suction side of the pump, further lowering the suction side pressure. The air temp may have been 85, but what was the fuel temp? Were the tanks baking in the sun before takeoff? Higher fuel temps give higher vapor pressure, leading to easier vapor lock.

I don't believe I'd pull the pump if I were you - I think I might install a suction-side pressure gauge and go out and try to duplicate those flight conditions and read that suction-side pressure - I think that will tell your story.

A blast tube onto the fuel pump is never a bad idea.
 
I vote vapor lock too

I flew an RV-6A that presented the same symptoms once on a hot day. The owner told me that it stopped happening once he put a blast tube on the fuel pump. That's pretty anecdotal evidence, but it might be worth something.

Since I have my fuel pump off the engine right now anyway, I think I'll take the opportunity to install one of those cooling shrouds while I have easier access. Thanks for the timely reminder and good luck finding the source of the problem.

mcb
 
Sometimes (depending on installation plumbing to sender) a tell-tale indication of bubbles in the line to the engine driven pump is fluctuating low pressure on the fuel pressure gauge, not just low pressure.

It's also possible to have a fuel line leak that lets air into the fuel line prior to the engine driven pump. The leak may or may not present itself when positive pressure is applied via the electric pump operation.

Was the acft sitting in the sun all day heating the fuel in the tanks? What fuel, 100LL, Mogas, Auto fuel with ethanol?

How old and how many hours on the engine driven pump?

I agree, first thought is classic vapor lock..... but many times first thoughts are wrong.
 
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The symptoms support a vapor lock at or near the inlet to the engine driven pump. That pump will not suck vapor. You turned on the electric pump and it pushed the fuel through and the engine came back to life. Same thing would happen if the mechanical pump failed but it worked OK later on the ground. Fuel pumps don't fix themselves.

OAT and fuel temp were on the warm side, but the real culprit is heat at the firewall where the unpressurized fuel comes through. It is a hot area (you could install a simple OAT sensor in the area to see how hot it is) and it is a low fuel pressure area because the mechanical pump is sucking fuel from the tank at a good rate.

The six banger is a heat generator, more HP means more heat, I will bet more so than the six banger Subaru. I had a temp gage in the area and it convinced me to move all the fuel pumps aft of the firewall. Fuel pressure going forward at 30 psi will not lock up, not even mogas. But it will at zero pressure when it gets warmed up forward of the firewall on warm days. Your exhaust pipes are probably running at 400-500F (considering 1100-1200 EGT) not far from the fuel pump, that is a warm area for sure.

Just my 2 cents worth. I would go with the pump cooling shroud and keep my finger near the electric pump switch on warm days. :)
 
Argument?

Geico266 said:
Vapour lock in the air? I was burning 12-14 GPH. Would not the cool fuel keep it from doing that? Wouldn't vapour lock stop the flow all togeather? It still had 4-8 PSI. This was the 1st run of the day also.

Frank, I'm not arguing with you, I'm just trying to figure it out. I think you are right, but everyone I've talked to locally doesn't think it was vapour lock.
Click to expand...


Hey Geico,

You can argue with me all you want...Its also called healthy debate and I have no problem in being wrong and am very happy add to the mix of ideas...A good brainstorming never hurt anyone...:)

Let us know what you find.

Chers

Frank
 
Great info guys thanks.

I have been running 91 Octane mogas & 100LL mix, it should be around 50-50. The pump has 200 hours on it and is 2 years old. The problem showed up after I leveled off and was deceasing airspeed to do some stalls & slow flight so I'm leaning towards vapour lock also.

Someone asked what the temp of the fuel was. It was 82F. I actually took the temp of it after I landed. The plane was in a hanger all day, only in the sun during start up and flight.

If I wanted to test things one at a time I would, but I just don't want to take a chance so I'm replacing the fuel pump, installing a fuel pump shroud (a hanger buddy gave me one) & blast tubes and install additional louvers. Over kill maybe, but..............
 
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Geico266 said:
Can you get by with removing just the outside shell? The "covering" with the inlet & outlet only?
Click to expand...

I don't see why not.

My muff comes off completely in two pieces so it wasn't an issue for me.

