REFLECTOR: Engine failure causes

[Al Gietzen]

I too have injection and a return line. Airflow performance built my fuel
pump setup (2 parallel electric pumps) but the return line does not go back
to the sump. Instead it feeds right back in before the pumps. They say this
keeps the flow up but avoids fuel frothing. 

Kurt;

I think there may be two potential issues with this; one is that any bubbles
(foam) that form happens at the exit of the regulator. Now you're feeding
those bubbles back into the pump, which is OK since it will collapse them
again - up to a point.  Which relates to concern #2; running that same fuel
around the loop heats it up, and along with incipient bubbles already coming
in before the pump, aggravates potential for vapor lock.

I also have another filter just before the pumps.

This would be concern #3.  A filter before the pump is a restriction to the
flow; especially when it gets some debris in it.  That's asking for vapor
lock.  We want easy gravity flow to the pump at all times; unless the pump
is in the tank.  Especially since you have sediment filters in the line to
the sump (which probably have screens in them?), and the sump is a big
sediment trap; no need for filter before the pump.  Put a good 15-30 micron
filter downstream from the pump, and the fuel pressure sensor downstream
from that. Then if the filter ever gets dirty you see a bit of reduction in
pressure, but you don't get surprised by a vapor lock and engine stall.

FWIW,

Al

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