Low Fuel Pressure Alert

[gezer]

Where on this diagram would the fuel pressure sender be connected?  Problem I am having, when Dynon fuel flow is .1 then fuel pressure is 6.0 plus or minus a little, when Dynon fuel flow indication is around 4.0  then fuel pressure is 3.0 plus or minus about 1.     

 

[Tom Baker]

At the point where it splits to the 2 carbs.

[Isham]

On 6/28/2019 at 10:13 PM, Andrew Lane said:

Hi guys,

twice I’ve had this happen, fuel pressure drops and sky view starts freaking me and my CFI out with alarms about fuel psi, it goes as low as 1.4psi and doesn’t recover to normal (over 2psi) for about 2 mins.

Approx 10 gallons of fuel, coming in for a landing. Using some forward slip.

first time was a somewhat hard touch and go

Second time was today (days later, many normal flights in between), come in for a landing, crosswind gusts so we go around. Full engine throttle and steep climb angle (~68kt) then fuel pump starts alarming again.

anyone else have this happen? Very stressful....

as soon as engine throttle is reduced or level off things are normal again.

does NOT happen every flight.

Thoughts?

 

Andrew, did you ever figure out the issue?  My CTsw is doing the exact same thing during a couple of touch and go's today.

[procharger]

My SW has done this off and on over the years remove sender and clean with some carb spray

 and check wires clean them or just  move them around  and snug them up replace sender

it doesn't cost very much.

[FlyingMonkey]

The OP stated the airplane had ~10g fuel and was in a slip...first suspect is fuel starvation from unporting a pickup in the slip.  I'm not saying this *is* the issue, but if you see it primarily in lower-fuel situations, I'd want to rule out uncoordinated flight conditions before moving on to mechanical/electrical/fuel flow problems.

Also, does anybody have a handle on what the minimum fuel pressure is for a Rotax engine to run properly?  If the number is 1psi then an indication of 1.4psi is not really a problem versus 2psi. 

 

 

[AGLyme]

I have had the opposite issue... i.e. too much fuel pressure when both pumps are on (primary + backup).  Never red line, but the needle would go into the low yellow range of the gauge.

The acceptable fuel pressure range in the Ops manual for my 912is is 46.5 - 40.5 psi.  I recall Roger Lee telling me a year ago that he sees 43-46 psi for "everyday ops" and I believe that is the carb 912.  Where is Roger Lee anyway?  I miss his wisdom.

[Tom Baker]

43-46 is way to high for the 912 ULS. Without looking it up I think we set the high limit with the new style pumps to 7 or 7.2 PSI. The low end was around 2. Fuel pressure is not as critical as fuel flow. If you can flow enough fuel at 2 PSI or less the engine will run fine. You have a valve in each carburetor the allows fuel into the float bowl. When those valves are closed the pressure will be higher, and when they open the pressure drops. If both open at the same time as when high fuel flow is needed you may see a bigger drop in pressure. The flow needs to be sufficient to fill the float bowls back up and close the valves. According to Rotax a low fuel pressure alarm is acceptable with the new style fuel pump as long as it last for less than 5 seconds.

[Warmi]

2 hours ago, Tom Baker said:

43-46 is way to high for the 912 ULS. Without looking it up I think we set the high limit with the new style pumps to 7 or 7.2 PSI. The low end was around 2. Fuel pressure is not as critical as fuel flow. If you can flow enough fuel at 2 PSI or less the engine will run fine. You have a valve in each carburetor the allows fuel into the float bowl. When those valves are closed the pressure will be higher, and when they open the pressure drops. If both open at the same time as when high fuel flow is needed you may see a bigger drop in pressure. The flow needs to be sufficient to fill the float bowls back up and close the valves. According to Rotax a low fuel pressure alarm is acceptable with the new style fuel pump as long as it last for less than 5 seconds.

He probably meant in  kilopascals which would convert from 7 PSI to about 48 kilopascals.

[Tom Baker]

18 minutes ago, Warmi said:

He probably meant in  kilopascals which would convert from 7 PSI to about 48 kilopascals.

I suspect it was PSI. I think the numbers Roger gave were for the fuel injected engines, not ones with carburetors.

[Andrew Lane]

for the record, my problem was solved by replacing the fuel pump. which i later learned should have been done previously to comply with a service bulletin. no issues since. I did however have adjust the warning thresholds in dynon skyview as the new pump runs at slightly higher psi's. for my carb 912 i now routinely see....between 4.5 - 6.5 psi (off the top of my head).

[AGLyme]

With that much of a variance Tom, he must have meant the injected model, which falls in line with what my manual (injected) states... not the carb version.  My Roger notes must have been wrong, thanks for the correction.

[Isham]

Mine was down to just over 2 psi (normally around 5-6) for a few seconds during takeoff climbs.  I noticed if I pulled the throttle back 1/2" the low pressure warning turned off. 

My airplane has had the newer fuel pump installed.  If it is okay per Rotax maybe it's only a pucker factor. 

If "According to Rotax a low fuel pressure alarm is acceptable with the new style fuel pump as long as it last for less than 5 seconds" I would appreciate a link so I can read it.