Volvo Penta 8.1 - Tops out at 3000rpm

3_Little_Birds

First time boat owner and I'm out of troubleshooting engine issues on my 2005 Rinker 360 with twin Volvo Penta 8.1s (375hp). First symptom in May was the boat would sometimes plane, sometimes not. Then the power steering fluid reservoir went dry. I filled the power steering and replaced the fuel filters thinking this was a fuel delivery problem. Power steering came back, still can't get up to speed. A friend of mine pressure tested the fuel lines and one engine had zero psi on the low pressure pump and the other had 35-38psi on the high pressure pump. We replaced both engine fuel pumps. Still no change. At some point, my power steering fluid emptied because I lost p/s and the reservoir was dry again. Filled back up two weeks ago and no sign of leaking. I hauled the boat out and pressure washed the very dirty bottom (it had been a year since last pressure wash). Still no change on engine performance. Any ideas? Is there a computer mode to "govern" the engines if there is a problem. Is there a "sync" function at play here where one engine is the master and the other slaves off of it. I say that because my Sync gauge at the helm has always been pegged towards Starboard since I bought the boat in Dec 20. I've research what that means and I still don't have a clear answer. Of course, that may have nothing to do with my engines not performing under load. Any advice is appreciated, but the advice that solves this enduring problem is mostly appreciated : )

3_Little_Birds

I forgot to add that in neutral both engines rev up normally to 4500-5000rpm.

Aqua_Aura

I only have a single 8.1 so I can't help with the sync. Are both of the engines not going past 3000 RPM? I would replace plugs and then ohm check your wires to begin and it would seem you solved some fuel delivery questions with the new pumps. There is a pressure regulator on the fuel rail on the engine that could cause issues, after replacement you said no change but was it no change in performance or still 0 psi on the low pressure? If your old pump started to lose paint it can clog all sorts of stuff in the fuel system. The original pumps and replacement fuel pumps are painted inside unless you bought new ones from man cave mechanic. 

You may need to consider sending your injectors out to be cleaned if the wires and plugs are good. You shouldn't have a cap and rotor to worry about. These Volvo engines seem to be bulletproof and easy to maintain from my experience. 

Aqua_Aura

3_Little_Birds said:

I forgot to add that in neutral both engines rev up normally to 4500-5000rpm.

That's normal with no load that a bad running engine will rev up. 

YYZRC

Sounds like your power steering cooler has rotted out. Mr Cool makes good aftermarket replacements. Easy to change. It’s located at the back of the engine in the middle. 

Have you replaced plugs, cap and rotor, wires?

Aqua_Aura

Shouldn't have cap and rotor on that engine. Not sure what year they went to coil packs but it should be on that year like mine. 

skennelly

Had a similar problem recently.  New wires and plugs did wonders.  One of my wires were nicked I bet causing a cylinder to miss

reneechris14

8psi on low pressure side and 43psi high pressure is normal. I would agree with others on plugs and this would verify fuel and spark. The cpu will not limit you to 3000rpm but will limit if there is a problem(code set). If one motor is low on power the other will not rev up to compensate. If an injector is bad the plug will be dry.

3_Little_Birds

Thanks for the suggestions. YYZRC - Will check the p/s cooler. Aqua_Aura - fuel pump pressure readings changed to acceptable limits after fuel pump replacement (low: 15 psi, High: 40-45), although high pressure readings were jumping around on the gauge. Engine performance did not change. Yes, no cap and rotor on this engine. Reneechris14 - appreciate the info. Not sure if there's a problem code set, but perhaps one engine is staying at the same rpm level as the problem engine. Ordered new spark plug kits to replace plugs/wires. I will update my progress. Thanks everybody!

3_Little_Birds

Update: Spark plug replacement worked! I thought I ordered kits with the plug wires, but only plugs. That solved the power problem. Twp test runs and the engines got up to 4300rpm and 38mph under load. Beautiful sound. Now, on to the power steering problem. The p/s pump on the starboard engine sounds bad so I'm ordering a replacement. I'm told the port engine p/s is not in use at all. Can I swap the p/s pump on the port engine with the starboard engine?

aero3113

You can, but I would put the new pump on the starboard side.

YYZRC

Someone on here removed the port pump completely and ran a shorter belt. Brilliant in my opinion. 

aero3113

YYZRC said:

Someone on here removed the port pump completely and ran a shorter belt. Brilliant in my opinion. 

I’m sure it’s very minimal, but do you think the port engine would run at a higher RPM since there’s less load?

YYZRC

I asked that question and consensus was it would be a minimal difference.

When you balance the boat with trim tabs I assume one motor runs a bit harder to compensate for the drag?

Michael T

@3_Little_Birds.....good news but I'm still not happy that you are running only 4300 RPM at WOT. Your RPMs at WOT are out of specification. Those engines are being lugged more than I would allow on mine.

Aqua_Aura

4600 is max so it may just be gauge inaccuracies. 

3_Little_Birds

Appreciate the updates! I am getting a new pump for the starboard. I like the idea of a shorter belt on the port engine and bypassing the p/s pump. As for max rpms on WOT, I don't trust my gauges so I'm not as concerned about the max rpm readings. I'll keep my eye on it though.