In my installation, I had terrible "surging" at idle in hot weather and some surging in the pattern. I talked to a bunch of people and tried several things, including replacing the spring in the "spider" to increase fuel pressure in the metal lines--nothing changed the problem significantly.

Moving the 2-inch SCAT tube to the fuel pump solved the problem completely, even on the ground (which surprised me).

Since then, I have been sprinkling these temp sensors around the engine compartment to see what need more cooling. My CHTs and oil temp were good from day one, but I was surprised to see how hot some of the accessories were getting. I am always tweaking blast tubes to maximize the life of everything.
 
360 vs. 540?

Is this problem limited to the 540 installation? Anybody ever heard of similar issue with a 360?
 
not exactly the same, but...

I was trying to decide if I should install a shroud so I place two temp probes on either side of the fuel pump. One on the side that the blast tube was pointed at and one on the other side. I saw very little temp difference between the two probes.

I think that the heat would be more likely to come through any unshielded fuel line.

Has anyone installed some way to run cooling air along the fuel line?

Kent
 
Well, the blast tube fixed the problem, kinda. The tempurature was 85F today (same as when the problem started) and I did the same climb out to 6,500 MLS and leveled off. The fuel pressure started to drop, but this time it only went to 10 PSI and as I gained airspeed (and the blast tube cooled the fuel pump) the pressure came back up to 24 PSI. If I leave the boost pump on pressure stays at 26 PSI.

I highly recommend all RV's have a blast tube cooling the mechanical fuel pump just to be on the safe side.
 
Geico266 said:
Well, the blast tube fixed the problem, kinda. The tempurature was 85F today (same as when the problem started) and I did the same climb out to 6,500 MLS and leveled off. The fuel pressure started to drop, but this time it only went to 10 PSI and as I gained airspeed (and the blast tube cooled the fuel pump) the pressure came back up to 24 PSI. If I leave the boost pump on pressure stays at 26 PSI.

I highly recommend all RV's have a blast tube cooling the mechanical fuel pump just to be on the safe side.
Click to expand...

Thanks for the followup.

I might suggest adding a line to your POH about leaving the boost pump on for climb if OAT is above say 70 degrees. This is how Cirrus (among other store-bought airplanes) manages this issue.

I know everybody says this is normal, and that we should live with the surging idle in hot temps, but I find that really unsatisfying. With the latitude our "experimental" certification gives us I hope somebody figures out a way to fix it definitively.

A lot of us were driving in the 1970s, and may have forgotten that this was a problem with new cars at the time, at least in Southeastern summers. The early pollution controls and early automotive fuel injections meant some relatively expensive cars were difficult or impossible to start when hot, and would occasionally stumble and quit under load (like pulling a boat up a ramp)
 
flyeyes said:
Thanks for the followup.

. With the latitude our "experimental" certification gives us I hope somebody figures out a way to fix it definitively.

)
Click to expand...

I already have!...:)...Put electric fuel pumps in the wingroots..Been running 300 hours this way...Vapour lock, stumbling engine?..Whats that?

Frank
 
Thanks

Personally I would place the mechanical fuel pump in the same place as the vacuum pump...Namely the trash can...:)

Electrical stuff is just so reliable these days that we don't have to stick with 1940's technology.

Frank
 
frankh said:
I already have!...:)...Put electric fuel pumps in the wingroots..Been running 300 hours this way...Vapour lock, stumbling engine?..Whats that?

Frank
Click to expand...

That's where mine will be going...it just makes good sense from the hydraulic perspective.
 
Noah said:
Is this problem limited to the 540 installation? Anybody ever heard of similar issue with a 360?
Click to expand...

Larry has a -10, I am assuming he is talking about it, due to the 540 comment.

The -10 has a heater valve design where the hot air comming off the muffs gets dumped right in the fuel pump area, when you are not using cabin heat.

The heat shields from Show Planes, and Aircraft Spruce appear to be the same unit, either should make a major improvement it the local environment the fuel pump lives in.
 
