high fuel pressure question

[banker]

Been struggling with a problem related to High fuel pressure alarms going off intermittently on my plane. I have a Rotax 912 ULS on a high wing. Avionics are all Garmin and the PFD is a G3 Touch. So far we have changed the Transducer (which is a Electronics international FT-60) and the electric fuel pump. Alarms at 7.2 PSI. I have taken a log dump from the G3 and the pressure has peaked at 8.9 psi. Given this is a gravity fed system, and the alarms are going off in cruise, we are at a loss. The A/P believes its a Garmin related issue. Any thoughts/ideas?

[3Dreaming]

Where is the vent for the fuel pump drain located? It should be in a neutral pressure area, and many mechanics don't read SB and place it incorrectly.
The Electronics international FT-60 is a fuel flow transducer, not fuel pressure, so changing it will not effect you pressure readings. The airplane being a high wing really doesn't factor in with a electric and engine driven fuel pump, but the location of the pressure sending unit could be an issue.

[ShawnM]

Your first problem is that you have an A&P working on your LSA. Had you had a LSRM working on it he would have known the difference between a fuel flow transducer and a fuel pressure transducer.

Hold on while I climb down off my soapbox..........I would suggest checking the ground connection for your fuel pressure transducer. Bad grounds on electrical sending units can wreak havoc on engine sensors and cause erratic and intermittent readings like you are having. I'm assuming it's either a VDO or a Kavlico unit. Hopefully it's mounted on the firewall and not on the engine somewhere. This will extend the life of the transducer. How old is the fuel pressure sender?

[banker]

Thanks. No idea, but I’ll get some input from A/P. If your theory is correct, this suggests that the actual fuel pressure is potentially OK ( which could be the case as the plane flys very well) but is more a sensor/misreading issue, which is what the guy is telling me. Is my understanding correct?

[banker]

Your first problem is that you have an A&P working on your LSA. Had you had a LSRM working on it he would have known the difference between a fuel flow transducer and a fuel pressure transducer.

Hold on while I climb down off my soapbox..........I would suggest checking the ground connection for your fuel pressure transducer. Bad grounds on electrical sending units can wreak havoc on engine sensors and cause erratic and intermittent readings like you are having. I'm assuming it's either a VDO or a Kavlico unit. Hopefully it's mounted on the firewall and not on the engine somewhere. This will extend the life of the transducer. How old is the fuel pressure sender?

Yep my apologies , may have been using the wrong term. It’s actually the manufacturer that is attempting to resolve the problem . My plane is 2020, the problem is that the company are located in the other side of the county and we have been at this for a while. In any case given the arg of the plane, everything is relatively new. I’ll check the equipment list to find out the type of sender. I am hoping that the actual engine is functioning fine. It’s certainly flying great and that the problem is more related to the electronics-avionics as you suggest . Thank you for your input.

[JimParker256]

Like others here, I'm very confused by your question. You state that the fuel pressure is high, but then state that the A&P (or maybe the manufacturer) replaced the EI FT-60 fuel flow transducer to resolve the problem. That's crazy, as the two systems are completely unrelated.

Fuel flow (FT-60) is usually installed in the fuel supply line – typically between the gascolator/filter and the fuel pump. The fuel in a high-wing aircraft without a secondary fuel boost pump would be gravity fed all the way to that FT-60 fuel flow sensor. The transducer itself basically a little "hamster wheel" turbine that turns as the fuel flows through the line, generating current pulses that the gauge interprets as fuel flow.

Fuel pressure is measured at the output of the Rotax engine-driven fuel pump, with a pressure transducer. As the fuel pressure increases, the resistance (in ohms) is translated to fuel pressure at the gauge.

As someone else mentioned earlier, when you start getting erratic gauge readings on electric transducers, the issue often turns out to be a faulty, intermittent ground. (I had this issue with my oil pressure gauge. Removing, cleaning, and re-tightening the ground connection resolved the issue immediately.)

[banker]

Hi. Once again, I maybe using the wrong terms.

