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engine quits on take-off!

dougknight

Well Known Member
I have a friend with a RV 6-A. We took off the other day headed for lunch and the engine quit on us during climb out:eek:. Since then we have been trying to isolate the problem without much success, thus I address the community for added input and suggestions. We are pretty sure the problem is with fuel delivery.

Ever since he purchased the plane he has noticed an INTERMITTANT fluctuation in the fuel pressure gauge between zero and seven psi. He has kept a very close eye on it and anytime psi has dropped near .5psi he turns the electric boost pump (facet) on and it quickley returns to 6-7psi and no problems. The day the engine quit on us we had just taken off with the electric boost pump on and once reaching 800-1000 feet he turned it off, we were talking and he became somewhat distracted and did not monitor the fuel flow gauge for the next minuet or two whence it ran out of fuel and got quiet very quickley. He has been very aware of the low pressure problem since he bought the plane and immediatley re-energized the electric boost pump within two seconds and the engine surged back to life. We immediatly turned 180 degrees and landed at our home field, de-cowled and started investigating.

Approximatly two weeks prior to this incident he bought and installed a factory new fuel pump thinking the old one was the culprit of the intemittant low pressure readings and was trying to get away from flying the airplane with his eyes glued to the fuel pressure gauge all the time. I doubt the problem is in the engine driven fuel pump simply due to the odds of two of them in a row being bad with the same intermittant symptoms.

The engine is an O-360 Lycoming carburated with a fixed pitch prop and dual slick mags. He bought the plane complete and flying some 50 hours of flight time ago. Total time on aircraft I am not sure of, however total time on this factory new certified engine is approx. 750 hrs (2nd engine since the build) my friend is the third owner. The fuel system looks pretty standard RV (I have a 9A and I am the builder) as tubing comes from each tank to a selector in front of and between the seats then to a facet electric pump which is located just below the pilots left leg midway between the knee and ankle. Once it leaves the facet pump it goes through the firewall and does an abrupt 90 degrees for about 3 inches into the gascolator which is mounted on the firewall, exits the gascolator via a straight fitting and enters the starboard side of the engine driven fuel pump via a 90 degree fitting. It then exits the port side of the fuel pump via vans supplied fitting which allows for two tubes to exit, the main fuel line to turn 90 degrees and dump directly into a 45 degree fitting into the carburator, the second smaller line goes to the firewall mounted transducer for the fuel pressure gauge. All lines are flexable factory made hoses and are firesleve protected engine side of the firewall. Each tank has air vents routed and located per plans, however there are no fuel return lines as would be for an injected engine as this is carburated. All firewall forward pipe to tube fittings are AN type Aluminium except the 45 degree fitting into the carburator which is steel (we just replaced the aluminum). Both the fuel pump and the gascolator have shrouds around them with blast tubes originating from the baffles to aid them in cooling. We originally thought it may be vaporization of fuel in the line just inches from the carburator as it passed within an inch of the exhaust pipe but we have since installed a heat shield, double firesleeved the line and moved it up and away (3") from the exhaust pipe. Test flew it and the fuel pressure was still dropping intermittantly when the electric fuel pump was off.

This low pressure drop occures most frequently after first engine start of the day or after the plane has been sitting for more than an hour. It seems to be fine during taxi and run up even with the electric pump off. Turn boost pump on and take off it is still fine but as soon as you turn the electric pump off at 1000 ft agl we see an immediate slow drop in fuel pressure from 7psi to .5psi. Turn the electric pump on and the pressure builds back up to 7psi... turn it off and it again starts a steady drop to .5psi. After about the third time of boosting pressure back up with the electric fuel pump then turning it back off after pressure builds back up it seems to hold pressure just fine for the duration of the flight with just the engine driven pump running.

We are stumped and wonder if anybody else has encounterd anything like this or has any ideas:confused:.

Sorry for the long post but I wanted to provide as much information as possible.

