Sport Pilot Talk

This is from another forum, don't know whether it applies or not?

http://www.dynonavionics.com/docs/suppo ... 20414.html

Nomore767 wrote:This is from another forum, don't know whether it applies or not?

http://www.dynonavionics.com/docs/suppo ... 20414.html

Thanks but not applicable. My fuel pressure sender is VDO... and just replaced. Same issue before and after replacement.

SportPilot wrote:I think fuel flow is probably more important than fuel pressure. As long as the engine is getting the fuel and air you are commanding with the throttle, there may not really be an issue.

I'll watch the flow too.

Andy: I do think I can replicate the problem over a costal airport.
Might be worth a try.

It usually does it when I hit the beach... which leads me to suspect some sort of atmospheric issue... but:
1) the sender was replaced
2) pressure fluctuates with throttle... if it were electrical that probably wouldn't happen unless it was associated with RPM.

What does Sport Cruiser say about the issue?

designrs wrote: 2) pressure fluctuates with throttle... if it were electrical that probably wouldn't happen unless it was associated with RPM.

I have seen and heard about some strange things on some of the Rotax powered LSA. I had a airplane with a loud engine whine in the headset that varied with RPM. I found the problem by isolating electrical equipment. The GPS wound up being the source of the problem, because it was feeding power back through the ground. Strange things can happen, and it won't cost much to check it out.

Nomore767 wrote:What does Sport Cruiser say about the issue?

Thus far the obvious:
1) Make sure fuel pump drain hose is trimmed 12" back INSIDE the cowling. (Done)
2) Reposotion fuel line to mechanical pump. (Done)
3) Have you done 5-Year rubber? (Not due yet. Considering.)

US SportAir is preparing for a homecoming / open house this weekend, so I haven't received an immediate reply to further questions.

I think at this point I either:
a) Put a temporary analog fuel pressure check gauge in. (Per Paul)
or
b) Test the condition hard in flight. (Andy)
or
c) Replace fuel line rubber to elimate variables.

I need to determine if this is electronic or physical.

Put an inline mechanical gauge in and go fly. Then you can compare. The mechanical gauge doesn't have to be expensive for a 1-2 time comparison test. Should be about $20-$30 in parts. Depending on your fuel hose routing it could be heat related.

Bingo on heat related. Most of the time I get low fuel pressure is after a descent or flying into a warmer region (into warmer air)... AND I did have low pressure on a longer taxi in 85 degrees if I didn't turn on the boost pump.

I'm going to wrap the exhaust first. If that doesn't work then do the mechanical fuel pressure guage test.

designrs wrote:Bingo on heat related. Most of the time I get low fuel pressure is after a descent or flying into a warmer region (into warmer air)... AND I did have low pressure on a longer taxi in 85 degrees if I didn't turn on the boost pump.

I'm going to wrap the exhaust first. If that doesn't work then do the mechanical fuel pressure guage test.

Are you using mogas? Ethanol? I know people who have had fuel problems with mogas causing vapor problems in their lines in hot conditions.

I usually run 5% ethanol... BUT I've had the fuel pressure issue multiple times when on extended cross-countries running 100% 100LL.

Hi Rich,

If you need to re-route a fuel line to remove it away from any heat source and make sure it is in fire sleeve.

My 2c worth:

I have a 2006 StingSport low wing, 912ULS, fuel tank under the front cockpit floor. Grand Rapids Tech. Engine Information System which monitors and displays fuel pressure along with most other engine parameters. Fuel pressure is the only one that has ever shown anomalous behavior. I have changed out the fuel pump and the fuel pressure sensor, made no difference. I have had the low fuel pressure warning light come on (threshold set to 2.2 PSI) in all flight regimes... climbing out on a cool morning, in cruise an hour into the flight.... not at all, in a 2+ hour flight. I can't connect this with any engine operating or temperature conditions, it seems to be completely random. Every time the warning light comes on, I turn on the AUX pump and the fuel pressure goes right back up into the green (3+ PSI). If the sensor or gauge were faulty, would this happen? I don't think so.

Recently I wondered what would happen if I just ignored the warning light. Went up to 5,000AGL over the airport and loitered (cruise power setting), hoping the light would come on, and it did! I just left everything alone and after a few seconds, the light went out and the fuel pressure went back to the normal range all by itself. No engine hiccups at all.

Last week I took off for a 2 hour cross-country flight. A few minutes after takeoff (gliding distance to the airport) climbing out WOT, the light comes on. Again I just left everything alone and again, after a few seconds the light went out and the fuel pressure went back to the normal range and stayed there the rest of the flight. No warning lights at all on the 2 hour return flight.

From everything I read on this forum and from my experience, I conclude that (a) this is a randomly occurring condition that is widespread and seems endemic to the Rotax 912ULS (or maybe to Bing carbs!) and (b) it is a non-problem, even if the AUX pump should fail (of course I only have two data points to support this idea). Just my thought, don't take it to the bank.

I don't know how the float valves in Bing carbs work, but perhaps there is an on/off operation there... ie, maybe the float valves only open wide when the fuel level in the float bowls gets low, rather than maintaining a more or less constant level in the float bowls by trickling in fuel the way automobile carbs do. I suppose if both float valves opened wide at the same time, fuel pressure supplied by the engine driven pump could drop for a few seconds while the float bowls refilled. This is a wild and crazy idea but all I can come up with. Yeah, I know mixture in this sort of carb is a function of the fuel level in the float bowl. I'd like to hear others' thoughts on this.

This isn't the carbs. There are couple of items that could cause it, but it seems you may have already addressed these. This isn't something that happens to all Rotax 912's. So far I have only seen it on a regular basis with the RV12's and you are the first person so far I have heard of with a Sting. Maybe you have heard of others? I have a couple of Sting's that come to the shop and they don't have this issue. I'm beginning to think it is electrical in nature. I haven't heard of anyone that has had an engine hiccup with this issue and I'm wondering if it is real or not.

I would like to get one of these planes and put a mechanical pressure gauge inline and go fly and see if the pressure really corresponds to the low pressure alarm.

Thank you bstrachan, Roger and all.

Today I flew the SportCruiser in sub 80 degree temperature and cool overcast... a seasonal first in Florida. I'm thinking, "ikely vapor restriction due to temperature... today I will probably not have fuel pressure alarms". Sure enough, great flight... sightseeing down to 500 feet (multiple passes and maneuvers), flying the coast, two simulated engine-out practices down to 500', and multiple climb-outs... no issues.

THEN on short final into my destination airport Fuel Pressure Low alert!

I'm going to:
1) wrap the exhaust... as I want to do this anyway.
It will probably help during long hold-short on warm days.
2) if problem persists I'll hook up an analog gauge to test.

... if the problem persists, I'll be so %*@#^~ *#%**! that I may fly it straight to Arizona and give Roger his wish to trouble shoot this issue!