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  #11  
Old 06-29-2017, 06:41 AM
PilotBrent PilotBrent is offline
 
Join Date: Dec 2011
Location: Hackettstown, NJ
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Quote:
Originally Posted by omerward View Post
To answer questions: electric pump was on. After airborne I pulled the fuse and pressure dropped about 1 psi so I am pretty sure the electric pump is working the whole time. I'm using 93 octane mogas as recommended. A friend I contacted said he has same problem and he only uses 100LL. I have had the hoses off the pump and they are not kinked. Also, not a hot engine. First flight of the day. I was told this only happens with RV-12 and it is common. Hoping somebody has a solution I haven't tried. Doesn't happen on every takeoff or every flight even. Most solutions like blocked vent or kinked hose would be all the time and this is not. Sounds like a bad pump for sure but the pump is brand new and problem still the same. Two bad pumps maybe? Unlikely! Does anybody else have his problem?
Maybe there is a another failure causing some of these reports, but if you search on this site you'll come across instances where adding some or fully switching to 100LL resolves the intermittent low pressure readings in RV-12s. The -12 doesn't have an airbox by design as it gets very warm under the cowel. (I suspect that may be factor that is different that may other LSA 912 designs) I've had these occurrences from time to time for 3 years now. I'm personally convinced (most) of these reports are the result of using 93 octane mogas formulations (winter blends) in warm weather situations. Often in spring and fall when automotive supplies have been switched over.

Myself, rarely see this with the first takeoff of the day (cool air, cool fuel). As the day warms up, more likely to see them. Much more common when decending from altitude. Pressures drop into the yellow zone for me, virtually never in the red. Leveling off decent and within a few (long) minutes the pressures recover. I don't use 100LL very often at all, mostly just on long trips away from home. Have never seen this occur with 100LL in the tank. Anecdotally, some RV-12 operators routinely add a few gallons of 100LL to mogas and swear by it.

Yes, I chased the engine pump as culpret, even replaced the pressure sensor, flushed lines... Often its the more simple cause that's the one to address. Suggest switching to 100LL and try to replicate the readings yourself in a controlled way before driving yourself crazy trying to resolve. Just my 2 cents.
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  #12  
Old 06-29-2017, 10:25 PM
omerward omerward is offline
 
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Quote:
Originally Posted by D&M Dan View Post
I am also trouble shooting this low fuel pressure issue. I have just received a new fuel pressure sensor ($85.00), but have not installed it yet. Let me explain what is happening in my case and by the way I am using 93 octane w/o ethanol. Flights have been in varying temp ranges (40s - 70s). I also have the new vent system without a fuel cap vent.

I have done the following in between flights but have not solved the problem.
Flushed all fuel from tank with the electric fuel pump. No issue with the electric pump as it pushed 12 gallons fuel steadily and in a timely fashion. Added fresh 93 octane w/o ethanol Removed the strainer screen and found 0 debris. Flushed the fuel sensor hose as per maintenance manuel instructions. ( I did notice there appears to be not much pressure at the end of this hose, but I would expect that if it is reading between 2.0 and 7.0 psi) Checked the fuel pressure sensor wires. Installed a fuel pressure gauge and checked against the Dynon display. I am seeing about a 1.2 psi difference between gauges with the Dynon being lower on the ground (Hoping this is the sensor). Still pressure is only in the 4.5psi psi range with both pumps running. There is a slight drop of about 1.0psi with electric pump turned off. Downloaded the data from the last flight. The fuel pressure drop was gradual and over a 30 minute period. The Dynon download shows approx. 3.5 in the beginning of the flight gradually dropping into the 2.0 range where the FUEL PRESSURE warnings begin.

I plan to install the new sensor next, but not sure if this is the answer. Wondering if there is a way to check the mechanical pump, other than replacement.
Dan, thanks for sharing your efforts with me. Looks like we are tracking the same gremlin. Please let me know if you find anything conclusive. I will post if I find anything at my end.

Brent, thank you for responding with your 2 cents. Worth a lot more than that IMHO. I'm having trouble pinning it on the fuel though. Seems like the problem would be more persistent and less intermittent. The solution is there somewhere. Meanwhile my friend who runs 100LL says it is harmless and he just ignores it. That's one way to look at it. I will keep trying different things and will post if I find anything new.