Thanks in advance

doug
 
Sounds like a classic case of "vapor lock". (Sidebar = I dislike the term "vapor lock" because it does not lock anything, but it is what everyone knows.) The clues are it happens on climb out after the second run of the day when the cowl FF is heat soaked. The fix is turning on the boost pump which pushes fuel below the fuel level instead of pulling it like the mechanical pump does. It is also happening now that the temps are warmer.

Fixes = Leave the boost pump on under 1,000' agl, when switching tanks, and 10 mins after climb out and level off. This will allow the airflow to cool off the engine and fuel pump area as airspeed increases. Add a blast tube to the intake side of the mechanical fuel pump, or install a fuel pump shroud. Put fire sleeve over all fuel lines and fittings. You want to keep the fuel as cool as possible. Make sure the facet pump is in good working order. ;)

JMHO and experience in dealing with same.

Do a search for more info.
 
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Any evidence of fuel leaks anywhere? Excessive fuel burn numbers? Checked the vent lines for blockage/bends/kinks? Possible vapor lock upstream of the mechanical pump due to fuel line routing?
 
7 psi seems low for the FACET pump. Mine shows 12 psi. Of course our(s) instruments maybe off calibration too...

what fuel is he using?

Does he have fuel flow? If so, what does it show?
 
"This low pressure drop occures most frequently after first engine start of the day"

Sounds like the engine driven pump is starving for fuel, the fact that it does it on the first run of the day before things heat up kinda rules out vapor lock.

I would start checking for blockages/obstructions from the engine driven pump back. You could have a plugged gascolator or a fuel line, check the fuel line for a rubber "flap" which can occur when fittings are installed and the rubber is cut inside the line, Van's had a recall of these lines years ago if I recall.
 
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Walt/Larry/Pat are pretty much right on. Given your explanation of events and the resultant behavior with the boost pump, it's highly likely that their explanation is the issue (that being some sort of vapor lock, either heat related, physical restriction related or leak related). 7psi is more than enough with the facet pump on a carb'd install, so I wouldn't worry about that.

There must be something up stream of the engine driven pump (perhaps between the boost pump and the engine driven pump) that is causing a blockage, or there is something else like a leak, etc...

Either way your friend either had two bad engine driven pump (not probable but possible), or there is a vapor lock issue. Is he running MOGAS or AVGAS?

My 2 cents as usual.

Cheers,
Stein
 
Cam lobe

Another thing to check is whether the lobe driving the fuel pump is worn to where you are getting suboptimal performance out of the fuel pump.
 
More info needed.

When this happens how much fuel is in the tanks? Do you notice a difference with full fuel versus low fuel? I think it is the nature of the animal, low wings high angle climb out the head pressure to the engine driven pump is low. I'm guessing if he were to leave the boost pump on until he levels off he would have no problem. I'm also going with others that the engine pump is weak. I have the same engine and same plane. I notice on climb, if I shut down the boost pump the pressure drops. Sometimes as low as .5 pounds. I never had a hickup from the engine though. As a test try two things. First full fuel and watch the pressure with the boost pump off on climb out at a safe altitude. Second, boost pump on till up at altitude and level off before shutting down the boost pump. See what pressures you are getting then.
 
since electric pump is pretty much pushing fuel and the problem doesn't occur when it's running, your mechanical pump may be pulling air into the system from somewhere between the tanks and the pump. check to make sure all your fuel fittings are tight and all seals in the selector and gascolator are good - you may be able to pull air from the problem area without leaking fuel.
 
Additionally, you could also check to see that there are no chances of a leak where air could enter the line (ie., a drain valve or B nut). For example, the scenario you describe has occured with a not completely seated gascolator drain valve on a piper cherokee. (Pitch up a little, and it sucks air - interrupts fuel flow - engine quits. Pitch back to level and the engine lights off again.)
 
