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Volvo Penta 5.7 loses power under load

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tortguy

New member
I am new to boating and purchased a 2006 Four Winns that ran well for several months. It then overheated and a stuck thermostat was identified as the cause. It was replaced, as was the starter. Since then. the engine starts easily and revs well in neutral. However, when underway, the engine struggles above 2,000 or so RPM, such that I have to back off to keep from stalling. I am in Thailand. Replaced spark plugs, coil, fuel pump, to no avail. Checked the carburetor??? as well. Boat does not have a plug for computer analysis of engine performance.
 
Check your fuel/water separator and all fuel filters for contamination Are you runnning off the bottom half of fuel tank? You said you checked carb. what was exactly done to it? Removed,disassembled,cleaned throughly,soaked overnight,all passages blown through with water followed with dry compressed air,reassembled and reinstalled?
 
Is marine fuel there "blessed" with the addition of ethanol???
During the diagnosis/repair process, was the compression in every cylinder checked on engine?

Also DOUBLE check that the wires on the distributor go to the correct spark plug.
On SBC based engines, it is VERY easy to inadvertently swap plug wires at the block between adjacent cylinders... especially if you pull all the plugs out at once and then replace them.

When the plugs were replaced was the gap on the new plugs set to the specified range?
 
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Are you runnning off the bottom half of fuel tank?

I've seen this before, and don't understand it. Isn't the boat always running off the bottom half due to location of the pick-up ... :confused:
 
I was thinking along the lines of contaminated fuel, fuel pickup is in the very bottom of tank.You said engine overheated,has a compression test been done? Read Post#3 again
 
johnnygjr said:
I was thinking along the lines of contaminated fuel, fuel pickup is in the very bottom of tank.You said engine overheated,has a compression test been done? Read Post#3 again
Click to expand...
Since I have been operating the boat with minimal fuel in the tank, is there something else you recommend? Is there a filter in the tank? If so, how do you clean it?
 
Curmudgeon said:
Are you runnning off the bottom half of fuel tank?I've seen this before, and don't understand it.
Isn't the boat always running off the bottom half due to location of the pick-up ... :confused:
Click to expand...
Yes, it certainly is!

tortguy said:
Since I have been operating the boat with minimal fuel in the tank, is there something else you recommend?
Is there a filter in the tank? If so, how do you clean it?
Click to expand...

There is NO filter in the fuel tank.
However, most pick-up tubes are "screened" at the very bottom of the tube.
The pick-up tube can be removed so that the screen can be cleaned and/or replaced.



.
 
RicardoMarine said:
Yes, it certainly is!



There is NO filter in the fuel tank.
However, most pick-up tubes are "screened" at the very bottom of the tube.
The pick-up tube can be removed so that the screen can be cleaned and/or replaced. hre ttps://shop.aol.com/


I will clean the screen. Meanwhile, the Thai mechanic is coming out this weekend for further evaluation. I read somewhere once about a generator providing insufficient current and that being problematic for continued engine power. Is that possible? I thought a generator's sole function was to replentish battery power.
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..........................

tortguy said:
RicardoMarine said:
There is NO filter in the fuel tank.
However, most pick-up tubes are "screened" at the very bottom of the tube.
The pick-up tube can be removed so that the screen can be cleaned and/or replaced.
Click to expand...
I will clean the screen. Meanwhile, the Thai mechanic is coming out this weekend for further evaluation. I read somewhere once about a generator providing insufficient current and that being problematic for continued engine power. Is that possible?
Check the battery voltage after having been at rest for 6 hours or so.
At rest, you should see 12.4 volts.

While charging, you should see about 13.5 volts.

I thought a generator's (alternator??) sole function was to replentish battery power.
That is true.
An Alternator will not only replenish the battery's current loss, it will also keep up with current demands that do not exceed the alternator's charge rate.
Click to expand...
 
It wasn't easy, but a mechanic finally identified the cause of my boat engine bogging down under load. The engine had overheated six months ago due to a faulty thermostat. It was repaired. However, the overheating caused an exhaust manifold gasket to fail, creating a small water leak. This wasn't identified at the time. A prior mechanic had disconnected a sensor attached to the exhaust manifold; the sensor causes an audible ringing sound with overheating. The newest mechanic reattached the sensor; he ran the engine at high rpms and the alarm sounded, as the engine bogged down. The sensor is designed, with overheating, to automatically bog the engine down at high RPM's with overheating to avoid engine damage. So the newest mechanic changed out the leaking gasket and voila, problem fixed. Thanks for your various responses.
 
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