If your engine is having intermittent fuel flow issues, runs better on
the left tank than the right, and gets better when the electric boost
pump is turned on, would you suspect that the electric boost pump is
the problem? We certainly did not, but that was precisely the cause.
The plane, a 1975 Arrow II with a mid-time IO-360, was indicating sporadic
fuel flow and low fuel pressure, to the point of engine roughness, that we
attributed to a faulty mechanical pump because it would always run normal
with the electric boost pump on. After replacing the mech pump, the symptoms
actually got worse. We replaced the fuel controller, some lines, and the fuel
divider to no avail. Bench checked mech pump, it was good. Because engine would
run better off the L tank, we pulled the R tank, inspected it and the line
connections, also to no avail.
New symptom appeared that during taxi the engine would occasionally try to quit
during turns, with fuel tanks full. Reinspected both tanks, nothing found.
We did a vacuum check on the lines, found a couple of small vacuum leaks in the
selector valve and the gascolator. Replaced both of those, did not fix the issue.
Finally got to the point where we had replaced or inspected everything in the fuel
system except the electric boost pump. We disconnected that, spliced a line around
it, and lo and behold the engine ran perfectly. Installed a new boost pump and now
runs fine.
Upon inspection of the boost pump, a spring loaded piece inside had become worn and
would intermittently move out of position enough to impede flow. Turning on the pump
would reset the piece to it's correct position. Feeding from the R tank would aggravate
it because of the longer distance thus higher suction to draw fuel from the tank. The
condition worsened to the point that the loose piece would shift during taxi turns,
again impeding fuel flow. We have flown ten hours since replacing the boost pump and
the fuel flow issue is completely fixed. Frustrating as it was, at least we now
have a "new" fuel system that should serve us well.
the left tank than the right, and gets better when the electric boost
pump is turned on, would you suspect that the electric boost pump is
the problem? We certainly did not, but that was precisely the cause.
The plane, a 1975 Arrow II with a mid-time IO-360, was indicating sporadic
fuel flow and low fuel pressure, to the point of engine roughness, that we
attributed to a faulty mechanical pump because it would always run normal
with the electric boost pump on. After replacing the mech pump, the symptoms
actually got worse. We replaced the fuel controller, some lines, and the fuel
divider to no avail. Bench checked mech pump, it was good. Because engine would
run better off the L tank, we pulled the R tank, inspected it and the line
connections, also to no avail.
New symptom appeared that during taxi the engine would occasionally try to quit
during turns, with fuel tanks full. Reinspected both tanks, nothing found.
We did a vacuum check on the lines, found a couple of small vacuum leaks in the
selector valve and the gascolator. Replaced both of those, did not fix the issue.
Finally got to the point where we had replaced or inspected everything in the fuel
system except the electric boost pump. We disconnected that, spliced a line around
it, and lo and behold the engine ran perfectly. Installed a new boost pump and now
runs fine.
Upon inspection of the boost pump, a spring loaded piece inside had become worn and
would intermittently move out of position enough to impede flow. Turning on the pump
would reset the piece to it's correct position. Feeding from the R tank would aggravate
it because of the longer distance thus higher suction to draw fuel from the tank. The
condition worsened to the point that the loose piece would shift during taxi turns,
again impeding fuel flow. We have flown ten hours since replacing the boost pump and
the fuel flow issue is completely fixed. Frustrating as it was, at least we now
have a "new" fuel system that should serve us well.