I have possibly the identical fuel setup as you yet I have NEVER had the engine stop upon take-off. Never. Not once. Fuel pressure does drop at times but who cares?

I biased my RMI engine monitor fuel pressure just to end the annoying alarms when the INDICATED pressure drop to zero (Tenths not possible).

So the only suggestion I can add is perhaps not let the fuel pressure concern you compared to a possible fuel delivery issue as already discussed.
 
worn carb float?

Another item to check is to see if the carb float pivot has worn to the point where it would allow the float to touch the sides of the bowl. This can make the float hang and prevent the needle valve from working properly. Have someone knowledgeable drop the carb bowl and check for any shiny wear spots on the float.

I had a similar problem with fluctuating fuel pressure that could be "cured" with the boost pump. I replaced the fuel pump and installed a reman carb and fuel pressure has been solid since. I think the pump was the issue in my case but a sticking float can also cause problems.
 
Add me to this list

To All,

Thanx for the discussion about this matter. I am having the same
exact trouble. RV6 w/0360 ie: and using the Facet Pump the revive my engine with I exprerience this trouble - it's quite alarming.
(**** - I hate crashing !!!!)

I've check the ENTIRE fuel system 2 different times without a satisfying
result.

Okay - this time -- I'm buying ANOTHER Engine Driven Fuel Pump --
and -- sending in my carburetor for repair/verification of the Float,
Re-inspecting all fuel and vent lines, Gascolator, checking for leaks
and so on.

If anyone has any more ideas, please reply to the Website before
someone becomes a tragedy.
 
Had the engine ever stopped running during take-off PRIOR to installing the new Facet fuel pump? If the engine had never quit before...and after installing a new fuel system component the engine did quit...look to that installation for a problem.

A 0.5 psi fuel pressure may still have the engine running all day.
 
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fuel system

Get rid of the gascolator and replace it with all metal race car filter behind the firewall. Install a shroud with ram air on the engine driven pump. Try to avoid 90 degree fittings in fuel lines. All lines forward of firewall should be highest quality hoses with firesleeve. Try to avoid vertical curves in hoses. In other words the line from firewall to pump should not run uphill and then downhill or vice versa, all excess hose should be oriented horizontally.
 
Another thing to try

I recently started flying my RV-4, which has a tight cowl and a very tight engine compartment. I experienced "vapor lock" problems on my first few flights, but the problem was most evident on rollout after landing. I had to tow the aircraft back to the hangar after the first few flights, because the engine died shortly after landing and wouldnt restart until the engine cooled off.

For me, the fix was a piece of fire sleeve over a short section of stainless steel tubing I ran from the firewall to the gascolator. Lesson learned: insulate ALL of your FWF fuel lines from heat.

As a precaution, I now run the Facet pump all the time. If it ever wears out, I'll buy another one. I'm a glider pilot, so landing dead stick isn't at the top of my list of fears, but a Facet pump is cheaper than a broken wheel fairing from a well executed off-field landing, so it's cheap insurance in my book.
 
Thanks guy's
Lots of good info we hadn't thought of for us to look at.

Geico266
Sorry if I was misleading but it is occuring most often when cold not hot.
" Make sure the facet pump is in good working order." I have wondered about the facet pump if it could somehow cause a restrictsion when it is off? Any body ever found this to be a problem?

sig600:
no fuel leaks, at least we can't smell fuel anywhere and I've got a pretty good nose. Have checked vent lines for obstructon and found none.... routing looks good at first glance, may have to dig deeper on this one however.

rv8r999:
he is burning stricktly 100ll...he does not have a fuel flow meter.

walt:
thanks for the fuel line "flap" heads up...will start taking off fuel lines and checking.

smo:
cam issue is interesting but wouldn't a worn cam continually show a low pressure and not be intermittant?

