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Old 07-13-2009, 12:56 PM
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Andyg Andyg is offline
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LY6 Engine Won't Rev Past 3000 RPMs

I was out on the 4th of July with my 2008 PS197 with the LY6. As soon as I took off from the boat launch I new something wasn't right. The engine would not rev over 3000 rpms in gear or in neutral. No engine codes came up that set off the check engine alarm. The engine seemed to run fine except for not going over 3000 RPMs. I checked the fuel pressure and it was over 60PSI. I then disconnected the battery and tried to reset the computer. That didn't work either.

On Monday I took the boat to the dealer closest to where I was on vacation, 2 hour drive one way. When they fired up the boat in the shop it ran fine, saw it with my own eyes in the shop. The technician said there were no engines codes either. The weather didn't permit me to take the boat out the rest of my vacation so I didn't get a chance to see if the problem was gone.

I took the boat out again yesterday and it ran fine for several hours. Then after floating for a while I started the engine back up and the problem was back. Again there were no engine codes that triggered a check engine alarm.

Does anyone have any ideas what could be causing this since no engine codes are present? I am taking it to my local dealer this Friday, but I am concerned that they won't see the problem either. The boat acts like it is in "limp" mode. But my understanding is that for the boat to go into "limp" mode an engine code must be present. The only thing that I can think of is that I got some bad gas and the knock sensor is triggering the boat to cut the RPMs. The frst time it happened was immediately after I filled up with gas. I am now down to a 1/4 tank so if I fill it up with new gas I would think that should eliminate gas as the culprit. Any ideas?

Thanks

Andyg
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Old 07-13-2009, 04:48 PM
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panamawake panamawake is offline
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does your boat have perfect pass? the servo might be loose, not an expert but just throwing that out there, did you try accelerating it manually from the motor?
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Old 07-13-2009, 05:16 PM
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f16driver f16driver is offline
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Andyg,
What does the motor do when it gets above 3000 rpm....does it pop or backfire or stall or how would you describe it?

F16Driver
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Old 07-13-2009, 05:22 PM
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Quote:
Originally Posted by panamawake View Post
does your boat have perfect pass? the servo might be loose, not an expert but just throwing that out there, did you try accelerating it manually from the motor?
It is a drive by wire system so the typical servo that controls the thottle cable is not there. Also because it is drive by wire I don't think I can manually accelarate the engine. I will take a look though.
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Old 07-13-2009, 05:23 PM
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Quote:
Originally Posted by f16driver View Post
Andyg,
What does the motor do when it gets above 3000 rpm....does it pop or backfire or stall or how would you describe it?

F16Driver

If the motor goes above 3000 rpms there are no problems at all, it runs totally normal. In fact when the problem occurs the engine seems to run fine all the way up to 3000 rpms, but just won't go any higher.
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Old 07-13-2009, 06:37 PM
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panamawake panamawake is offline
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it could be low oil pressure or high transmission oil temperature if your boat is kicking into power reduction mode which limits your speed intended to allow you to get to shore fix the issue. I would recheck your temperatures and oil pressures.
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Old 07-13-2009, 06:43 PM
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Originally Posted by panamawake View Post
it could be low oil pressure or high transmission oil temperature if your boat is kicking into power reduction mode which limits your speed intended to allow you to get to shore fix the issue. I would recheck your temperatures and oil pressures.
I know for a fact on this setup if there is a high transmission oil temp it will throw a code. On my 2007 with the LY6 I had that exact problem. All fluids checked at the proper level. Oil pressure and engine temp were in normal operating ranges.
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Old 07-13-2009, 07:00 PM
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f16driver f16driver is offline
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Quote:
Originally Posted by Andyg View Post
If the motor goes above 3000 rpms there are no problems at all, it runs totally normal. In fact when the problem occurs the engine seems to run fine all the way up to 3000 rpms, but just won't go any higher.
Are you saying that sometimes the motor just runs fine right up to and above 3000 rpm with no problems and other times it just wont go above 3000rpm? Describe what it does when it wont go above 3000 and you push the throtle further forward?
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Old 07-13-2009, 09:51 PM
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Quote:
Originally Posted by f16driver View Post
Are you saying that sometimes the motor just runs fine right up to and above 3000 rpm with no problems and other times it just wont go above 3000rpm? Describe what it does when it wont go above 3000 and you push the throtle further forward?
Exactly. If you give it full throttle out of the hole it will actually bounce off 3000 rpms and hop around just below 3000 rpms before settling in. It isn't back firing or making any funny noises up to 3000 rpms. It reminds me of when I miss a shift on my Harley and I am bouncing the engine off the rev limiter. If you give it about half throttle it will climb quickly up to 3000 rpms and just stop. Sometimes if you try and give it more throttle at that point it will also feel like it is hitting a rev limiter and the RPMs will bounce around a little. No matter how much throttle you give it though it won't go over 3000 RPMs.
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Old 07-14-2009, 07:39 AM
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f16driver f16driver is offline
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Andyg,
My 2003 Prostar 197 with LQ-9 engine at one time would not go above 3500-4000 rpm. Your description about hitting the rev limiter is similar to my experience. I realize that your engine and mine are different and that your problem could be caused for different reasons. The day my boat started running normally I had done 3 things and I can only guess which item solved the problem. One morning I replaced the fuel pump, the spark plugs and discovered 1 spark plug wire that was faulty. The wire cap was snug and secure on top of the spark plug. But when I was trying to remove the plug wire cap from the spark plug, the wire pulled out leaving the cap sitting on the spark plug. I repaired the wire cutting off the bad end and reinserting the plug wire cap, making it a tad shorter wire. A bad wire may not be noticeable at idle but could present itself at higher rpm. Your boat is basically new and I dont know if your fuel pump suffers from the same fuel pump issues that earlier MC's have, but on mine and alot of others the fuel pump has been a problem. If we ever let the tank get low the pump will suck in debris from the tank bottom and clog the pump. When I removed my pump assembly from fuel tank I found the actual pump inside the casing was not sitting properly secured in the assembly and was able to move around. It wasn't suppose to do that. Sometimes my boat would lose power in a hard turn, maybe it was the pump shifting to one side and fuel flow to the pump was disrupted, maybe...A new pump is really expensive from MC. And last, I replaced all my spark plugs because of a factory recall. I dont know which one item fixed my problem (because I fixed all 3 and then went for a test drive)but your description of your problem sounds similar to my problem. Btw...my boat was was 3 1/2 to 4 years old when this occurred but only had 30 hours on it. I'm betting in my case it was either the plug wire or the fuel pump, but could have been a spark plug. If you havent checked either of these items this might be a place to look. Can you borrow a working pump from a friend. My neighbors and I have a spare pump for swapping and diagnosing pump problems. It takes about 30 minutes to change a pump out on my boat. If you do purchase a new pump assembly from MC dont throw out the old one. Several guys on this forum have rebuilt their pumps using automobile pumps to replace the MC (carter) pump. All of this assumes your handy with tools and are willing to do the work yourself. Obviously working around fuel is not for amature mechanics.
Good luck and don't forget to share with us all what finally fixes your problem.

F16Driver
03 Prostar 197
LQ-9
Fredericksburg VA
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