Joshua's RV-9A Project

Precisely which piece is the “heart” of the FI system, I don’t know…but it seems like a worthy description of the fuel distribution spider, which has 6 different fuel lines, plus a control cable, connected to it.

A short flight test this morning — with the #2 and #4 nozzle lines reversed — indicated that the cold EGT followed the line/port, and did not stay with the cylinder.  #4 was now the one dropping to ~500 degrees, while the others stayed higher.  A couple phone calls later to Aero Sport Power and Airflow Performance resulted in AFP saying that it seems something isn’t right with the fuel spider.  The theory is that the #2 port is flowing richer than the other three (and this agrees with both flow tests I’ve done, though the difference isn’t much at all), and this extra fuel at idle is causing the cylinder to run cooler.

So as a first step, at their request, I’ve pulled the spider and purge valve assembly (it’s one interconnected piece) off the engine, boxed it up, and shipped it off to the Airflow shop.  Sadly, it won’t arrive there until Wednesday morning, even with 2-day shipping.  Depending on how long it takes to service and ship back, I’ll expect to see it back here shortly after Labor Day.  While it’s at the shop, they will test and rebuild as necessary to match the flow.

AFP also believes the stumble may be caused by vaporizing fuel…a theory I also entertained briefly (this by giving them only the symptoms, not suggesting any particular problem).  So, we’ll attempt to solve the equal flow issue first, see if it helps the stumble, and then proceed to working on the stumble if not.

Allison also brought Mom and Grandma out to the hangar for a brief visit this afternoon, and mom got to try the plane on for size.  Someday when she’s back in state, we’ll get her up once the flight test is over.