High Fuel pressure after filter change.

Interesting factoids related to this discussion…

A few years back Rotax recommended the fuel pressure sender for injected engines be placed between the pumps and fine filter just as Michael’s is. This was done so that a high fuel pressure reading would indicate a dirty (fine) filter.  Then more recently Rotax provided a hub for the fuel pressure sender right at the fuel rail just before the pressure regulator. This new position provides an accurate pressure reading at the fuel rail, which is arguably the most important thing, but in this case a low pressure may indicate a dirty filter.  They now consider a sender that is installed before the fine filter as “optional” whereas the sender at the fuel rails is mandatory.  But considering how much pressure these pumps will make, without the optional sender the filter could become quite dirty before you would see the pressure drop at the fuel rail.  

Another interesting point is that the fuel pumps on the injected engines, when both running, operate in series.  With the pumps in series the unrestricted flow rate with one or two pumps remains the same. However, the available head pressure is additive. You don’t see this pressure increase with an unrestricted flow, but the difference in pressure with both pumps vs one pump can be dramatic if the flow is restricted.  Thus, the reason that the one pump test as RW suggests is a good one.  

Good point Jeff. Never looked at it that way.