Best of luck to you both and thanks for your responses.
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  #13  
Old 07-01-2017, 10:54 AM
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Piper J3 Piper J3 is offline
 
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Just a thought... sometimes electrical components are temperature sensitive. Could be that a batch of fuel pressure sensors may have left the factory that drift with elevated temp. We're only looking at a couple of psi difference and maybe sensor made out of spec would cause that.
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  #14  
Old 07-07-2017, 08:51 PM
omerward omerward is offline
 
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Well, I have been trying different things and thought I would share this with everybody. I've been fond of making short field takeoffs in the -12 because it does a great job and it's fun. This often involves a fairly brisk throttle advancement and a sharp nose up rotation. That's when I'm getting the fuel low pressure warning. My guess is that the brisk throttle creates a suction on the feed line all the way back to the tank. This combined with a sharp rotation just momentarily creates a situation of low pressure from the tank forward. Just a theory, but when I take the full 5 seconds to advance, as recommended in the POH, and don't rotate so sharply, I don't get the warning. I've tried it several times and it sure seems to work. Comments?
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  #15  
Old 07-08-2017, 01:17 AM
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Gagarin737 Gagarin737 is offline
 
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My plane is 4 years in the air and I had erratic fuel pressure indications from the beginning; fuel pressure at start up 2.5psi and completely zero at lift-off. During the flight it recovers a bit. Engine always run fine. Since the last annual I removed the silicone gasket (Dynon Tecnical Advisory) from the sensor and the indication is rock solid now 5.7psi.
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  #16  
Old 07-08-2017, 04:04 AM
BigJohn BigJohn is offline
 
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Location: Gloversville, NY
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Quote:
Originally Posted by omerward View Post
Well, I have been trying different things and thought I would share this with everybody. I've been fond of making short field takeoffs in the -12 because it does a great job and it's fun. This often involves a fairly brisk throttle advancement and a sharp nose up rotation. That's when I'm getting the fuel low pressure warning. My guess is that the brisk throttle creates a suction on the feed line all the way back to the tank. This combined with a sharp rotation just momentarily creates a situation of low pressure from the tank forward. Just a theory, but when I take the full 5 seconds to advance, as recommended in the POH, and don't rotate so sharply, I don't get the warning. I've tried it several times and it sure seems to work. Comments?
What do you see as the advantage of a "brisk" throttle advance in a short field T/O situation?
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  #17  
Old 07-08-2017, 06:01 AM
D&M Dan D&M Dan is offline
 
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Location: Webster, NY
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Recently I wanted to eliminate the new fuel vent system as the culprit, so I ran the engine on the ground at different RPM settings without the fuel cap on. I saw no difference with or without the cap, which by the way I have not drilled. I think I can state the issue is not the fuel venting system, unless you have some sort of blockage.
I also added 100LL fuel in an experiment to see if that would make any difference as suggested earlier. I flew the aircraft up to and including 10,000' over about an hour period. During the flight I had intermittent fuel pressure warnings at all phases of flight, so I do not believe altitude or any particular phase of flight can be identified as the problem specifically. I will download the data from the flight and see if I can find anything.
Finally I called Lockwood Aviation to see if it would be worth purchasing a new mechanical fuel pump to eliminate that as a problem. After talking with one of the technical support guys, I was told they receive many calls each week concerning fuel pressure issue in the 12. The person I spoke with believes the problem is related to the fuel tank placement and delivery system. They do not have a cure for the issue at this time, (nor do they believe it is up to them to solve this) and purchasing a new pump will not solve the pressure problem.
He told me for now to change the fuel pressure warning settings in the Dynon, and gave me specific settings to try,which I will attempt to do today.
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  #18  
Old 07-08-2017, 07:25 AM
Mitch757 Mitch757 is offline
 
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Location: Falmouth, MA
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About a year ago I replaced my Rotax fuel pump due to intermittent low pressure during takeoff and/or climb (1.5 psi). This was on the recommendation of the Lockwood technician after I also mentioned that there was a small oil leak from the tube coming out of the pump.

So far, this has solved MY problem of low pressure indications. My engine until recently had been running on alcohol laced auto fuel. (I'm now using unleaded Swift avgas).

I suspect, without any evidence, that the alcohol might have had some kind of effect on the old pump. I didn't take it apart since it was under warranty.

Mitch Garner
RV12 120260
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  #19  
Old 07-09-2017, 09:47 PM
omerward omerward is offline
 
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Quote:
Originally Posted by Gagarin737 View Post
Since the last annual I removed the silicone gasket (Dynon Tecnical Advisory) from the sensor and the indication is rock solid now 5.7psi.
Thank you for this info! I had not heard of this. Can't wait to try it. Sounds very promising.
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  #20  
Old 08-14-2017, 04:33 PM
D&M Dan D&M Dan is offline
 
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Location: Webster, NY
Posts: 82
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Well I finally solved my fuel pressure issue and I have to say I feel pretty dumb. After replacing the mechanical pump and the pressure sensor, nothing had changed. I only had 3.3 psi max dropping into the 1.9 psi range at times. Showing my disappointment a friend said lets check the build instructions and see if something got missed. We pulled the fuel return and pressure lines to make sure they were constructed in the correct orientation. They were..
As a last effort I decided to pull the upper banjo bolt and sure as shooting the valve had not been removed as instructed. I am not sure if I left that chore to one of my helpers or we just forgot it, but ultimately it is my fault. Solid 5.0 - 5.3 psi now.
I am relieved the problem is solved but I feel like a real dummy. However on to some fun flying now!
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