odd dips in fuel pressure, pump problem?

Interesting comment about the pump drain line.  I hadn't seen that note, but I don't believe it's location puts it in ram air or slipstream.  It's literally not been moved in over a year and a half, and I don't think the extra airflow would affect it.  It also wouldn't explain why it takes 40 min to occur.  I will take another look at that line the next time I'm there.

Thanks,

Rusty

Looks like it's  time for another research project. Time to test fuel temp in the fuel lines at idle after warm up, cruise and after landing. 

I still don't  think it's  "always" fuel vaporization without ruling out other causes. An open mind and good diagnostics is always a good approach. The fuel is in a hose, it's  supposed to be in fire sleeve, there is cooler fuel moving through the hose and there is supposed to be a recirculation line.  If it was always fuel vaporization with 91 Oct. then thousands would be grounded or having issues especially in hot climates, but they aren't  all having issues. During some research I never had under cowl yemps over 145F ever. Then the fuel is insulated in the rubber hose, fire sleeve and being replaced with cooler fuel while running. Vaporization does seem to be more frequent after landing when under cowl temps rise, no cooling air, no cooler fuel replacement and no recirculation. So now this all gets heat soaked. I've  seen my fuel pressure lower on startup after the engine sits for 45 min., but comes right back to normal after cooler fuel is introduced. If auto fuel is so bad then how could a Mfg recommend it for use.

I think it's  time to install a fuel temp gauge in the fuel hose system to do a real time temp test which I don't think anyone has done. Without testing blaming fuel vaporization from a temp under the cowl ALL THE TIME may be premature.

Even though Rotax doesn't  like the exhaust pipes wrapped if done CORRECTLY it doesn't  cause an issue and definitely  drops under cowl temps when I did research on it on a couple of engines. Some of the wrap Mfg's  say it reduces radiated and convected heat by 70% I don't  always believe some Mfg claims, but if it did just 50% that's a huge heat reduction on wiring, hose and other parts. There are tons of Rotax wrapped exhaust out there  around the world with no issues. I bet I've  wrapped 80+  engine pipes in 15+ years and never had an issue. Stemmie and some other Mfg's  do it right from the factory. What causes damage to pipes is over wrapping and causing too much heat to the exhaust pipe. 

Remember you can damage anything when done wrong even using just a plain screwdriver. You can damage a Rotax engine if you do an oil change wrong. Education is everything.

I have had a latest type pump with approx 90hrs on it, but it went suddenly from normal to zero,  only noticed by looking at fuel gauge ( no splutters etc) flew back to base with electric pump. Replaced pump with new one and all good, pulled faulty pump apart and one of to valves in the pump was loose in its seat ( can't remember whether inlet or outlet valve ) spoke with dealer and governing bodies with no reply, with the local L2 saying it was the 3rd time he had seen this. I say change the pump and see if it changes they aren't difficult to change out