2005 Mercruiser 350 MAG MPI Engine Problems

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kclbrooklyn

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So a few weeks ago I was on my 2005 Chaparral Signature 240 equipped with a Mercruiser 350 MAG MPI with a Bravo Stern drive. I used the boat only about a dozen times during the season and was heading to have the boat winterized. The engine has about 100 hours on it. I was heading from Brooklyn, NY to Jersey, City cruising at about ~ 22 Knots against the current running the engine around 3400 RPM when I realized I had broken the rule about having enough fuel as I started my trip with what appeared to be a bit under a quarter tank of gas on my 70 gallon tank. While heading towards the Jersey City marina fuel station I realized I overshot the channel markers and promptly put the throttle into neutral, the boat lurched and then the engine cut off. I tried to start the engine a few times but it would cut off soon after starting. I had assumed I ran out of gas and was lucky to find a passing trawler that held me in place until a passing Coast Guard vessel towed me into the fuel dock. After filling up with gas, I started up the engine and sighed a breath of relief but then soon after my engine cut out again. I opened the engine compartment to find that the engine belt had slipped off the engine. I was a bit perplexed by this as this had never occurred and with some help I was able to get the belt back on. I started the engine again and it seemed to be OK but after about a minute it cut out again. An employee at the fuel dock suggested perhaps the issue was fuel related and recommended I add some Star Brite Star Tron Gasoline Additive. I did this waited about 15 minutes and when I started up the engine, still it run for about 45 seconds to a minute then it stalled. Another boat owner suggested there could be a problem with the fuel filter. So I went ahead and replaced the fuel filter and I noticed the old fuel filter was a bit dirty. This time when I started the engine it would run idle for an indefinite period of time but whenever I applied throttle above 1200 RPM then engine would shortly cut out. I had the boat towed to the mechanic who told me one of the fuel pumps was showing low pressure. He replaced both fuel pumps and although I was told my fuel pump pressure is OK, the engine keeps cutting out. He used a Rinda MerCruiser Scan Tool to check the engine but says its not reporting any faults. I was then told it could be the ignition coil and spark plugs so they too were replaced but the end result is that the engine appears to run fine on idle for an indefinite period of time but when throttle is applied for more than a minute or two the engine cuts off. The mechanic has a case open with Mercury but any suggestions out there? Anyone run into a similar situation?
 

newport dave

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

Kinda sounds like your mechanic is just guessing and replacing stuff and not really doing proper diagnostics. Anyone else is your area that you could take it to?
 

kclbrooklyn

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

Well now I have been told that all the problems were caused by a loose ECM wiring connection. Could this be a plausible explanation?
 

Bondo

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

Ayuh,....

Anything is Possible...
 

newport dave

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

I would believe it when I took the boat out and tested it.
 

MikDee

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

Check your fuel tank vent, and make sure your fuel pressure is at the recommended specs. These MPFI engines require high fuel pressure, and are sensitive to anything less.
 

dsteele1

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

I'd lay odds that it's your IAC valve malfunctioning. Stands for Idle Air Control and it basically is an electronically controlled air inlet valve used to control the air intake at very low RPM's (idle) when the throttle body valve is closed. If it sticks closed your engine will starve for air and shut down quickly. About a $90 part and 15 minutes to change it out.

P1010321IACValve.jpg
 

jmtrice

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

Hi There;

Not sure if anyone is still reading this thread, but I was just out on my boat for an extended period of time, and lets just say the trip didn't end well, I had to cross the Strait of Juan De Fuca in 25 knot winds on my 8hp kicker!

I crossed one way and the engine ran well, but when entering the harbor, pulled back on the throttle and the engine sputtered and died, it started back up and we went to customs and checked in, but after that the engine wold not run, it would start and run for 1-5 seconds and then die. It seemed like a fuel supply problem. Ended up getting a master tech for Merc to test it and the problem was slowly fixed? Even he was confused. He couldnt find any faults (one thing he thought was wierd was when he disconected the Oil pressure sensor, his computer did not read zero, it read a standard 50.8 (i think that was the number). The fuel injector preasure just kpt falling off, adn he would drain some off, fiddle with things, and finally, it was just fixed?? I have just replaced both fuel filters one week ago and have brand new gas with Startron in it. I know the supply fuel pump is working, but I do not know if the "cool fuel" pump is. I can hear the supply pump every time I key the engine, before starting.

This issue with an IAC valve sounds like a plausible explanation. I am pretty mechanically inclined, but dont know anything about replacing them. Is it pretty easy? Cna you pull them off and inspect easily?

I am looking at your posted picture and it looks like it might just be an alan key to remove?

Thanks for any help.

John T
 

akbushman

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

I had a 2003 350 mag mpi put in my 32ft aluminum boat. The motor from what I am told is to be plumbed into raw water. The place I had the motor installed at said it would be no problem plumbing into my keel cooler. Have got the motor in and everything hooked up but either the motor pushes my antifreeze out my expansion tank or they tried putting a solid cap on my expansion tank and it seems to run that way but slowly over heats. The guys that installed the motor say they havent seen many motors that are plumbed like this one. If some one could get me the systems water routing diagram and how to plumb it in to a keel cooler that would be great..... Thanks
 

ENSIGN

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

Pump some gas directly out of the tank there may be a water/gas mix.
 

Bondo

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Re: 2005 Mercruiser 350 MAG MPI Engine Problems

I had a 2003 350 mag mpi put in my 32ft aluminum boat. The motor from what I am told is to be plumbed into raw water. The place I had the motor installed at said it would be no problem plumbing into my keel cooler. Have got the motor in and everything hooked up but either the motor pushes my antifreeze out my expansion tank or they tried putting a solid cap on my expansion tank and it seems to run that way but slowly over heats. The guys that installed the motor say they havent seen many motors that are plumbed like this one. If some one could get me the systems water routing diagram and how to plumb it in to a keel cooler that would be great..... Thanks

Ayuh,... You can expect few to No answers, because you Hi-jacked this 2 Year Old thread...
Start a thread of your Own, about Your problem to get some Great answers....
 
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