2001 Volvo Penta 3.0 Loses Power

Hello All,
I have a 2001 Smokercraft V186 Fish-n-ski with a Volvo Penta 3.0L engine. It is new to me (2 months). It ran decent the first several times I had it out, but one thing led to another, and stuff keeps happening. Bad stuff... Originally, it hesitated during full throttle. I would give it FT, and it would bog down and sputter, and eventually die. I would have to slowly give it throttle for it to take off. So, being the mechanic that I am, I ordered a rebuild kit for the carburetor. Only to find out that the carburetor is not original. Big shock, right. So, after getting the correct rebuild kit, rebuilding the carburetor, and testing it, it flat out ran like crap. During this test run, the engine overheated. Naturally, the impellar was toast. So, I ordered a sea water pump rebuild kit. Pretty easy. Once I removed all of the pieces of the old impellar, I took it to the boat ramp and backed it down in the water. I didn't take it off of the trailer, but I started it, and let it run for about 15 minutes. Temp was normal (150-160)the entire time, so I thought it was a done deal. The next day, we took it out and began enjoying the money pit. After about an hour of pulling a tube, it began to lose rpm's. It would get up to 4000, then start dropping. If I leave the throttle in a wide open state, the boat will slow to a crawl, and only idle. I pull the throttle up to neutral, then back to forward, but the rpm's will NOT increase at all. So, I turned the engine off, wait about 5 seconds, then start it back up. I put it in gear and the whole process starts over. WOT, 4000 rpm's, then back to idle. I've looked all over this silly boat for an ECM, PCM, whatever, but haven't been able to locate one. Any help would be greatly appreciated. I'm pretty sure I've included any information one might need to make an educated guess (SWAG), but if not, feel free to ask. And thank you, in advance.

 

New Carburetor

I did forget to mention that I bought a new OEM carburetor. The engine runs like a champ. I've also replaced the temperature sender, and switch, along with the oil pressure sender and switch.

 

If the engine is carbureted there will be no reason for an ECM (engine control module ....computer) If the engine had been fuel injected, then, yes, a control module is needed. You apparently have the problem conquered so good to go.

Judging from some of the descriptions of the engines behavior, My first guess is that the non OEM carb was too big. The previous owner may very well have been snookered into believing that a larger carburetor bore would let the engine deliver more power. Hogwash!! Even a very small increase in the size of the venturi section of the carb can affect the engine behavior drastically and not in a positive way.. So now you have an OEM carb whose details comply with the design of the engine and it works very well. Increasing the output of a piston engine is a matter of very complex sets of factors....camshafts thus valve timing, compression ratios, connecting rod length to stroke ratios, system volumetric efficiency and lots more that have to work in concert with one another.

Good for you, the correct air/fuel supply system which is the carburetor and its air filtering components works as the manufacturer said that it would.

Please excuse the mini rant. I have been in the racing engine business for a very long time and I am irritated by false claims by hustlers who make wild claims about carburetors, magic camshafts, ionic fuel converters, and other gimmicks that have no basis in fact.

Glad you got your boat running well........enjoy.

 

Do you happen to have an opinion on why it loses power, and goes into a limp-like-mode, or safe-mode?

 

It could be a faulty pickup coil or ignition coil too. However, before changing anything, make sure the timing and advance are working. If they are, take a timing light with you and check again when the engine won't rev up.
https://www.perfprotech.com/blog/articles/mercruiser-engine-timing

 

Okay. It's been a while since I posted this, but I thought I'd let anyone who wants to know what I found know what the problem was. On the upper right side of the engine there is a bracket that holds the throttle cable in place. That bracket has a clamp in it that holds the cable. That clamp came loose and would allow the throttle cable to slip back into the throttle cable "jacket". So, when the engine was at high rpm's, it would vibrate loose and the cable would slip. Thanks to all who responded.