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I need a motor/mechanical genius....

 
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DJBusyB
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PostPosted: May 26, 2014 12:32 pm    Post subject: I need a motor/mechanical genius.... Reply with quote

I have a 2001 Calabria Sport Comp VTS, with a Mercruiser 350 MAG MPI engine. This season I've been experiencing a problem, that my maintenance shop can't resolve. After having it in the shop, the reported that after running the engine for an hour, they still couldn't get it to produce the same results as I described.

When I first drop in, the engine runs fine, idles well, and runs like it should, and has in the past. The first time I went out, it started exhibiting these symptoms after about an hour, and now it does so after maybe 2 hours.

After time has passed, the idle will start to drop down between 500-600 rpm (according to my Perfect Pass). I'm accustomed to it idling between 600-1000 rpm, normally. When I put engage the idle gear position, the boat will idle forward, but on occasion, the idle will drop, and if I put it back to neutral it will idle back up, but on occasion will just die.

When this has been happening, if I try to throttle up the engine, the engine will start to die, and when it finally decides to give up, it sounds like it is sucking every bit of air in, as if it is starving for air. If anyone knows the term 'dieseling', that old cars used to do, that is almost the type of symptom it is exhibiting, while the key is still engaged.

Today, I was able to get past this idle-to-die condition, but engaging the gear, then quickly throttling up and down, until the engine seemed to run fine. While we were cruising along around 30 MPH, all of the sudden the engine just sounded like it was bogging down, and my speed dropped, rapidly. I could put it back into neutral, then the engine would idle. I could repeat throttling up-and-back until it would engage the engine just fine, but then after cruising along for another minute or two, the engine would bog down again.

I've tried to get video of this, the last time I was out, but didn't do so today. As stated, my mechanic said they'd be glad to take it out on the lake for a couple hours (at $95/hr) to see exactly what is happening, but I'm sure I'm just missing something.

The first time out, in April, we were able to engage the idle gear, and limped back to the dock. Suspecting water may have been in my fuel tank, I bought 2 cans of Seafoam, based on some other research, then ran my engine for about 30 minutes at the house, even tilting my trailer to move any possible water to the back of the tank, into the lowest point. After another time out, with the same results, I luckily had a friend riding in his boat that day, and he towed me back to the dock. This is when I took the boat to my mechanic, and even bought 2 more cans of Seafoam after they couldn't determine why it was doing this.

Just before we went out this weekend, I decided to add Premium gas to my tank, to see if that would help.

I have a 65 gallon fuel tank, and wonder if I just need to run out as much fuel as possible, which could be quite difficult to determine, since my fuel gauge does not work, and I don't know how far/long I can go on a complete full tank.

All the gauges read fine on my display when this happens. Engine temp is right below 160. Volts is at 13. Oil pressure reports no problem. I'm completely baffled by this, and so far....none of the suggestions anyone has presented seems to have resolved this.

The only thing I haven't done is any carburetor adjustments or cleaning. Is there anything that stands out in my description that maybe I'm missing? Like I said, the most characteristic thing that happens is that I can start the engine, it idles between 500-600 rpm, and seems like it is always about to stall, and if I throttle the engine, it sounds like the engine is sucking in as much air as in can get, as if it is starving for air.

I wondered if maybe there is a 'warm idle', and it is set too low.

Any ideas? I'm not a mechanic, and haven't tinkered with engines for at least 20+ years now. This is driving me crazy, and (of course) putting a damper on my wakeboarding fun, having to limp back to the dock and end my trips earlier than I desire.

Please help in any way you can.....Maybe I need to find another mechanic?

Brian
Riding Melton Hill, Ft Loudon, Norris lake as the 48 yr old wakeboarder on the water! Smile

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PostPosted: May 26, 2014 8:52 pm    Post subject: Reply with quote

I agree with another mechanic. I had a problem with my old Ski Nautique and they had to rebuild the carb and everything was fine after that. The first shop told me nothing was wrong but once I found someone that was familiar with the old Holly carb I had they had it fixed in no time.
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pet575
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PostPosted: May 28, 2014 7:57 am    Post subject: Reply with quote

I have a 350 MAG MPI in my boat as well. You don't have a carb. MPI stands for multiport injection.

There are so many things that can go wrong it is very difficult to diagnose your problem (especially over the interwebs). I'd say the first/cheapest places to look are at your fuel and at your fuel pump.

Have you replaced the fuel filter/fuel-water separator? I think I'd remove that first and dump the contents of it into a clear glass container. Let it sit for an hour or two. If there is water in the fuel, it will separate out and you'll be able to see it.

If that doesn't get you an answer then your fuel is probably OK as far as water goes. I'd look at whether the fuel pump is functioning properly next.

Honestly, though, if it were me I'd go to a mechanic if they fuel doesn't have water in it.

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DJBusyB
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PostPosted: May 28, 2014 6:52 pm    Post subject: Reply with quote

Thanks...fuel filter and pump were on my target to check this week. My mechanic could not replicate the conditions and offered to ride around the lake with me until it exhibited the issue....at their standard $95/hr rate.

Brian

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PostPosted: May 29, 2014 4:31 pm    Post subject: Reply with quote

I agree that it could be water in the fuel.

Does your mechanic have a fuel injection fault code reader??
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DJBusyB
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PostPosted: May 30, 2014 8:38 am    Post subject: Reply with quote

Wheeler, I suspect not. When I took it in, I asked them to check this. Hopefully I will have my fuel filter replaced this weekend.
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PostPosted: May 30, 2014 11:32 am    Post subject: Reply with quote

Let me get this... you pay him$95 an hour to ride around the lake.. Man that is a great deal for him. I wish I were paid to ride around in a boat.
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DRAGON88
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PostPosted: Jun 01, 2014 11:39 am    Post subject: Reply with quote

Given that it only happens after components in the engine bay get heat soaked, I'd put my money on the fuel pump relay, it should be really cheap to just buy and replace.

Our Sport Nautique went through a phase where it would run fine but once up to temp it would sometimes bog down out of the hole or die all together. We swapped out the relay with a new one from Nappa (should be a easy part to hunt down) and the problem never came back.

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PostPosted: Jun 02, 2014 6:37 am    Post subject: Reply with quote

A bad ignition coil would also do the same thing.
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PostPosted: Jun 03, 2014 9:54 am    Post subject: Reply with quote

Initially I'd say bad fuel (dirty or wet), seen this many times... Remove, inspect and clean the fuel pickup in the tank. inspect the tank internally, is it clean or or there junk in there? Hook a fuel pressure gauge up and look for solid unwavering pressure. Seafoam, changing filters etc is not a guaranteed fix... if the fuel is bad it needs to be dumped.

Fuel pump relay should as Dragon88 says, be inspected, but you can also normally swap it with another on the motor as they are generally the same. Try this. Checking fuel pressure will also help point fingers in this direction.

If all this fails, hook up a test tank and run the boat with that.

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