RV12-iS. 85hrs on engine. 93E10 fuel.

 Very Very hot weather. Aircraft is heat soaked. As in, cant handle the seatbelts, hot. Engine start, runup and climb are no issues.

Set full power climb to 10.5k passing 9.8k ft, engine begins to degrade in power. I check fuel pressure and its flashing red on the Garmin at 38psi.

I jockey the throttle, basically no RPM changes between ECO and PWR mode. Around 5100rpm for both.  I realize that i should probably stop climbing...

Immediately lower nose and begin descending. Reduce power slightly. Fuel pressure hops back into normal range, around 41psi. I initiate descent to 9.5k feet and bring power to about 95% throttle per the fadec information page.

As I cruise at 9.5k, fuel pressure slowly increases from 41psi all the way back to 48psi(normal for my aircraft) over the course of 1 hr. No other issues the rest of flight.


Any ideas? This instance absolutely scared the daylights out of me!


  • Re: Possible Vapor lock?

    by » 6 months ago

    This exact scenario plagued my RV-12iS was well.  I also noticed this starting under 100 hrs, and continued for several months, through both mild and hot temperatures.  Living in Arizona, I would fly with ground temps over 100 degrees.

    Have you downloaded your diagnostic flight data from your EFIS?  Mine is Dynon, HFX-1100. I noticed some trends during the low fuel pressure events. 

  • Re: Possible Vapor lock?

    by » 6 months ago

    I’ve got a 12iS too - 200 hrs and also use 93E10.  I experienced a similar, not as bad, situation last Sunday.  My temperature was in the low 80s on take off, so not as hot as you were, but climbing through 7500’ I noticed the fuel pressure continuing to toggle between 41 psi red and 41 psi black.  I leveled off and the pressure fluctuations gradually slowed, held steady at 41 psi black, then slowly climbed back to my normal cruise pressure of 43-44 psi.  It’s not the first time I’ve experienced this, but I have written it off to vapor lock.  I’ve even insulated and fire sleeved the Rotax fuel line that crossed between the right and left fuel rails, hoping that might help - see attached photo.

    So, I’d be interested too in hearing what others might say on this issue, but wanted you to know you’re not alone. 

    Edit:  I see Edmond posted a similar issue while I was typing my response.  So that’s three of us.

    32988_2_AC3F21CE-05C4-45EF-9BB5-F11A47AA898B.jpeg (You do not have access to download this file.)

  • Re: Possible Vapor lock?

    by » 6 months ago

    I haven't downloaded the data yet. I figured id ask the hive mind first.

    My feeling is vapor lock, as I haven't had his issue until these recent "heat waves" swept through the southeast. I know that the hotter the mogas gets, the more and more it vaporizes.

    Did you mange to identify the problem with your bird?? 

  • Re: Possible Vapor lock?

    by » 6 months ago

    Why don't you run a tank of 100LL and see if it goes away?


  • Re: Possible Vapor lock?

    by » 5 months ago

    My normal fuel pressure during these events was low, like Bob's, generally at 43-44.  I made two changes.  First, I replaced the fuel pressure regulator assembly, about $340.  NOT the entire regulator, just the removal assembly.  Very easy job.  I did this reluctantly,  Not sure if it helped.

    I also switched to 100LL shortly after.  Problem disappeared shortly after and has never returned.  It was more worked carting gasoline to my hangar, not to mention rather dangerous.

    I think the 100LL solved the issue.  However, I notice now at engine start, fuel pressure is often low, as low as 38 PSI, which is in the red.  This is when I turn on ONLY PUMP #1.  I initially solved this by turning on PUMP #2 instead of #1.  Not sure why only pump #1 is fluky with 100LL.

    The real weird issue was during the diagnosing, and looking at the Dynon data, immediately prior to low fuel pressure events, and for the duration, my data logs showed NEGATIVE AMPS off the generator, and several rows of diagnostic data would not be recorded.  I stopped looking at my logs for some time, and overall, this issue no longer presents.


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