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The low pressure pump would not be able to produce 25 psi at low rpm... But to verify which pump is installed is an easy visual. The high pressure pump has a wave like ring washer around the bottom of the pump between the screw heads that hold the pump together and the pump body and the low pressure pump has no wave washer between the screws that hold it together and the pump.
If you are a member of the yahoo Lycoming group at the bottom of the files section there is a picture of the two pumps side by side. https://groups.yahoo.com/neo/groups/lycoming/files It does sound as though there may be a blockage or a leak causing the FP to deteriorate as demand increases. Good Luck, Mahlon Quote:
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Today I had another look at the pump. There is no part number on the pump but it has the wave like ring washer at the bottom. I prepared an aux tank which will eventually go in the rear baggage area today and I will connect the tank to the inlet of the engine driven pump and will see how the pressure develops. That way the pump doesn´t have to suck through the boost pump.
Mixture control is unresponsive til cutoff. I´m interested what timing numbers are best for the IO-375, and yes I adjusted to 25 deg. On my -7 with an IO-375 this worked out ok. |
Update - problem solved
I connected the aux tank to the engine driven pump inlet and the engine was running on full power with 25 psi and 17 GPH. Then were is the problem behind the firewall? Well I removed the boost pump and made a connection between the fittings and the engine was running fine again. So the boost pump is faulty and restrictive, blowing into the inlet proves clearly the restriction.
Idle is much better now. I had to enrichen the idle mixture quite a bit and it started to smooth out. |
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Good point with the suction leak. I might check but I really think the boost pump is the problem. Two reasons: I should smell fuel with the boost pump running - ok only if there is a leak downstream of the pump. The other reason should be the final answer: I replaced the boost pump with a piece of hose and the engine is running fine; and blowing into the boost pump inlet shows the flow restrictioin.
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