Loss of power and dies...HELP!

[tartan30cirrus]

HELP! New A4. Just commissioned it. Motoring along at 15/1600 RPM. Was noticing more vibration from shaft/engine area than I noticed last year. A little later the RPM started steadily dropping and we were slowing down and I turned the engine off before it shut itself off. Back at the dock she starts fine but hesitates...pulling the choke causes the engine to die. Pulling choke partially doesn't seem to have much of an effect. But I was tired and frustrated so I can try to diagnose more tomorrow with some help from folks, I hope. One piece of info that may be important is that I was struggling to get out of the slip against a wind and not hit boats. So I was putting the engine in forward then reverse then forward. I wouldn't say slamming it into gear back in forth but pretty abruptly at moderate RPM. Other info...the temp guage indicates a quite cool temp...really well below 140. She is FWCed. After the incident the temp was much higher maybe 160/170. The gear box felt hot (normal?). Also the oil pressure is 20 under cruising power and a little under 40 idling at the dock. I noticed these things last Fall and had my mechanic check things out but he did not notice anything unusual.

At commissioning she ran beautiful. This is out of the blue and worrying. Please help. I'd like to start troublshooting tomorrow. I can answer questions here to help you help me. Thanks in advance! I'd like to solve this myself.

Cheers,
Clint Chase

[Don Moyer]

Clint,

Is it possible that something wrapped around your prop shaft? Other than that, I'd remove the plugs and do a quick "thumb check" of the compression in each cylinder.

Don

[tartan30cirrus]

Did a load test today at the dock and no problems. Engine started fine. I will check for something around prop. What if a little water got through the fuel line? I will also check compression, but everything seems fine now.

Yesterday I limped home under power. What seems to be going on is the oil pressure (at 35 @ idle) is dropping to just over 20 under cruising power but after a half hour or more drops below 20 and the engine shuts down. This happened twice on the way back to my home mooring last night. When I let the engine it starts fine, sounds fine, and runs with appropriate power, but the oil pressure starts dropping again to what appears to be near 0 and the engine loses its power and shuts down.

In the manual this appears to be #3 on p5-7 "If oil pressure drops to zero very suddenly" but I feel it is not VERY sudden and the oil pressure does build up again but not to above 20 unless it sits overnight. Should I proceed with the corrective actions under #3 in the manual? (I am concerned that note 2 applies since this is a new engine).

Cheers,
Clint

[bcooke]

Hey Clint,

Does your engine have an oil pressure safety switch? I am thinking if the oil pressure drops below the trigger level for the switch, the switch could be shutting off the ignition or electric fuel pump (depending on the setup - I have seen both) thus the engine quits.

In my experience, oil pressure should be lowest at idle and increase to max. pressure as regulated by the oil pressure adjustment fairly quickly as the engine (and oil pump) picks up speed. Since you seem to be having the reverse indications an oil problem could be the culprit. What kind of oil are you using? Could it be contaminated? An oil with too low a viscosity could lead to low pressures when the temperatures come up. I would think a faulty oil pressure regulator would either work or not and wouldn't be degrading slowly over time.

The only other oil related thing I could think of was a small internal leak. As the oil warmed up and became more viscous, it could exploit the small leak more. As the temps came up the gap resulting in the leak could also be increasing, leading to a greater flow at the leak and lower oil pressure. The leak theory is a huge long shot though and I wouldn't chase that one down until you are certain that decreasing oil pressure is the culprit.

Loss of oil pressure can be quite serious as I am sure know and a seized engine is expensive to repair. You might try a direct reading guage on an oil port to verify the oil pressure before going too much further. Indication errors are pretty common on engines in general.

-Britton

[dtinder]

Pls do not ignore the possibility of an intermittant failure of this switch--regardless of oil pressure. At the risk of being cast into purgatory along with burned-up A-4's----they do make these switches with a lower disableing range; ie, 3-5psi, 5-7psi, etc.