2005 VLX has top speed of 13! It's not a TUNE UP!

[devildds]

I have a 2005 VLX Monsoon engine.  I am not a DIY guy when it comes to engines.  I've had a couple of boat shops in my area each do successive tune ups not listening to me when I say it doesn't need a tune up.  I was hoping I could get some direction on here to help me point them in the right direction.  There are no starting issues, idling issues or even top speed issues...until there are.  We can use the boat at cruising speeds for ~30min (all gauges on the dash read normal), and then, all of the sudden, the engine will start "missing."  I'm not sure of the correct terminology so bear with me.  I can run the boat up to about 13 mph just fine, but as I try to get faster than that, it starts missing again.  If I back off at 13mph or below it acts just fine.  I've tried to gun it when it starts missing and it sort of backfires and really seems to choke out but not off--and again, it will work at 13mph or below.  As I've said, I've had 2 tune ups in the past year which haven't done anything for the issue.  Thank you in advance for your advise and expertise.

[justgary]

Currently discussing this very same issue, except your fuel pressure should be 4 Bar (~58.8 PSI)....

In your case, did any of these tune ups include new plug wires?  I would start there if the fuel pressure is OK.

[csleaver]

There are four things I initially check to help diagnose running issues: cylinder compression, the condition of ignition components, fuel pressure, and ECM fault codes.

[devildds]

Thank you all.  

 

My acceleration is perfectly normal.  Again, it usually runs without issue if we're just cruising over to someone's house or a few quick pulls on a wakeboard (load doesn't seem to affect it).  It just gives up after a while without warning. 

I'll ask the shop about those 4 items on your checklist csleaver and the status of the plug wires and fuel pressure justgary.  Thank you all for any input.

[BlindSquirrel]

There is a video in this thread... does your boat do this when you gun it? The one in the video would back fire on occasion too. 

Does your fuel pump make a whining sound when you go to start the boat? 

 

[devildds]

No whining.