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Intermittent No-start when warm

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I really enjoyed the quest-for-the-cause test we had here a while back for a mechanical problem and offer the following to y'all as a second course. After a year and a half of chasing a solution, I finally have one -- but I'm curious, what would you do?

Here's the problem:

1998 Monsoon 325 EFI, approximately 400 hours on her.

ALWAYS starts right up when cold and runs very well and strong.

SOMETIMES (maybe 4 out of every 10) on restarts to change skiers or boarders it will refuse to start. It will crank strongly for a long time but but never come close to firing. Only way to start it is to pull the neutral knob and to crank with wide open throttle. It will start but there are copious amounts of black/grey smoke for a bit and it runs at a high idle for 20-30 seconds then settles down into normal running.

Ok team, GO! How would you solve this problem?

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Good start. Basis stuff I learned here, I replaced the fuel filter. Then I learned more and found out I had 2 filters (who knew) and replaced the second. I even went so far as to read my manual and realize that I should really be burning 89 octane vs. the 87 I had been using.

All those changes equated to no improvement and a higher gas bill.

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my 04 hh needs turning over more when it is warm, starts instantly when it is cold. the prob with your boat is that it is running rich, which it needs too when cold, but not when hot. if it were a car i would check the o2 sensor, i don't know the boat equivalent. obviously there is no choke, but the computer is sending it too much gas.

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I was told that there is a fuel screen in the injector line also. I'm not quite sure, but if fuel is monitored by the computer and it thinks it is starving for fuel, won't it open the injectors up (rich) to give it more fuel, virtually flooding out the engine

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Mr. Speck is on the right track but why? It is definitely running way too rich as witnessed by the totally black and nasty looking spark plugs. But what is causing that situation?

Galaxy Toad Eagle Driver consuled to check and/or replace the cap and rotor. Duh, I never even thought of that. Opened the cap up and found a very corroded mess. Yuck. How could it still be running? That MUST be it. Replaced those parts and in my mind it ran better, but not in reality.

Now what?

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Peter Smooth, you win the prize!

The water temp sensor is exactly what was causing the problem. When they put it on the computer at the shop the sensor was giving readings all the way down to -17F, which, if true, would have meant I had serious other problems.

Bottom line, changed the sensor, cleaned up the contacts to it as well and for the first time in 1.5 years I have a totally great running BU. My fuel consumption should drastically improive as well.

What prize does he get Tracie??

ps. Many thanks to Galaxy Toad for his many suggestions along the path. He almost got me there.

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I have seen this also when the thermostat sticks open. Boat runs in cold start mode all the time. You can even start gaining oil. Good call Peter.


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  • 1 month later...

I also have the same problem baddog had, except mine will fire then just shut off. It even happened to the dealer during the 20 hour service. Just like baddog said, only when warm, maybe every 6 -10 starts, but very intermittent.

2005 Sportster LX

LS1 engine

25 hours

Had this problem since new. Dealer can't figure it out. Indmar hasn't come up with an answer, Malibu is trying to help but no answer yet.

Calibration re-set

IAC replaced

Water temp sensor replaced

t-stat replaced

Lanyard switch replaced

Anyone have any other suggestions?


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I think the dealer (and Indmar and Malibu) were trying everything they could think of before replacing the ECM. Guess that will probably have to be what's next.

Hadn't thought of the muffler bearings. :)

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It was actually the Malibu factory that suggested replacing the lanyard switch. It sounded crazy to me, but they said they had a batch of bad switches that were causing intermittent starting problems. So I guess that one was just to be sure it wasn't one of the bad switches.

Today the factory called me again to say they were "discussing the matter" with Indmar and would get back to me. Not sure why they don't just replace the ECM at this point.

Another interesting point the factory raised at the very start. They asked if I had installed any insulation under the engine cover. ( I hadn't) Apparently on some boats this has raised the temperature under the cover enough to cause problems. FWIW

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  • 1 year later...

After another year of trying to solve this problem, finally the answer. The prize for this round goes to Sunsetter95. Turns out there is a screen in the fuel pressure regulator that was restricted enough to cause the intermittent "too rich" condition. Apparently, if the gas tank is not thoroughly cleaned at the factory, bits of fiberglass, etc can easily plug this screen. Even though the fuel filters were obviously in place and changed while searching for the cause, this screen is very fine and easily plugged.

Hope this helps someone else with this problem. :)

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Yeah, I'm glad the dealer finally found the problem too. It only took two years with both the factory and Indmar suggesting many possible sources for the trouble.

I don't have a shop manual so I can't tell you exactly, but the dealer said the screen is in the fuel pressure regulator. I imagine the location of the regulator may vary on different engines.

I'm planning to pick up a manual and if its not too big of a job, I will clean this screen annually with the regular annual service. However, the engine has always ran great after it starts, so I guess if this screen is not restricted enough to affect starting, then you'd probably never know if it was restricted at all.

Maybe someone else can shed more light on this.

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