Fuel Pressure alarm

by Jim McConnell in General Tech Discussion 10 years ago

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Re: Fuel Pressure alarm

by Roger Lee » 9 years ago

Roger Lee

126 5.14k 4.58k

Hi Mike,

I find that senders mounted above the balance tube seem to last longer and don't get clogged with old stale fuel. It drains down away from the sender when you put the plane away. Then on a new start up it gets fresh fuel and never gets stale. I have not had to replace or fix a single sender in 6 years where it was mounted above the balance tube.

The senders I have seen that are mounted with a remote mount using a hose and that gets put on the firewall down below the balance tube seem to eventually (1 year) show signs of decreasing pressure and it can become intermittent. I have seen this multiple times and can usually clean out the sender orifice. The fuel trapped in the low hanging fuel line never gets replaced and just gets cooked and stale in the hose and it starts to clog the small orifice on the sender. Many think the sender is just going bad and then they replace the sender and when they remove it all the old stale fuel gets drained and the cycle starts over.
Seems the owners that leave the sender mounted directly to the balance tube fuel assembly block have too many vibration issues that kill the sender.

The auto fuel just sits in a low hanging hose on a remote mount and eventually like auto fuel does goes bad. Cooking it inside the cowl with engine heat certainly doesn't help.

p.s.
Talking about VDO senders.

Has this been your experience?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Fuel Pressure alarm

by James Ott » 9 years ago

James Ott

22 322 358

My fuel pressure sensor is remote mounted high on the firewall, which makes the connecting hose to the tee on the balance tube about level at rest on the ground and puts the sensor a little above the tee in flight attitude.

As stated previously in my description of low fuel pressure symptoms, this issue started immediately on the maiden flight and has been happening ever since (now at 160 hours-14 months). However I will check for blockage even though I know it is not the cause of the problem. I have had the sensor hose and orifices off several times for inspection.

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Re: Fuel Pressure alarm

by Roger Lee » 9 years ago

Roger Lee

126 5.14k 4.58k

I use a can of carb spray cleaner with the red 5" tube for a nozzle. I put this up against the hole in the sender and give a short quick squirt. This cleans the orifice area and exercises the spring operated mechanism inside. This seems to fix many with intermentent readings from being partially clogged, but certainly doesn't fix them all. Some are just bad.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Fuel Pressure alarm

by Mike Goodrich » 9 years ago

Mike Goodrich

8 123 0

James
Sorry I should have read your earlier posts where you said you'd removed the sender.

Having said that I think the need for the fuel pressure sensor to be ABOVE the "T" so that the pipoe to the sender is always going upwards needs a heads up for the forum or even in the Rotax installation manual, it could save a lot of owners headaches later on.

I see that you have a fuel pressure regulator that seems to be connected to the carb balance tube. I haven't seen this before (my previous experience was with a 914 and I've only recently bought an autogyro with a 912S) and it wasn't on my 912S when I changed over to fuel injection. Could somebody please point me towards the instructions for this it might help me understand the problem?

James you say that your problem is like Jim's and his occurs on the first climb out of the day as he passes 1000 to 1300'. Is your problem exactly the same or just similar? The question I'm asking is: is it altitude related or just that on a normal climb out at WOT you and Jim arrive at 1000' at about the same time after going to WOT?
I agree with you that, despite Roger's valiant attempts to defend Rotax's reputation, the statistics seem to indicate that the problem is probably in the new pump design.
My wild ass guess would be that this could be a time/temperature issue and that during the WOT climb out the pump starts to cavitate because the fuel in the suction line to the pump is travelling much faster (higher flow) and/or is getting hotter. In the pump industry we call this NPSHA (net positive suction head available). I must confess I cannot imagine a scenario that meets all the symptoms especially that this only occurs on the first flight of the day.
Why was it necessary to change the pump design/model? What is the difference between the old and new pumps, discharge pressure, flow or what???
Mike G

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Re: Fuel Pressure alarm

by Roger Lee » 9 years ago

Roger Lee

126 5.14k 4.58k

Of all times for this to happen. Today I went for a long flight in a Flight Design CTSW with an engine with 230 hrs. on it. My normal fuel pressure is 3.6 psi and has been all this time. Today I took off and it dropped to 2.1 and debated a turn back, but rode it out in the climb. After 2 minutes the pressure started back up and went to 3.5 psi for the next 3 hours and I had one other take off, but with normal pressure. The outside temp was about 40F and temps up at 8500' was 36F.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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