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PA31-350 fuel pressure problem. Help!

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New Member
Aug 20, 2011
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I work at a charter company and we are currently having some troubles with one of our Chieftains. A few weeks ago it came home and was snagged as low fuel pressure at idle. We did our ground runs and it turns out the engine won't idle without the electric boost pump on. When we shut off the electric boost pump, fuel pressure drops off well below the red and the engine sputters and spits and won't stay idling.

We changed out the engine driven pump (three times), and each time it "seems" to fix the problem, but it comes back again shortly after, so we can safely say we don't have an engine driven pump problem. We've tried starting each engine with the other engines boost pumps with the cross feed on, and the problem stays with that engine and doesnt follow to the other engine. We've tried adjusting mixture, which didn't help. We've also learned that it only happens once the engine has warmed up, and as soon as we throttle past 1000 RPM, the fuel pressure is perfect and the problem disappears.

Weve been wracking our brain on this one and just want to make it go away! Does anyone have any suggestions or has anyone seen this problem before?

Engine: Lycoming TIO/LTIO -540 J2BD

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