Engine misfiring and alarming

[Loshie1056]

I have a 2003 Sunsetter, 21 LSV with a 335 Monsoon. I posted earlier on an issue I had with poor engine performance and got some good feedback, which I incorporated but now have a new problem. Previously the issue was low power under full throttle, but tended to improve after a while and then seemed fine, until I brought it back to idle then full throttle which was poor power again. The recommendations were to change plugs, rotor, distributer cap and flame arrestor, which were all done. I took it back out on the lake for a shake down and the low end lagging under full throttle was solved and it ran really well for a few minutes but then started miss-firing and alarming. I got a recommendation from Indmar to swap out the ignition module, which I did; took it out today and under low throttle, miss-firing and alarming remained. Thoughts, suggestions, other than taking it to someone who can put a reader and pull some codes, assuming there will be some. 

[martinarcher]

Is it back firing through the intake or just missing?  It would be great to get the codes off the motor.  If it's just missing, I'm wondering if you've got a fuel delivery issue.  Have you swapped/changed fuel filters?  

[justgary]

Does it smell rich at low speed?  You could have an injector hung open.

[electricjohn]

Water in the gas? That's what my 335 did.

[Loshie1056]

11 hours ago, martinarcher said:

Is it back firing through the intake or just missing?  It would be great to get the codes off the motor.  If it's just missing, I'm wondering if you've got a fuel delivery issue.  Have you swapped/changed fuel filters?  

Thanks for the response. It doesn't seem to be back firing through the intake. It is just missing and as soon as it miss-fires it alarms. I haven't changed out the fuel filter but I have good pressure to the injector manifold so I initially ruled that out. 

[formulaben]

1 hour ago, Loshie1056 said:

I haven't changed out the fuel filter but I have good pressure to the injector manifold so I initially ruled that out. 

Was the pressure checked at full throttle?  I would change it just because it probably needs it anyway.  Also, just to remove it from the troubleshooting tree, I'd dump some Heet in there just to be sure.

[martinarcher]

Yeah, good call, a red can of Heet will take care of any water if that's all it is.