Got the boat three days ago 1998 Sonic Prowler 502 MAG MPI, and already having problems. Boat ran strong and great on a 45 min sea trial. Got the boat home and ran a good weekend until I hit some pretty good ways giving the boat a good workout. After hitting the first few rollers the boat started to miss. after about 20 to 30 minutes of working the throttle I finally got the boat up and running without missing, this was in calm water. Ran for the rest of the day no problems, but was calm water. Today get the boat out and run a good 10 minutes calm water, no problems, then pass a 50 footer throwing some good rollers and as soon as I hit them engine starts missing. When I say missing I mean it will not get over 3000 to 3500 RPM, and you hear the motor "choking" out. Strong smell of gas out of exhaust. As long as the water is calm no problems but as soon as I hit some waves the motor starts choking out. PLEASE HELP!!! point me in the correct direction. Check plug wires, GOOD, checked fuel/water separator, GOOD. It is just crazy that it only does it when you hit rough water.....

Possibly a Fuel pressure problem or a restriction in the tank for your fuel supply...LT

Have it scanned for codes.

First check the main wiring plug on the back of the engine. Undo the clamp, remove plug and reset.

I had issues with my 502mpi's that ended up being sensor related. When I finally blew it up I switched to carbs. I'll see if I can find the paperwork for what was done to mine.

But in the mean time find someone you trust to scan for codes and see if they are willing to go out with you with the scan tool.

I like Carbs too hit it with a hammer and it will get you home

x2 on checking the main plug. There may also be water in the bottem of the fuel tank. take a fuel sample and check the fuel pressure, especially if you can do it while its running bad.

My first bet is the plug though.

Float is cracked and has sunk. Very common problem.

Put down the vodka and cranberry, its a 502mpi, no carbs.

I replaced the fuel/water filter this morning and dumped the contents into a clear container, and I had water in the fuel. My first ROOKIE mistake was the first time it happend raising the hatch and letting someone else check all the plug wires, of course they said "they are all fine". While changing the filter I went all around the engine checking the wiring and sure enough a plug wire was completley off of the plug. put it back on and running good, although it was calm water, and when I say calm I mean glass (on the TN river). The real test will be this weekend when the big cruisers get out and it gets rough. I believe that was the problem though. Thanks for the input, Ill post the results of the weekend hopefully good with no problems. If it starts again I will just have to wait until I can get plugged up to the computer back home, thinking it will be fuel pressure.