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912iS Increasing fuel pressure (approaching 50 PSI)

edmondthx1138

edmondthx1138

Member
I've noticed for the past few months my fuel pressure rising from flight to flight. Usually pressure is at app. 43.5 with both pumps running. Engine runs fine, power output normal, etc.
I'm getting ready to change coarse and main fuel filters in a couple of weeks as part of condition inspection. Other than clogged pumps, any other reasons for this?
 
Fuel pressure is controlled by the pressure regulator. It could be a regulator issue or the bypass fuel line to the tank having an obstruction. The symptom for a clogged filter or pump would be lower than normal pressure.
 
Because the fuel pressure sensor is between the pumps and the fine filter, the rising pressure reading could be an early warning indicator that the fine filter is beginning to clog. The pre filter is before the pumps so yes if it was clogging the pressure would be lower than normal.
 
Last edited:
jrtens said:
Because the fuel pressure sensor is between the pumps and the fine filter, the rising pressure reading could be an early warning indicator that the fine filter is beginning to clog. The pre filter is before the pumps so yes if it was clogging the pressure would be lower than normal.
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THIS^^^^^^^

Additionally, the engine documentation specifies that the fuel filter be changed after the first 100 hours of operation. This is because when the fuel pumps are new, they can release small wear particles as they break in. After 100 hours this should no longer occur.
The recommended filter change is why a second filter is supplied with the new engine.
 
Try a manual fuel pressor gauge on the ground and see what the pressure is reading. (Some auto parts stores have them available for rental ) My VDO sending unit was beginning to fail and started reading high, setting off an out of parameter alarm. I was able to run the pump and engine both on the ground with it connected, compare readings to the digital output and saw it was elevated compared to the mechanical gage. Replaced the VDO sending unit and am back flying with confidence.
 
edmondthx1138 said:
I've noticed for the past few months my fuel pressure rising from flight to flight. Usually pressure is at app. 43.5 with both pumps running. Engine runs fine, power output normal, etc.
I'm getting ready to change coarse and main fuel filters in a couple of weeks as part of condition inspection. Other than clogged pumps, any other reasons for this?
Click to expand...
See Maintenance Manual page 13-14, paragraph on changing fuel filter
 

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edmondthx1138 said:
I'm still changing the fuel filters this week as part of the condition inspection.
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You don't say how many hours are on the engine.. but while you're back there, check/clean the Andair screen filter. Its inspection was left out of the Maintenance Manual schedule/checklist and often goes unchecked. (not the cause of your problem, but since you're monkeying around back there anyway).

The main filter is top of the list. If the pressure across the filter exceeds "12-17 psi" (blockage), then the bypass valve opens and allows unfiltered fuel to the engine. The second item on the list may be to remove the fuel pressure regulator on the engine.. There is a screen filter in it as well which is almost always clean since only (usually) filtered fuel gets to that point.
 
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