Yep...just noticed that, thanks.
With the throttle closed at idle, one instrument indicating fifteen inches and the other indicating higher, suspect the higher one, especially when they're both showing the same RPM.
Remember that gauges seldom indiate correctly. A check of the manifold pressure gauges for proper calibration, for example, will generally show them off by a given value on almost any aircraft. Likewise, the RPM is often not what's being read, and the error changes throughout the indicating range. Checkin that calibration is also wise, but seldom done. Several things spring to mind here. One is a leaking alternate air induction door. You should be seeing a very lean idle mixture of that's the case, whereas fuel increase isn't occuring due to throttle positioning. Perhaps it's just a weak door that's being overcome by turbo induction; in automatic doors this could be simply a weak or missing magnet. It may also be the case of an open overboost valve, or a sticky one, though this normally means a mismatch in the boosted range (eg, above barometric pressure, such as above 29"-30" at sea level).
The engine induction on the 520 involves rubber couplings that are hoseclamped, and leakage isn't uncommon. Leakage symptoms vary depending on where in the system they occur. The rubber coupling hoses tend to take a set, and generally must be replaced if they leak. The common fix is to tighten the clamps, though this seldom works for long, if at all. The leakage checks are done using a vacum cleaner and soapy water, or in some cases, talc. Other problems may also exist.
In any event, until the system is inspected, and the cause determined and fixed, the engine shouldn't be operated in flight.
With the throttle closed at idle, one instrument indicating fifteen inches and the other indicating higher, suspect the higher one, especially when they're both showing the same RPM.
Remember that gauges seldom indiate correctly. A check of the manifold pressure gauges for proper calibration, for example, will generally show them off by a given value on almost any aircraft. Likewise, the RPM is often not what's being read, and the error changes throughout the indicating range. Checkin that calibration is also wise, but seldom done. Several things spring to mind here. One is a leaking alternate air induction door. You should be seeing a very lean idle mixture of that's the case, whereas fuel increase isn't occuring due to throttle positioning. Perhaps it's just a weak door that's being overcome by turbo induction; in automatic doors this could be simply a weak or missing magnet. It may also be the case of an open overboost valve, or a sticky one, though this normally means a mismatch in the boosted range (eg, above barometric pressure, such as above 29"-30" at sea level).
The engine induction on the 520 involves rubber couplings that are hoseclamped, and leakage isn't uncommon. Leakage symptoms vary depending on where in the system they occur. The rubber coupling hoses tend to take a set, and generally must be replaced if they leak. The common fix is to tighten the clamps, though this seldom works for long, if at all. The leakage checks are done using a vacum cleaner and soapy water, or in some cases, talc. Other problems may also exist.
In any event, until the system is inspected, and the cause determined and fixed, the engine shouldn't be operated in flight.
