Hi Bruce,

 

I have a true fuel flow sensor (not a fuel pressure-type sensor) between the engine driven fuel pump and the throttle body.  The Lancair IO-550 N or G engines I've seen have the fuel flow sensor there (but I haven't seen that many, so I might have seen an unrepresentative sample).  All the fuel that leaves the engine driven fuel pump has no place else to go except through the throttle and then through the spider and then through the injectors and then into the cylinders, since there is no fuel return line downstream from the pump.  Putting the fuel flow sensor between the pump and the throttle body or between the throttle body and the spider would give the identical reading.  There is more room to install it between the pump and the throttle.  Maybe you're thinking of a different engine with a different configuration?

 

Regarding fuel pressure, I'm measuring fuel pressure at the injectors, which seems to me to be the more relevant metric.  This seems to be supported by TCM's SID 97-3 fuel system setup instructions, which says that full power unmetered fuel pressure is shown for reference only and that full power adjustments should be done based on metered fuel pressure.  

 

As a practical matter, except for adjusting the fuel system according to SID 97, I don't think it makes a whole lot of difference if you're measuring metered or unmetered fuel pressure.  If whatever you're measuring suddenly changes, it's worth taking a look to find out what's going on.

 

I'm not an expert on this and hope someone will correct me if I'm wrong.

 

Best,

Dennis