Pumps in tanks

I wonder if it might be good to take Frank's solution a step farther and put electrical pumps in the tanks like modern cars do? Then you have totally eliminated any possibility of vapor lock. Most new fuel injected cars now use tank pumps that have proven very reliable and safe. Probably not really necessary since the wing root is only two connections and a few inches from the tank, but it is a thought.:confused:
 
I thought about that as well - but dismissed it for a couple of reasons. One is the obvious challenge of changing the pump should it ever fail. You've got the additional sealing challenge for power wires running in and out of the tank, and you're taking up additional volume (granted, not much) in the tank, but I would consider the necessity of hard-mounting the pump in the tank as well. You've got more options for hard-mounts externally than you do internally (remember, this install needs to withstand several G's).

The only real reason to extend the clean hydraulic scenario to the point of putting the pump in the tank is to further decrease the pressure drop between fuel supply and pump intake. For the very short runs we are talking about, it's quite easy to run large-bore fuel lines for minimal pressure loss even at high flow, and take advantage of the low-temperature environment of the wing root with its available space and choice of hard-mount options with easy wiring access. Basically, by moving the fuel pump from the FWF area to the wing root, you've eliminated 98% of your vapor lock risk - you have to balance the effort required to remove the last 2% against the gains received. In my analysis, you're past the point of diminishing returns with in-tank pumps. My analysis only - YMMV.
 
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Yup

Thats pretty much where I got to..

The ugly factor of changing out an in-tank pump was just too big of an obstacle....Besides, I wanted it to work upside down..:)
 
I see merits of your system (wing root elec pumps). As an operational practice I do not run a tank dry. That gives me the option of switching tanks if a tank fails to feed. I would be even more inclined to not run a tank dry with your installation.

Hey if fuel stoppage can happen to a 777 and they still can't figure out (or admit) what happened, a fuel stoppage issue could happen to a RV.
 
If you place a fuel pump in the wingroot, you will also need to install a 74 micron filter before the pump if you are using a FACIT pump, per instructions.

And if you do install a filter, you will need a shut off valve before the filter so you can service the filter without the tank being empty. That is a LOT OF STUFF in a small area.

How about if you install two filters, two pumps and two check valves side by side just after the fuel selector valve? Easy to maintain and will solve 97.8% of your fuel lock problems if you get rid of the gascolator and the engine mounted fuel pump and run the fuel line from the firewall direct to the carb.
 
You could go.....

Tank, fuel shutoff, filter, electric pump, check valve, carb

both L/R lines T together after the check valves, before the carb.

If you trusted the check valves you could get by with no selector and run both pumps on and feed both tanks at the same time. A dry tank would not feed air because the fuel pressure of the remaining tank would keep the check valve closed. Of course a slightly higher fuel pressure from one pump would lead to an imbalance in which case you could run one pump at a time to balance fuel.
 
gasman said:
And if you do install a filter, you will need a shut off valve before the filter so you can service the filter without the tank being empty. That is a LOT OF STUFF in a small area.
Click to expand...

Could we just use draining valve to do the job? As you know this, you could always get your tanks quite empty before doing maintenance and if you need to check your valve with most fuel on board, you could use drain valve to remove extra...?

Probably easier than having another valve there...
 
asav8tor said:
You could go.....

Tank, fuel shutoff, filter, electric pump, check valve, carb

both L/R lines T together after the check valves, before the carb.

If you trusted the check valves you could get by with no selector and run both pumps on and feed both tanks at the same time. A dry tank would not feed air because the fuel pressure of the remaining tank would keep the check valve closed. Of course a slightly higher fuel pressure from one pump would lead to an imbalance in which case you could run one pump at a time to balance fuel.
Click to expand...

I don't think I would be comfortable running one of my pumps dry for any period of time. The pump itself (and in some cases the motor, with in-tank pumps) rely on fuel for lubrication and cooling. Dry run times would cook the pump. Having only one pump operational at a time ensures that you know IMMEDIATELY when that pump runs dry.
 
OK

As I do this I probably ought to chime in here.

1) Never run a pump dry, as firstly it doesn't do the pump any good and secondly because you now have a single point of failure...I.e the other pump. In practice I have never sucked a tank below 4 gallons, but I would go to 2 gallons if I was close to an airport.

2) My system does no use a selector valve..It is neither necessary or desirable..You want to be able to run both pumps for TO and landing...You can't do this with a selector valve..Well you can but it is a layer of complication you could do without for zero benefit.

3) A valve ahead of the pump is not needed in practice...I have change the filter with a full tank and spilled barely a teaspoon...

