Mercrusier 350 MAG MPI - RPM issue under a load

[alldodge]

Is this a Bravo 1, 2 or 3 drive?

 

[wbas1]

Is this a Bravo 1, 2 or 3 drive?

Bravo 3 I am being told. It is also says that on the original paper work I have.

 

[alldodge]

ok, then change up
A 4x4 prop set of 18 = a 3x3 prop set of 20
So if you had 3x3 20Pitch you have about the same with 4x4 18Pitch

Go with a 3x3 18P

 

[Rick Stephens]

This seems all wrong. An 18 pitch is not going to be incredibly far off that you cannot get over 3400 RPM - no way. Are we sure the drive gearing is right for this boat and motor. You would need to drop down to a 12 or 11 pitch to get RPMs in proper range and that makes no sense at all.

 

[wbas1]

This seems all wrong. An 18 pitch is not going to be incredibly far off that you cannot get over 3400 RPM - no way. Are we sure the drive gearing is right for this boat and motor. You would need to drop down to a 12 or 11 pitch to get RPMs in proper range and that makes no sense at all.

Originally I was able to get to at least 4K by pulling the map sensor to give it more fuel. The mechanic said nothing is wrong with the motor. He had also mentioned the props. Nothing is really making sense with this boat.

 

[wbas1]

ok, then change up
A 4x4 prop set of 18 = a 3x3 prop set of 20
So if you had 3x3 20Pitch you have about the same with 4x4 18Pitch

Go with a 3x3 18P

So the 4 x 3 is no good correct?

 

[alldodge]

So the 4 x 3 is no good correct?

The more blades = more pitch
If you go from 3x3 to 4x3 need to drop more pitch

 

[wbas1]

Your original motor was most likely a 6.2 (and yes the block will be a 5.7 block)

The 6.2 ECM will dump more fuel

How can I tell if the original motor was a 6.2L? I still have the old block.

 

[Scott Danforth]

How can I tell if the original motor was a 6.2L? I still have the old block.

Measure the stroke. A stock stroke will be 3.48". A 6.2 liter will have a 3.75" stroke

Rocker arm ratio will also be 1.6:1 vs 1.5:1

 

[wbas1]

Measure the stroke. A stock stroke will be 3.48". A 6.2 liter will have a 3.75" stroke

Rocker arm ratio will also be 1.6:1 vs 1.5:1

I measured the stroke and it is 3 1/2” which is probably 3.48

 

[wbas1]

Update: I went back to the prop dealer and they are saying that with these props and motor the boat should jump out of the water. He also mentioned something else is going on with the motor that I am 1k RPMs off. I can only make about 3600 when I should at least be 4600. Well back to the drawing board.

 

[alldodge]

Would there happen to be a dyno shop nearby?

 

[wbas1]

Would there happen to be a dyno shop nearby?

I would need to take the motor out correct?

 

[wbas1]

Question: Can any of these sensors limit power on my motor?
1: NOC Sensor
2: Gear Indicator
I reached out to the Mechanic that looked at the motor last week and he pretty much told me there is nothing wrong with the motor and he would not even know where to look next. He just did not want to be bothered.

 

[alldodge]

I would need to take the motor out correct?

Yes, so it can be put on a stand and connected to the dyno

Question: Can any of these sensors limit power on my motor?
1: NOC Sensor
2: Gear Indicator

If ECM things the motor is not in-gear it will limit RPM. That said, if this did happen there would be an alarm. So if you get beeps when key is turn to RUN then this would not be the issue

Don't recognize NOC

I reached out to the Mechanic that looked at the motor last week and he pretty much told me there is nothing wrong with the motor and he would not even know where to look next. He just did not want to be bothered.

I haven't put my hands on it and I don't know where to go next my self. I'm here until we figure it out or you give up

 

[wbas1]

Yes, so it can be put on a stand and connected to the dyno



If ECM things the motor is not in-gear it will limit RPM. That said, if this did happen there would be an alarm. So if you get beeps when key is turn to RUN then this would not be the issue

Don't recognize NOC


I haven't put my hands on it and I don't know where to go next my self. I'm here until we figure it out or you give up

I meant to say Knock Sensor. As you can see this is just beating me up.

 

[wbas1]

Yes, so it can be put on a stand and connected to the dyno



If ECM things the motor is not in-gear it will limit RPM. That said, if this did happen there would be an alarm. So if you get beeps when key is turn to RUN then this would not be the issue

Don't recognize NOC


I haven't put my hands on it and I don't know where to go next my self. I'm here until we figure it out or you give up

I really have to say thank you for all your help. I am not giving up yet. I have a call out to the original owner to see if he can shed some light.

 

[alldodge]

The knock sensor will reduce power, but would also throw a code

 

[Rick Stephens]

I looked for it but didn't find. Did this motor get run on the Diacom software?

 

[wbas1]

I looked for it but didn't find. Did this motor get run on the Diacom software?

Yes the mechanic that came down had the software on the laptop and we took the boat for a ride. He did not see anything abnormal. He only gave me 2 screenshots.