99 ski nautique feels like it's misfiring

So we use a 99 SN with the 5.8 engine used solely on a slalom ski lake and generally take it out every Saturday and Sunday during the ski season. We noticed at the end of last season the engine was starting to misfire ever so slightly especially on initial takeoff.

At the beginning of this season the plugs, wires, cap, and rotor were all replaced. This didn't really help at all but the miss was still faint and not really that noticeable so we thought maybe the missing we were still feeling was in our heads. Fast forward to mid season and the miss has gotten more noticeable especially at slower speeds like 28mph and slower. We decided to replace the coil thinking maybe that's the issue and if anything that made it worse. Checked fuel pressure and it puts out a steady 32psi at idle on the rail and if we unplug the vacuum line to the fuel pressure regulator, it goes up to 40psi. If we rev the engine, there is a quick dip in pressure and then it stabilizes. Those pressures seem normal from what I've read but I'm not sure because different people are saying different things. Today we decided to change the plugs again just because they're cheap. The boat misses so bad now at all speeds that it's starting to raise concerns that we may be hurting the engine.

Any ideas what else we should be looking for? We haven't tried to pull any ECM codes but the check engine light isn't on and the light does work.

gt40KS wrote: Hi John, Guessing you have the GT40 since you speak of an ECM at the end. As Ken is prone to quoting, when you think it's fuel it turns out to be electrical and vise versa. On that note, strangely, the issue of a bad PIP sensor in the distributor has come up a few times lately.   Only takes a few minutes to pop off the distributor cap and check the PIP - it should not move at all. Just a little wiggle can cause uneven idle and very slight missing, almost undetectable at higher rpm's as I recently found out. Others have found a rusty mess that moves all around to the point the engine will barely stay running. But of course, this is just one scenario. Unfortunately whenever you start adding technology problems will inevitably become more complex.

Yes it's the GT-40. Doesn't sound like an expensive fix but a little bit time consuming. It might be a little while before I can experience if this fix will work since I'll be out of town but I'll forward the information on to my ski buddies.