My plane is a new 2020 SlSA. From delivery I have been experiencing erratic fuel flow readings. Despite numerous attempts, including taking my plane back to their factory, the vendor/builder has been unable to resolve the issue, despite assurances its been fixed. I have been told (by their support people) that the fuel pump and transducer have been changed, and that is the case, based upon the updated equipment list. The symptoms were originally very infrequent "low" fuel pressure warnings. last week I took my plane out for a long flight (3 + hours) and had a series of intermittent but constant over the duration of the flight "High" fuel pressure warnings. its been quite challenging working with the builder (who are in a different part of the country) and with my limited (but growing) technical knowledge. Hence my reach out to this community. I have a Rotax 912 ULS and a full suite of Garmin products on the avionics side. The builder is now of the view that its somehow a Garmin problem. Based upon some of the comments, I am not so sure. I hope this clears up some of the confusion ??

[3Dreaming]

Your first problem is that you have an A&P working on your LSA. Had you had a LSRM working on it he would have known the difference between a fuel flow transducer and a fuel pressure transducer.

I typed a response last night from my tablet that must have not posted.

I take your slam on A&P's as a personal insult. I am an A&P since 1983, who has been working on SLSA aircraft since 2007. I feel as an A&P that I am fairly knowledgeable when it comes to light sport aircraft, and do a good job working on them. I think most of my customers feel the same way, at least I hope so. It doesn't really matter what letters you have behind your name, there are good an bad of all. The worst I've seen over the years did come from a A&P, and it was beyond negligent. But from what I've heard it was not because it was a SLSA, some people just don't do good work. That being said I have also seen some pretty poor work from LSRM too. The second worst SLSA that I've seen was worked on not by a A&P or a LSRM, but rather a Repair station specializing on ultralights. It involved kinked oil lines and the substitution of the incorrect sized fuel lines during a rubber replacement. They also left a forum member with a major fuel leak because of the same type of issues.

[designrs]

Can you get on a forum with other owners of your same make and model plane to see if this is a brand related issue? I say this because the aircraft manufacturer is responsible for designing, fabricating and more importantly routing the fuel system on your aircraft. Sometimes the way the fuel system is installed (check valves, hose fittings, returns, etc.) can cause abnormal fuel pressure variations. All “Rotax fuel systems” are not equal and they can sometimes be finicky.

Sometimes it’s not a simple as the pressure sender or electronics, although those items can be checked by swapping out components. Also have your A&P check the hose ties which secure the fuel lines. They should be snug but not so tight as to restrict fuel flow. Fuel flow restriction will sometimes raise fuel pressures.

Perhaps there are other owners of the same aircraft here. Exactly what plane is it?

[banker]

Exactly what plane is it?

its a Texas colt 100. To the best of my knowledge there are only 8 flying at the moment. Mine is the only one with a full Garmin suite.

[designrs]

Exactly what plane is it?

its a Texas colt 100. To the best of my knowledge there are only 8 flying at the moment. Mine is the only one with a full Garmin suite.

It may not be Garmin related. Are any of the other planes experiencing the same issue?

[banker]

No. I asked the builder that question. They actually took my plane back to the factory and left me with there demo plane. During the time I had it, I did not experience any problems at all with fuel pressure.

[designrs]

Good that you have manufacturer support. Let them fix it as it might require swapping out several parts to troubleshoot it.

I went through months trouble shooting a fuel pressure issue. (Different manufacturer.) First I swapped out the sender then the avionics. Then hooked up an analog fuel pressure gauge for on-ground testing. The plane was a few years old. Eventually I ended up upgrading the entire fuel system to newer manufacturer specifications. Then all was well.

Things learned:
1) How finicky fuel pressure can be
2) How all the installation, different components and hose routing can contribute to fuel pressure issues

Please keep us updated on your progress and solution.

[designrs]

Rotax fuel systems get complicated due to the return line, different hardware, different restricter jets for the return line, Y-connectors and backflow restrictor valves.

Once you rule out electronics, then there is all of this other stuff to look at.

[banker]

Good that you have manufacturer support. Let them fix it as it might require swapping out several parts to troubleshoot it.

I went through months trouble shooting a fuel pressure issue. (Different manufacturer.) First I swapped out the sender then the avionics. Then hooked up an analog fuel pressure gauge for on-ground testing. The plane was a few years old. Eventually I ended up upgrading the entire fuel system to newer manufacturer specifications. Then all was well.

Things learned:
1) How finicky fuel pressure can be
2) How all the installation, different components and hose routing can contribute to fuel pressure issues

Please keep us updated on your progress and solution.

Actually getting frustrated with the manufacturer, hence reaching out to this forum. I feel like I need to look elsewhere for a solution. The problem is it’s so new that there is not any experience with these planes in Florida. Moreover, I do not have a LSA mechanic on my field KSRQ.