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Message
Here's a nasty failure mode to watch out
for.
After fitting a new fuel pressure sensor I
turned on the pump to check for leaks. The sensor fitting was good, but there
was a slight smell of fuel which I traced to the regulator. There was a very
slow drip which stopped after a few seconds. I stripped and rebuilt the
regulator. Next pre-flight I pressurized the system and checked for leaks with a
flashlight. The main return hose from the rail (steel braided teflon 1000PSI)
was a little wet. I removed the cowl and turned on the pump. No leaks. I removed
the hoses from the regulator and pressurized the entire rail & hoses to
100 PSI. The pressure held for more than 10 minutes. I put it all back together,
re-installed the cowl and tried again. No leaks. I left it overnight, then did
another check with the pump on. I had a steady drip from one hose that stopped
after a few seconds. I ran the engine and did some taxiing, then checked again.
No leaks.
Next day I did another preflight check with
a flashlight. Again the hose was a little wet, but the leak went away after
a few seconds and the hose dried out. After removing the cowl there were no
signs of a leak. Last night I checked again. This time I had a jet of fuel
from the middle of the return hose. I removed the braided teflon hose to
find a dark spot at the point of the leak. The hose had not been rubbing on
anything and was not abraded. The damage looks a lot like the result of an
electrical arc, but there's nothing for it to short to anywhere near.
My theory is that this hose carried cranking
amps at some time or other. I'd swear I've never cranked the engine with the
ground strap off, but this is the only way I can imagine that his damage
occurred.
Anyone have a better theory?
John (checking my other
hoses)
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