I am the happy owner of an LBZ Duramax, fantastic machine, and need some help with my chevy 350 that is in my Mastercraft ski boat, direct drive. The engine cuts out when under throttle. The engine usually runs fine. When it doesn't run fine here is the typical pattern: when I gun it to pull the skier out of the water it goes well for a few seconds then cuts out for a second or so, then re-engages. It does this over and over, coughing and sputtering and either dies or just starts running fine again. If it dies, it starts right up again but surges while idling slightly. It might run fine after quitting or it might do the cutting out dance again. Any thoughts on where to start with this?

 

Sound like it is running out of fuel. Try taking off the fuel filter and blowing through it in the direction the fuel goes. If it is hard to blow through then it is likely your problem.

 

This afternoon I removed the fuel filter and was able to blow through without any obvious obstruction. To clarify (not sure if it will change anything or not), when the engine cuts out it is a sharp cut, no petering out, just stops, then restarts, stops and restarts causing a surging sensation. It will then pop and either die or start running with no further issues...until the next time. If it dies, it starts right back up again and may or may not repeat the above pita process. If you have time, I would really appreciate the next step to take to try and work this out.

 

short circuit? frayed wire? bad kill switch?

 

I will run through the wiring tomorrow after work.

 

I just realized I have a fuel/water separator on my boat, will change that out today too.

 

Today I replaced the fuel/water separator filter, checked the filter at the base of the fuel pump, checked the entire engine for loose wires - and found one that was almost completely separated from the connector...thought I had found the holy grail.

Took the boat out to the lake and it still does the same thing.

What I learned: it takes some time for the cutting out to occur. Driving without the engine cover also allowed me to see that the exhaust manifold gasket is leaking like a sieve at higher rpm...I guess as the water pressure builds to cool the engine it pushes through the gasket (doesn't happen at all at lower speeds or warm up).

Is it possible that the water leaking out of the exhaust is dripping down on the wiring (I believe the ecm is on the starboard side of the motor and gets pretty wet from all the water leaking) and causing a short? I tried protecting the wires with a bunch of shop towels but the cutting out still occurred.

Next step: I am going to take a video camera out to the lake after work tomorrow and post a video of what this engine is doing on you tube to see if this helps any of you give some advice.