502 Mag Mpi Running Bad
 

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:lolhit:

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.

:lolhit::drink:

That was funny I liked it made my morning better Thanks GO4Broke

So changed the fuel/water filter and check the plug and plug wires. Ran good and then out of no where smooth water started doing it again, this time it is doing it at lower RPM'S as well as higher RPM's. I know I need to hook it up to a computer but what stuff can I check til then. I'm thinking about replacing the plug wires in the morning, one of the wires has a tear in it at the plug and has been tapped together by electrical tape. ANY HELP!!!!

you said you had water in the separator. did you drain the tank after you put a new separator on ?

Electrical tape isn't enough insulation to contain 35-50,000 volts! That is likely the whole problem.

Had to put down my so-co and coke to type that.

it is not a complete tear through but starting to come apart, but I am going to start there. Yes drained the tank and fresh gas.

You panicing settle down take a deep breath....... replace all the wires. then when its dark I mean really dark out start the motor and look at the coils see if there arching over . My SeaRay had acouble coils arching over once that caused havoc but spotted the bad one in the total dark that was on a 8.1LS horizon motor

So what did you find??

So after going crazy...My Uncle got into town (has a 46 searay after several upgrades and does all his own MNT, had 454's in his old boat) and we started with the replacing all the spark plug's and wires. Found a dirty contection on the distributor. Still did not fix it. While we were out trying after all that, Trying to pay attention to everything, I noticed that the engine temp would bounce up for about 30 secs to 60 secs and then drop down. That is when I said give me a soco and diet, It was the freakin fresh water intake impeller, engine was protecting itself. Spent 3 hrs pulling the pump out and taking the impeller out and sure enough 1 blade gone and several others going. Replaced it and runs like a dream. Ran for three days and got a "pin" hole leak in my power steering fluid hose... Said enough is enough and took it out of the water and trailered it home to Dothan AL. Took the hoses off tonight and getting two made tom. Be running in Destin or the Chattahoccee River this weekend. Thanks for all the tips