High Fuel Alarm Question

Has anyone in the 12 world had to replace the electric fuel pump because of high fuel FLOW failure (not pressure) indications on the D180 causing the Rotax 912 to run rough? Lost power at 200 ft on takeoff with high fuel flow alarm and misfireing engine with both pumps running normally. Ferry home on mechanical pump after troubleshooting with nothing found and no alarms using only mecanical pump on my ELSA 12. Found black exhaust pipe carbon indicating running rich. Checked fuel system and drained it, found very very small amount of water in 10 % ethanol high test fuel upon examination of gascolator. Suspect excess flow of fuel to engine causing rough run and power loss. This definitely got my attention and needs to be fixed as I was lucky to have a 5000 ft runway to put it down on. Need Expert Help from the best VAF builders, Thanks in advance for any and all inputs. Doug R.

I don't own a Rotax, but others over the years have reported similar problems, all due to a float absorbing gasoline and sinking, opening the valve. You can do a search of the forum for this.

Unless there is something wrong with one or both of the carbs, the electric pump operating can't cause high fuel flow.
The only thing that would allow high flow is if the float valves in the carbs have been over come by excessive pressure (you said there was no high pressure alarm), or the are not functioning properly because of damage or contamination.

It likely worked ok with the electric pump off line because it lowered the fuel pressure enogh for the engine to run ok, but I bet it is still not running like it should.
I would pull the float bowls off and look for contamination, and clean all of teh carb passages with air.

The 912 carbs will not tolerate any contamination.... that is the cause of a large majority of the engine performance problems.

A little more info about the airplane would be helpful... how many flight hrs, etc.

Some RV-12s have experienced partial power loss on takeoff that turned out to be a bad engine driven fuel pump. The symptoms were low fuel pressure, high fuel flow, and rough running engine.
Perhaps N223JH will reply.
Joe Gores
http://www.vansairforce.com/community/showpost.php?p=540570&postcount=10

Need some guidance

I am suddenly experiencing the same issue on takeoff.
The engine starts and warms up fine and smooth.
Upon, adding power at takeoff the engine went rough and I could smell some fuel. We stopped and pulled the top cowling off and could see just a little fuel in the aluminum below the carb on the pilot side. We pulled the float, cleaned everything, didn't find any smoking gun there.
Today, it happened again.
This time when it was running rough, did an ignition check which did not change anything so we are thinking it is more fuel flow/pressure related. There was also a little fuel below the pilot carb.
I don't think this occurred until we installed the new fuel pump which causes the fuel pressure to increase. I have read where others have had the fuel pressure increase with the new/improved mechanical fuel pump.
Right now I am suspecting the fuel pressure but not sure why it would only affect the one carb. It seems like the normal pressure is just over 5psi.
I would like to reinstall the old fuel pump but we had to send it back.

Any advice on troubleshooting would be helpful.

My first home built had two electric fuel pumps in parallel. During takeoff I had both running. It flooded the carburetor resulting in stumbling performance for lack of a better term and soot in the exhaust. Once I relied on just gravity the carburetor ran fine. It may have nothing to do with your issue, but take it as a possible line for investigation if nothing else pans out.

High Fuel Flow warning Skyview

Yesterday I filled up the tank to its max capacity to check the new fuel overflow installation. After resetting the fuel computer to "full", I took off for an endurance check flight.

The plan was to fly in 15nm circles around the airport at 5000ft at 5000 rpm and 100kt, so I could start playing with my k-factor adjustment.

Based on previous flights, my consumption in the above settings has been showing around 7,5 gallons, though the real measured ones have been closer to 4 gal/h.

Once in cruise altitude and without any other noticeable event, parameter or behavior changes, the computer started showing >14 gallons/h and displayed a warning on excessive fuel flow.

With a full tank, and close to my home airport, I figure I could stay aloft a bit more to get data for troubleshooting (keeping an eye on the fuel totalizer and the Moller gauge, of course).

About 60 minutes with the high FF warning flashing, the consumption was still constant at the expected 4gal/h level. I went to idle in flight several times to check the flow behavior, and indeed went all the time down to 3 gal/h, at 2000rpm, but went up to 13-14gal/h, when returning to 5000rpm.

When I had already given up on the fuel computer, and feeling confident that there was a normal consumption rate based on the fuel gauge and the Moller, as suddenly as it came, the warning disappeared, and fuel flow returned to the usual 7,5 gal/h...

After 3 1/2h in the air, and 1h warning of 14gal/h flow, I still had over 6 gallons in the tank...

Today I've check the Skyview data on SavvyAnalysis, and it shows that, with all other parameters staying somehow constant, the fuel flow suddenly doubles and later on returns to its usual level.

My first guess goes for a defective red cube, but before getting a new unit and the hassle to mess up in there, I'd like to know if anyone has ideas on where else to check.

Thanks in advance!
Godo.

Did you try shutting off the electric fuel pump at any time during the high flow indication? If you search for old threads on this topic you will see where there have been erroneous high FF indications before at 5000 feet or above with both pumps running. Both D-180 and SV. A definititive cause for this was never identified to my knowledge, but the work-around is simple. Turn off the electric pump at altitude.

See the other active thread on this topic for procedure to get accurate fuel consumption numbers.

It would not hurt to check all of the connections and splices and connectors. Sometimes D-Sub pins appear OK but are not fully in position.
I'm not saying a bad connection is the problem, but it is worth checking before spending money.

Mich48041 said:

It would not hurt to check all of the connections and splices and connectors. Sometimes D-Sub pins appear OK but are not fully in position.
I'm not saying a bad connection is the problem, but it is worth checking before spending money.

Click to expand...

I could use this too, thanks Joe for spending the time to provide the wiring diagram.

Thanks for the hints. I'll try to avoid the red cibe replacement if I can...