rfazo:
doesn't matter how much fuel on board or which tank is selected, it does it with both tanks. interesting you see yours drop to as low as .5 with no issues or concern... we have always boosted back up with the electric if we see it this low in fear of it quitting. we have seen the pressure drop to .5 in straight and level flight also.

n816kc:
pulling air without leaking! I hadn't thought of that... is that really possible? May be something to look into....Just thinking out loud here but if the original builder had flared some of the tubing with the wrong angle or just had bad flares could they possibly pull in air without leaking?

sam:
thanks for the float issue, we may be looking into it but i'm not sure how this could show up as low pressure between the engine driven pump and the carburator.

drycreekrv:
Sorry you are having the same issues but on the other hand it is good to know we are not alone. Have you already replaced the engine driven fuel pump once and going for your 3rd one?

ron:
didn't replace the facet fuel pump we replaced the engine driven pump. Facet may be next however.

foka4:
I agree about running the facet fulltime, but if it quit and the engine driven pump wasn't producing....I don't want to be in that airplane. We have thought about putting a second electric pump in line so we now have three fuel pumps 2electric and the engine. Run one electric fulltime along with the engine pump and use the second one only if the first one finally reached its limit and quit during flight. I would rather find the problem and fix it instead of just putting a band-aid on the situation however.

thanks again, keep the ideas comming!

doug
 
Something to check

Doug,
I didn't read everything in every post but I'm leaning toward the "air leak" that some posters mention.

One place that this could happen is the gascolator O-ring. It could be damaged and rolling or something. It could let air in but keep fuel from leaking. I'd check it good and put some fuel lube on it.

Ok, I went back and read more of the posts and the gascolator seal has ben mentioned already.
Check it twice!

Good luck.
Mark
 
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As a precaution, I now run the Facet pump all the time. If it ever wears out, I'll buy another one. It's cheap insurance in my book.

Most all modern autos run electric fuel pumps 100,000 miles (about 2500 hours) with no problem. My next project will have two electric fuel pumps. A main that will run all the time, and a back-up. No mechanical pump.
 
I have wondered about the facet pump if it could somehow cause a restrictsion when it is off? Any body ever found this to be a problem?

I had a Facet pump that would make pressure when on but restrict flow when switched off. It was in a car, but that doesn't really matter. I would check the pump and make sure that it flows fuel when "off" and is correct for the application. Facet makes dozens of different models that look alike, some including check valves that could stick.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
Low fuel pressure

All those suggestions are great. I also had the problem of low mechanical fuel pump pressure. My engine never quit but I was sure concerned with the low .5 pressure. I lowered my fuel breather intakes just a tad more into the wind stream and the pressure came up to 1 just enough to make me feel better. I never had a problem though. I don't put screens in the vents for fear of ice build up when flying in clouds.
That's my 2 cents
Don
 
There is a screen on the suction side of the little Facet pump.

I had some trash there one time and severely restricted the fuel flow.
 
My money is on the mechanical pump pulling air into the system through the gascolator. There's not much else that could cause this.
Danny
 
Most all modern autos run electric fuel pumps 100,000 miles (about 2500 hours) with no problem. My next project will have two electric fuel pumps. A main that will run all the time, and a back-up. No mechanical pump.

I have 2 electric pumps and the mechanical pump. No shortage of fuel pressure here. :)
 
I have a carbureted RV9A and fuel pressure is between 3 and 5 PSI. Very often before take-off is 4.9 and when I switch the pump on it remains at 4.9. Never came down, neither in flight, under 2 PSI.

I will try to disconnect the fuel hose enetering into the caruretor and perform the fuel check with the electric pump on. This will at least exclude you have some restriction in the line.
 
Fuel pressure

I had a similar problem on my 0320. Replaced the boost pump, same problem; replaced the carburator, same problem. Finally replaced engine driven fuel pump (pain in the @&$&!). Problem solved! Just my experience. Yours may be different. Good luck, it's no fun when the RPM starts to follow the fuel pressure down.
 
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