Bill,

 

Uh, vapor lock is no mystery regardless of the injected engine type.  Heat and low fuel pressure lead to vaporization.  Using my installation of an IO 320 as an example, one might consider the fuel path backwards from injector to the fuel tank.

 

1. Assuming there is no debris in the fuel that would block an injector, note that the spider and distribution lines are suspended in the engine cooling air intake plenum - assuming there is cooling air moving thru this area, vaporization is less likely here.  That is another story after shutdown.

 

2.  Line from throttle body to the spider.  Mine passes under an exhaust pipe and thru a fuel flow sensor located between the firewall and the rear of the engine.  This line (as all fuel lines fwd of the firewall) is fire shielded and that can help keep fuel from heating up at a hot spot.  Additionally, a small stainless steel shield is SS hose clamped to the exhaust pipe to protect the fuel line from radiant heat.  The FF sensor is in a warm dead airspace but does not get hot enough for vaporization. Fuel pressure is that maintained by the throttle body demands and the FF sensor location is often used by fuel pressure sensors and translated at the gauge into FF (like in my old Skymaster).

 

3. Throttle body is cooled by induction air unless turbo charged - if so, and if the turbo compressed air temp is too high, a vaporization problem could occur there.

 

4. Engine driven fuel pump to throttle body.  This line should not run too close to any high heat area.  In my case the fuel leaving this pump goes thru a tee with one side feeding a fuel pressure sensor.  For my engine the pressure in this line must be maintained above 12 psi and below 40 psi.  Delivered pressure is usually about 26 psi (even with the boost pump on).

 

5. Engine driven pump.  Ah, here is a devil as it can become heat soaked, vaporizing the fuel and then causing pump cavitation (if diaphragm pumps can cavitate).  Since this pump is usually drawing fuel at very little pressure or even a vacuum, this problem is likely for hot starts or high engine compartment temperatures in adverse conditions (idling at the hold short line on a very hot day).  This problem can usually be resolved by raising the pressure of the incoming fuel and/or causing fuel to flow thru a system that has a return line by turning on a boost pump (fuel thru a return line can cool the pump body).  My installation does not have a return line, Continental setups usually do.  Fuel from a wing is drawn up by the pump (vacuum) or, in my case, the header tank provides a "head" pressure to the fuel flowing to the engine pump.

 

6. Boost pump and line from it to the engine pump.  Ah, some differences can appear here.  In my case, the boost pump is in the engine compartment, mounted low on the firewall.  The line is away from any hot spot although it is in the engine cooling air exit and may present warm fuel to the engine pump.  Again, because of head pressure, if there is vaporization in this pump, it clears itself quickly and provides enough pressure to usually stop and reverse any vaporization further down the line.  This pump is used on hot day take offs and landings.  The measured pressured stays at about 26 psi.

 

7. Gascolator and line to boost pump.  While located in a warm area (gascolator is firewall mounted next to boost pump), there does not seem to be a problem here although some people have pointed a blast tube at the gascolator.  Mine is an old fashioned Cessna type with a remote drain control on it.

 

8. Selector to "gascolator".  I don't have a selector valve since all fuel comes from the main tank (header) that is automatically kept filled from the aux wing tanks.  While there is little possibility of vaporization here, a seal failure in a selector valve could introduce air into the fuel stream.

 

These areas are worth thoughtful review as sources of failure to deliver fuel to the engine.

 

Grayhawk

 

We sent off the fuel pump for inspection and overhaul. Due back late next week. Still no causal chain isolated....  Lancair inspected the photos and they believe we have 1/2" lines. Anybody know the best way to access to inspect these lines for both diameter and number of 90 degree turns?  As I reviewed the data, it is difficult to determine whether MAP or FF fails first. It occurs to me that some intermittent failure of the turbocharger MAP feedback control might also cause this pattern, though far less likely than FF. On the ground failures, the turbos were spooling up from idle. At FL 220 they were at full power < critical altitude.    (anybody know their IV-P crit alt from flt test?)  Since vapor lock remains mysterious and we have all this on-board data monitoring capability, I wonder if there's a way to monitor for bubbles in the feedline to the low boost and to the engine driven pump. In monitoring pilots for the bends (space suit prebreathing was used this week on the Hubble Mission), at Brooks AFB, we could early detect micro-bubbles in the blood with ultrasound before the symptoms were experienced by the "astronaut". As the bubbles get bigger you start to see problems as big bubbles lodge in important places like joints, heart, brain etc. Some kind of acoustic or optical detector might give us early warning.  Has anyone seen a takeoff mishap attributed to vapor lock? Particularly in the IV or TSIO-550B? Thanks Bill Miller