4) For the carb'd system a filter is really not necessary ahead of the pumps..Those FAcets are prety solid ...I probably would put a filter in there because there is plenty of room but they will be fine without...The FI'd system definately needs the filter though.


Se my pictures for the install.
 
asav8tor said:
You could go.....

Tank, fuel shutoff, filter, electric pump, check valve, carb

both L/R lines T together after the check valves, before the carb.

If you trusted the check valves you could get by with no selector and run both pumps on and feed both tanks at the same time. A dry tank would not feed air because the fuel pressure of the remaining tank would keep the check valve closed. Of course a slightly higher fuel pressure from one pump would lead to an imbalance in which case you could run one pump at a time to balance fuel.
Click to expand...


Yes at cruise I run one pump at a time...No seletor valve!...This will bite you one day for sure!
 
Switching Tanks

asav8tor said:
I see merits of your system (wing root elec pumps). As an operational practice I do not run a tank dry. That gives me the option of switching tanks if a tank fails to feed. I would be even more inclined to not run a tank dry with your installation.

Hey if fuel stoppage can happen to a 777 and they still can't figure out (or admit) what happened, a fuel stoppage issue could happen to a RV.
Click to expand...

Just a clarification...But I need to make sure you guys understand what "switching tanks" means.

In my system this means both pumps are turned on...Then the not required pump is turned off. This is partly why the selector valve is undesirable..I.e you will have to coordinate the valve with the running pump and it prevents you from feeding the engine simulatneously from both tanks.

The beauty of the system is its simplicity in use, you control the thing with two switches, nothing else to get confused with.

Both for TO/landing, one pump in cruise...Oh and forget about VL, its a non issue.
 
You will still need a master fuel shutoff between the Tee where both fuel lines come together and the firewall, to be able to shut off the fuel flow in event of an engine fire or off-airport landing. Where did you put yours at Frank?

Sidenote - I think I would like to have a fuel pressure switch between the pump and the checkvalve/Tee assembly wired to an LED on the panel immediately above the corresponding switch. This lets you see at a glance whether that pump is operational when you flip the switch, and gives you an indicator to confirm a suspected pump failure in the case of power loss.
 
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frankh said:
The beauty of the system is its simplicity in use, you control the thing with two switches, nothing else to get confused with.

Both for TO/landing, one pump in cruise...Oh and forget about VL, its a non issue.
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Does your power lead for your fuel pumps connect direct to the battery?
You would not want to shut the fuel off if you had to turn off the master.....:eek:
 
gasman said:
Does your power lead for your fuel pumps connect direct to the battery?
You would not want to shut the fuel off if you had to turn off the master.....:eek:
Click to expand...

That's what the E-buss is for. You should be able to draw power from either buss for the flight-critical items.
 
Exactly

airguy said:
That's what the E-buss is for. You should be able to draw power from either buss for the flight-critical items.
Click to expand...

The Battery buss is the one wired directly to the battery. Thats where the pumps are wired to, via dedicated wiring, fuses and switches.

There are no shared components except for the battery and buss istself.
 
As a side note, I had drilled a small hole in the back side of the fuel vent lines. We talked about this helping if a bug plugged the hole you would be able to continue to vent the tank. However, the added hole in the vent tube may have decreased pressure in the tank and added to low pressure and vapor locking at the mechanical pump. I closed the holes and it did help with keeping pressure up before the mechanical pump, but I had already made other fixes so I do not know if it was a primary cause. Just a thought, IMHO I would not add the holes to the vent line. Vans has them designed this way for a reason, and the chances of plugging the vent line and collapsing the tank is very small.

With all of the "fixes"; blast tube, "hot tunnel" sealing, opening up louvers a tad, adding a "summer time" air baffle to the cowel opening to aid in air evacuation I have had no more VL issues even with the boost pump off.

The loss of fuel pressure was certainly not a bad fuel pump. It has been working just fine ever since.
 
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Vapor lock!

Check you gas caps. Non-sealing gas caps allow low pressure to form in the tanks. Pump has to work harder to suck fuel and on a hot day..... VAPOR LOCK!!

Make sure your tank vents are adding slight positive venting pressure to your tanks. Bad vent system = VAPOR LOCK!!

