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Last seen: 6 months 1 week ago
Joined: 08/19/2019 - 05:39
30-0300 with LSU 4.9 Fail in Marine use

I just installed my setup this week and ran it successfully in my yard 2 times.  I was able to head out in the boat one time.  I'm running a carbureted chev 383, with an extra tall and long riser to help keep water out of the exhaust stream.  I placed the sensor in my cold water jacketed exhaust just outside the manifold, about 15  to 17 inches from the exhaust valves.

It ran well, showed me that I have a rich idle, almost stoich cruise of 13.8 to 14.4, and 12:1 on the secondary barrels.  All good, I was thinking.  Then we sat for a while  engine off, with the boat in the lake, for an hour or so. At the next start I got the full lean code.  Tested it today with some brake clean, no good.

Would there be the possibity that 10.5:1 idle fuel contributed?  Or is it more likely water was in the exhaust, or perhaps exhaust temperature?  Water will "wick" along cold metal. There is every possibility that the moisture crept up from the exhaust outlets as I sat and the metals cooled.   Also, the sensor is admittedly not tilted, the people that installed it did so before I ever saw your recommendation to put them in around 12 degrees above flat. 

If needed I can install a timer to delay sensor turn on.  But I'd want to know that it might be a help before going through the effort.

I'm also thinking I may get a 90 degree bung extension and clock it so the sensor faces the right direction down.  That would pull the sensor back away from the hottest exhaust plus keep the sensor from trapping moisture.

Boats run under load at all times, so when I was cruising it at 3000 rpm and 14:1 the exhaust could have been quite hot despite the water jacketed manifold and riser.  Many guys on offshore only like to go 12:1 and such on their big blocks.

Worse case scenario, I can set up the engine and then remove the sensor.  I can do that since my dinosaur doesn't use the sensor or meter to run.  Just to get it right.