Indmar Assault CAT 350 dies/ Runs rough

[SupraCLT]

Ok, I am casting my fate on the intelligence of you fine folks... I am hoping SOMEBODY on here has had a similar experience to what I am dealing with. This summer has been nothing but a comedy of errors for my boat so I'll try to be as succinct as possible. Starting about 8 weeks ago I've had intermittent issues with the boat dying or running rough. At first I thought it was due to the two bad batteries I had top of the season but the electrical issues cleared up and the starting/running issues did not. They've continued to worsen in fact. I've listed the symptoms below
-Stubborn to start. Starter motor runs but engine doesn't catch, or catches then bogs down and dies.
-Runs rough then dies... Once I get the boat started it doesn't want to run smooth at Idle. If I can get the REVs up (transmission disengaged) it seems to run fine.
-Engine cuts off while running. Without showing any warning signs (dips in REVs, rough running etc..) the engine cuts off when running. The computer stays up so this doesn't seem to be computer/electrical
-The issue is not consistent or reproducible on demand. Some days it turns over and runs fine first attempt, other days I cannot get it to start
-Once it dies, it needs to sit for several minutes before it can start again.


I have tried several things to fix the issue:
-Ran sea foam through the motor
-Used Stabil on the last 2 tanks of gas (its been going on for about 2.5 tanks of gas)
-Had the boat in for "annual maintenance" which replaced plugs, wires, fuel filter as well as oil and fluids. Boat tech wasn't able to reproduce the issue.


Two weeks ago we went out and surfed for about 3 hours, it died about 100 yards off the dock, but once we got it re-started it ran 3 hours and died once for 10 minutes or so.

This past Sunday it started right up, ran for an hour or so but then died 4 times.

I am about to send it back to the marina but would love to give the tech some informed direction vs. him billing me multiple hours for "diagnostics."

this boat is a 2010 with ~170 hours on the motor... bought it last year with 140 on it.

Any and all thoughts would be appreciated.

[tretter7]

So you have a fuel delivery or spark issue, and you need to isolate between the two. When it dies while running is it a complete and total die - no coughing or sputtering? When you try to restart it will it cough/sputter at all or it's just totally dead? Bring a spark tester with you next time you go out and when it dies, put the tester on and try to restart -- see if your're getting spark.

[Sirgonz]

check the coils.... sometimes they can be intermittent and random

[SupraCLT]

So you have a fuel delivery or spark issue, and you need to isolate between the two. When it dies while running is it a complete and total die - no coughing or sputtering? When you try to restart it will it cough/sputter at all or it's just totally dead? Bring a spark tester with you next time you go out and when it dies, put the tester on and try to restart -- see if your're getting spark.

When it dies it is a complete and total die, feels very binary (on then off.) Trying to crank it back up immediately gets you a grinding starter motor and thats it. Then about 5-10 minutes later (not predictable) you can try to crank it again and you'll get the cough/sputter when it tries to catch. I'll look into the spark tester....

Boat tech is supposed to be putting the boat on the rack and letting it run (on a fake-a-lake) to try to reproduce the error after the failed on-water test. Fingers crossed. He is confident its not the pump at this point as PSI was strong through the on-water test. I also asked him to check the spark to make sure it was firing correctly.