Many fuel injected planes need to operate at hot/high altitude with the boost pump on for this and other reasons.


Best wishes, Bob (in always hot Florida)
 
DON'T TELL PIPER...

Rocketboy said:
Vapor lock!

Check you gas caps. Non-sealing gas caps allow low pressure to form in the tanks. Pump has to work harder to suck fuel and on a hot day..... VAPOR LOCK!!

Make sure your tank vents are adding slight positive venting pressure to your tanks. Bad vent system = VAPOR LOCK!!
Click to expand...

DON'T TELL PIPER THAT!!

All PA28 series Pipers have vented gas caps, and also have vents for the tanks in the air stream.........:cool:
 
FRANKH

FrankH,
Can you help me by suggesting a fuel set up like you talk about for my Lancair?


Any discussion about replumbing a Lancair needs to be taken to private email. Even though Lancairs are fine aircraft, this is a forum dedicated to RV aircraft only.

Thank you,

S. Buchanan, moderator
 
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Could this be my problem, too?

I don't meant to re-direct this thread, but I can't resist inquiring about my idle issues. I have noticed recently that the IO-360 in my -4 runs rough at idle. This seems to occur only on restart in hot weather. For the first flight of the day, everything is fine. If I land, shut-down and re-start, the engine runs rough at low power, but is fine at higher power settings. I have not attempted to resolve the rough idle by turning on the boost pump. I do not have a blast tube on the mechanical pump. Could my mechanical fuel pump be too hot on the ground? Everyone's input is most appreciated.
 
NOT Vapour lock

Dean Pichon said:
I don't meant to re-direct this thread, but I can't resist inquiring about my idle issues. I have noticed recently that the IO-360 in my -4 runs rough at idle. This seems to occur only on restart in hot weather. For the first flight of the day, everything is fine. If I land, shut-down and re-start, the engine runs rough at low power, but is fine at higher power settings. I have not attempted to resolve the rough idle by turning on the boost pump. I do not have a blast tube on the mechanical pump. Could my mechanical fuel pump be too hot on the ground? Everyone's input is most appreciated.
Click to expand...

What I believe you have is heating of the injector lines above the engine...Mine does the same..This is not VL however as this describes boiling at the inlet to the mechanical fuel pump and is usually associated with high flow..This is why it is a VERY bad thing because it can happen in a hot day at takeoff...

But what you have is low flow..where the tiny amount of fuel is going thought the 1/8th lines that have been heat soaked by the hot engine sitting on the ramp.

If it goes away at full power then that is what you have.

If it bothers you you could try insulating those lines although I am advised this will alter the natural exitation frequency (vibration) of those SS lines...Personally I wouldn't have a problem doing that however.

Frank
 
frankh said:
What I believe you have is heating of the injector lines above the engine...Mine does the same..This is not VL however as this describes boiling at the inlet to the mechanical fuel pump and is usually associated with high flow..This is why it is a VERY bad thing because it can happen in a hot day at takeoff...

But what you have is low flow..where the tiny amount of fuel is going thought the 1/8th lines that have been heat soaked by the hot engine sitting on the ramp.

If it goes away at full power then that is what you have.

If it bothers you you could try insulating those lines although I am advised this will alter the natural exitation frequency (vibration) of those SS lines...Personally I wouldn't have a problem doing that however.

Frank
Click to expand...

Interesting. I installed, but rarely use, the purge valve feature that came with my AP fuel injection system. Do you believe running cool fuel through the system (albeit not through the fuel injection lines) would help/resolve the issue?
 
Yes it does

Dean Pichon said:
Interesting. I installed, but rarely use, the purge valve feature that came with my AP fuel injection system. Do you believe running cool fuel through the system (albeit not through the fuel injection lines) would help/resolve the issue?
Click to expand...


Well at least the AFP purge valve (I have one too) certainly helps with the hot start issue. Now as you say the fuel in the SS lines is not purged but certainly giving the rest of the system a good flush before start certainly can't hurt as this will make sure the fuel is somewhat cooler before it enters the SS lines.

I would also encorage leaning out the motor as far as possible when taxiing..even though it will make the rough running worse...Better to have ar rough idle than a fouled plug on takeoff however.

Generally this problem is more of a nusance than a safety issue however

Frank
 
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