John Deere internal fuel leak

[Mr Mower Man]

I have a John Deere LX280 in the shop, engine is a FH580V-BS04. The crankcase oil level increases while the engine runs, the customer says, and after sitting in my lot for a week, the oil level went way up, and it’s obviously a crankcase full of gas. I remove both valve covers, and gas dumps out of them (that’s how high the level in the crankcase was). My first thought was the fuel inlet valve in the carburetor leaking gas through. However, when I ran the engine last week, it didn’t run rich at all. And when I separated the carburetor from the intake manifold, it looked dry like it should be, not having gas running out of it like I would expect if the carb was leaking gas into the cylinders. Then I started wondering if the fuel pump was dumping gas into the crankcase through the impulse hose. This fuel pump can be disassembled, so I removed the 4 screws to inspect inside it. The “dry” side of the impulse diaphragm was very wet, and it should be dry, right? I didn’t notice a hole in the diaphragm, but how else would it be so wet in there, and inside the impulse hose as well? I did not run the engine since last week, only turned it over a few times to see the fuel pump work. So I’m guessing the fuel pump slowly siphoned a bunch of gas into the crankcase during the past few days, and if I replace it, my problem goes away. Sound reasonable to you guys? Or am I missing something? Thanks!

[bgsengine]

Nope sounds perfectly reasonable and in fact the most likely thing. Only way for gas to pass from wet side to dry side would be through the diaphragm, or a leaking gasket - Hold diaphragm up to a strong light and look through it, you'll likely spot the porosity.

[bobodu]

Yep....fuel pump making oil.