2007 Merc I/O Seems In Limp Mode

[Gsex10]

I have a 18' 2007 Crownline with a 4.3 Mercruiser I/O and only 120 hours. Never any issue. I left the boat tied to pier in River for one week as I was returning the following weekend. I have never done this. Last Saturday we headed out in the boat. backed out and I always Idle for a bit before starting out. The boat will only get up to 2200 RPM. It's like it is in a Limp mode but Marina mechanic's where I purchased the boat say there is no limp mode on I/O's, only OB. Everything they mentioned as something to look at I've done including new Lower Unit oil and New Prop. old oil perfect, no shavings. Boat runs absolutely smooth and all gauges read as they should. I can Rev motor up fully in Neutral and Rev to 4000-5000 in Reverse If I wanted to. I've got the best running boat that I can't use..... Any Ideas??

 

[Bt Doctur]

Are you actually going that slow or are you up on plane seeing that reading

 

[Gsex10]

I do not get to plane, Just stay up when in forward maxing out at 2200 RPM yet running smooth......

 

[achris]

MPI or carbed?

 

[Gsex10]

Carburated

 

[alldodge]

Which carb does it have, TKS, 2bbl, 4bbl ?
Engine serial numbers work pretty well

 

[Fun Times]

Depending on design, Maybe you have clogged up fuel tank vent tube/line/fitting from leaving the boat in the water for the week. Some fuel tank vents are now incorporated into the fuel fill cap so it's less of an issue but if the fuel vent fitting is protruding out the side of the boat then it could become clogged with debris.

To test this theory, all you have to do is open the fuel tank cap to let it breath better under load.

Does the engine sound different to you around 2200 RPM?

 

[Gsex10]

At 2200 RPM's it sounds as it normally would just prior to reaching plane

 

[captkevin]

How clean is the bottom of the boat after sitting for a week? Any growth on the bottom or prop could give you a similar problem.

 

[Gsex10]

2bbl carb. Boat has been cleaned. Has an alarm sounding now that begins at startup and have now run it out of water with Ears on and it will get above 2200 RPM's out of water But not in water under load. No impeller issues as steady water flow and T-stat (New) spot on at 180* when running in water.....

 

[Bt Doctur]

T-stat (New) spot on at 180* when running in water.....
A 160 stat should not get that hot??? blown head gasket maybe?

 

[alldodge]

I'm thinking the knock sensor or module. Look on the side of the block near the motor mount for the sensor. Can be part of the block drain when a Y fitting is used

 

[Gsex10]

So I just wanted to conclude the repair for this issue for anyone who was interested.......I stated that it was running smooth at 180* and when I seen the response by Bt Doctur and Stat temp questioned by a few others I learned that the t-stat for this engine is only a 140* T-stat so at 180* I was running warm, yet steady. The issue with the boat not getting above 2200 RPM under load turned out to be a cracked plug so a Tune-up of new Plugs, Wires, Cap and Rotor was completed at the Marina where I purchased the boat new. I found it odd though when told that the wrong plugs were in the Boat as everything in that engine is original from 2007 as the Boat only has 120 hours on it and nothing has been changed other than the regular fluids every year....... There truly is no system on the 4.3 L I/O that will send it into "Limp Mode".......The higher temp has been addressed by flushing out the manifolds from when I hit some sand causing the original T-stat replacement as it was stuck open.......All is good, Thanks for the suggestions!

 

[achris]

Cracked plug, who picked that one? Nice to hear it's fixed. And thanks for the closure.

Chris.....