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Premium Member
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Discussion Starter #1
Ok... Let's do a little diagnostic test. 07 Howard Sportdeck with a 600sci. Last weekend we took the boat out and when the boat was under load and going over 4500 rpm the engine cut out intermittently. An alarm also sounded giving a three beeps then repeated. One time it cut out when I was coming out of the hole moderately aggressive. I checked the temperature, oil pressure, drive fluid etc. all looked perfect. When starting the engine it seemed a little slower to fire than normal. After it started it idled smooth and ran fine until it was under load and then had the bad miss. Aaron from Absolute Speed and Marine is picking up the boat tomorrow to take it in and have a look. What do you think is wrong?

oil related?
temperature related?
drive related?
water pressure related?
electrical problem?
fuel supply problem?

The boat has been maintained well and has new plugs, impeller, all fluids changed etc recently. 50 hours on boat and motor.
 

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Maxwell Smartass
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353 Posts
Possibly running out of fuel misfire was my first idea, but at first i thought you said 600sc (older carbed model) not the new injected sci. I have heard of engine wiring harness problems on quite a few of the new merc engines causing sporadic problems when the boat is underway. That's about my only guess based on initial statement. I'm sure the guys at absolute will figure it out, i've heard nothing but good things about them.
 

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Nuclear Powered
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1,281 Posts
I'm betting on the fuel.

Water in tank.....
Fuel strainer/filter
Fuel pump
Loose wire to fuel pump (including the battery cables)


Does your battery gauge indicate a sudden loss of power when your engine looses power?

Good luck....
 

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It is what it is
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2,650 Posts
Under load only? Knock sensor going off from bad or low octane fuel, fuel delivery problem possibly. Could also be a loose wire that has a bad contact when the motor is vibrating. Like a loose ground wire on the block, loose positive on the starter or even a loose wire at your ignition or kill switch on your dash.

Gremlins on pcm motors can be hard to find. Be patient, it may take a few times to figure out.
 

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"BOUGHT NOT BUILT"
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8,077 Posts
merc had a problem with oil pressure senders , the motor has good oil pressuer but tells the ecm that it's low, puts it in gaurd mode, which is where you are now,

one scan will tell
 

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Ok... Let's do a little diagnostic test. 07 Howard Sportdeck with a 600sci. Last weekend we took the boat out and when the boat was under load and going over 4500 rpm the engine cut out intermittently. An alarm also sounded giving a three beeps then repeated. One time it cut out when I was coming out of the hole moderately aggressive. I checked the temperature, oil pressure, drive fluid etc. all looked perfect. When starting the engine it seemed a little slower to fire than normal. After it started it idled smooth and ran fine until it was under load and then had the bad miss. Aaron from Absolute Speed and Marine is picking up the boat tomorrow to take it in and have a look. What do you think is wrong?

oil related?
temperature related?
drive related?
water pressure related?
electrical problem?
fuel supply problem?

The boat has been maintained well and has new plugs, impeller, all fluids changed etc recently. 50 hours on boat and motor.
Had the same issue last year.... Water Pressure sensor was bad....
 
U

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Ok... Let's do a little diagnostic test. 07 Howard Sportdeck with a 600sci. Last weekend we took the boat out and when the boat was under load and going over 4500 rpm the engine cut out intermittently. An alarm also sounded giving a three beeps then repeated. One time it cut out when I was coming out of the hole moderately aggressive. I checked the temperature, oil pressure, drive fluid etc. all looked perfect. When starting the engine it seemed a little slower to fire than normal. After it started it idled smooth and ran fine until it was under load and then had the bad miss. Aaron from Absolute Speed and Marine is picking up the boat tomorrow to take it in and have a look. What do you think is wrong?

oil related?
temperature related?
drive related?
water pressure related?
electrical problem?
fuel supply problem?

The boat has been maintained well and has new plugs, impeller, all fluids changed etc recently. 50 hours on boat and motor.
Mine acted this way from a bad lanyard switch
 

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Premium Member
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729 Posts
Discussion Starter #13
Relaxalot:

I guess you have your answer to your fuel thread now.......

http://www.performanceboats.com//showthread.php?t=3297

Aaron is picking it up today and I will let you know the diagnosis. The fuel was bought at Terribles and was new. Since this fuel thread I have had no fuel related problems. I spoke with Dustin Whipple and he said that he thinks it probably is a water pressure issue. The temperature is cool both water and oil. I am curious what the diagnostic tool will indicate. Hopefully something minor.
 

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Premium Member
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Discussion Starter #14
Aaron called and said that the only thing he found so far was a sensor on the shift linkage was out of adjustment. He is taking it out for a lake test.
 

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We had a similiar problem 2 years ago. The boat would cut out at about 3000rpms. Sit down then kick back in. The guys that did the service forgot to plug one of the fuel pumps back in. Since there is 2 pumps it would run fine at normal speeds until you put the hammer down. Took a while to figure out since there were no sensors going off.
 

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Relax , Try taking the 90A fuse block [ little square box] off at the starter/battery cable connection, run the boat without it to see if the problem still persist.
I found the through bolt/nut on this fuse loosens and the drop in voltage causing the problem for the ECM. Snug up the bolt/nut and try it again.
Just another possibility.
 

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I vote Batteries..

I'll say that you're battery is not fully charged and you alternator can't keep up with the load of the engine computer... I had the same problem on my old boat with a 502MPI Mag, and when it would get around the same rpm it would choke and spit... changed 1 battery in the marina and it was golden... apparently the battery was good to start the boat, but couldn't keep up with the computer load... that's what they told me at least.. all I know is that it ran fine after the battery change, and the alternator was just fine (65amp)...
best of luck!!
 
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Aaron called and said that the only thing he found so far was a sensor on the shift linkage was out of adjustment. He is taking it out for a lake test.
Please keep us posted. I'm really curious to hear what the problem is.
 

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Premium Member
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Discussion Starter #19
Interesting thought about the battery charge. I did notice it having problems after I had run the stereo a long time. I have two interstates and one large stinger battery.

Well Aaron at Absolute came through for me. He took the boat out today with a fresh load of fuel(this is another potential issue). Of course the boat ran great. He checked it with the scan tool and he said that it had a sensor on the gearshift that needed adjustment that kicks up the rpms when it shifts into gear. He changed the small fuel filter that is immediately before the injectors. He said it looked perfect and the scan tool indicated no other problems. He said that he tried to duplicate the problem but, of course, the boat ran awsome. Could it have been a bad fuel load and when the ecu called for boost, the knock sensor kicked in and protected the engine? Well, I am going out on the water tomorrow and I will report if all is well. Crossing my fingers.....
 
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