Prostar 190

[k.ripley]

I have a 1994 prostar 190 with the 350 TBI. I have been having a nagging problem with the boat. The engine stutters very briefly at different times of operation. It doesn’t seem to matter if the boat is under load or not, however it usually occurs when not under load (skiing). I have had the boat into the mastercraft dealer in Ontario and in Michigan, and they have done a full tune-up and replaced the fuel pump and throttle position sensor, and this problem still continues. When the dealers have had it, of course the problem does not occur when they are test driving since this stutter doesn’t occur all the time. It also does not seem to matter whether the engine is warm or cold.

Any suggestions of what else to look for/at would be appreciated.

Thanks in advance.

[JimN]

If they didn't find a code for the TPS or test it with a digital storage scope, get your money back for it. They almost never go bad. If they didn't test fuel pressure, get your money back for that, too. Replacing parts because they are suspected, without having been tested is BS. That's for untrained "shade tree mechanics", not franchised MC techs (or any other dealers), who are charging for their time.

If the stutter is not violent, but seems like it could be ignition related, it may be. I have found that the cap, rotor, plug wires and plugs make a big difference- not always due to the brand but the condition. I have seen new boats do this, run for the first time (after the MC test runs) when I was setting them up and re-seating plug wires on both ends, making sure the rotor is on completely and in contact with the button on the cap can cure it. I have seen bad caps, one flaky plug and loose wires cause it, too.

If the cap, rotor, plugs and wires are more than a couple of years old, replace them (with the recommended parts). Using a part that's "close" doesn't work. AC MR43TS plugs, good 8mm plug wires (not a "Make Your Own Plug Wires" kit), a good cap and rotor (I use Borg Warner for my truck. They now have a limited lifetime warranty and when I asked what limits it, he said mainly parts breakage. Cheap cap and rotors should be avoided. Clean the flame arrestor frequently. It's the most neglected part I have seen and I have said this hundreds of times. A cap or rotor may look great but still might not work properly. The coil wire sees a high voltage signal eight times for every rotation, so at 5000RPM, it sees 40,000 impulses. If it's not capable of that frequency, it'll miss at different RPMs, usually some multiple of the lowest problem frequency, which may or may not be in the range where the engine runs.

Running a car or truck at idle- 3000RPM most of the time with the occasional high RPM run is one thing, running at high RPM a lot is different.

BTW- the motor is under load any time the prop is engaged and the boat is under power in water, not only while skiing.

[k.ripley]

Thanks Jim.
They did the cap, rotor and wires when they did the tune up and the stutter is less frequent after all that work. But yes very frustrating I will check and maybe replace the cap. The wires should be under warranty but I would have to take back to the dealer to have them checked. Probably be cheaper to do myself.

[Pete]

Mr. Ripley-

I have the exact same boat/motor. (Awesome to ski behind, none better).

A few years ago I had a similar problem and it turned out to be debris in the screen of the fuel pump intake. I removed the fuel pump and cleaned out the debris, then I installed a fuel filter in the fuel line, before the fuel pump. Just a generic fuel filter from auto parts store. The boat has a fuel filter after the fuel pump which does nothing to protect the fuel pump from debris.

Remove the larger fuel pump line and look into the fuel pump with a flashlight and you will see the debris if there is any in there.

Also, I have a good friend that used to be the lead tech at Watersports Marine in Fenton,Mi (M/C dealer). He is now on his own doing mobile marine service. His name is Bill Allen and his ph# 734.417.3844. I highly recommend you give him a call. He is extremely knowledgeable, thorough and helpful. I would recommend him to anyone and he has helped me a lot with my PS.

Let me know how you do!

Pete

[G-man]

Double check on the spark plugs they used. Use what jimn tells you.