VolvoPenta power problems at high revs under load

[RebelCobalt]

I oringinally posted this problem in the prop section, but I'm beginning to think it's an engine issue, not something slipping between the engine and the prop. I have a 1998 Cobalt 220 with a 5.0Gi VolvoPenta throttle-body fuel injection engine and a VP duoprop outdrive.

To summarize, the engine turns on fine, idles fine, and revs fine in neutral. It goes in and out of gear fine, and moves forwards and backwards at idle (600 rpm) ok. When you give it some throttle, it accelerates ok (if a little sluggishly compared to normal), but tops out at about 15 mph and 2,500 rpm. If you give it some more gas, the engine gets louder, but the revs don't increase, and there's no additional thrust. It's almost like it's run out of power. If you keep pushing the throttle down, it eventually chokes, so it seems like it's getting enough fuel (ie I don't think it's the fuel pumps - the high pressure pump is only 2 years old).

The spark plugs weren't in bad shape, and all looked consistent (no carbon deposits), although some of them seemed hotter than others. We changed the fuel filter and spark plugs anyway, since they were cheap, and hadn't been changed in a couple of years anyway. But it didn't do anything.

We checked the props, coupler to the engine etc, and couldn't see anything wrong. So I don't think it's an issue of getting power to the outdrive. It's like a manual car going up hill in 4th - just doesn't seem to have the oomph it needs anymore. And it's happened all of a sudden. It was fine over Memorial weekend, but when the wife and I took it out last weekend, it started doing this.

Any ideas of other things to check? The air intake doesn't seem clogged. We're going to check the exhaust valve flaps tomorrow. I'm wondering if they got too hot, melted, and are blocking the exhaust gas (their flapping used to be a lot louder than it is now)? Do you think that would give us the symptoms we're experiencing? Any other ideas? This one is really puzzling...

 

[Bondo]

Re: VolvoPenta power problems at high revs under load

Ayuh,.... It Sounds like it's goin' Lean, 'n starvin' for fuel,...

 

[RebelCobalt]

Re: VolvoPenta power problems at high revs under load

So check the fuel pressure coming in and/or replace the fuel pumps? Is there something else that could be causing the problem and worth checking beforehand?

 

[Jason89sunbird]

Re: VolvoPenta power problems at high revs under load

Another place to look at is injectors. You said a few of the old plugs looked hotter, if 4 of them where hotter then one of the injectors is bad. You can have someone drive the boat while you watch them spray and they aren't spraying the same replace the one that looks bad or both. If one clogged up from lack of use and gummy fuel the other isn't far behind.

 

[Don S]

Re: VolvoPenta power problems at high revs under load

You might want to get the engine hooked up to a diagnostic computer and see if it's being put into SLOW mode for some reason.

Here is from the service manual. Note the 2500 rpm where this happens.

S.L.O.W.[SUP]TM[/SUP]

The EFI system includes a protective feature called
Speed Limiting Operational Warning (S.L.O.W.). This
system prevents engine damage should oil pressure be
lost or engine coolant temperature become excessive.

The ECT sensor has a two-fold function; it supplies water
temperature data to the ECM in order to control spark
and fuel, and also triggers the S.L.O.W. system should
temperature reach or exceed 200?. A separate oil pressure
switch can also trigger the S.L.O. W. system should
oil pressure drop to or below 3-4 PSI.

Engine operation while in S.L.O.W. is distinctive. If the
system is activated at any speed above 2500 RPM, one
bank of injectors is immediately shut off and spark timing
is fixed at 8?. Boat speed will drop until RPM falls
below 2500. The engine will continue to operate on one
half the injectors at 8? unless RPM drops to 1200. At
1200 RPM, normal injector operation and spark timing
is restored (re-set point). The boat can now be operated
up to 2500 RPM in a normal manner, but if 2500 RPM is
exceeded and the cause of S.L.O.W. activation is still
present, one bank of injectors will again be shut off and
timing fixed at 8?.

S.L.O.W. will continue to perform in this manner until the
cause is eliminated. Should the cause be self-corrected
(i.e. weeds come off water screen, or oil re-covers
pickup), engine operation will return to normal when the
ECT senses water temperature at 180? or below, or oil
pressure exceeds 4 PSI.

 

[RebelCobalt]

Re: VolvoPenta power problems at high revs under load

So we figured out the problem this weekend - the exhaust flaps had come loose and got stuck further down the exhaust, impeding flow. We managed to cut them into two pieces in situ and pull them out through the exhaust, rather than remove the whole engine. Boat runs perfectly now, but I am flapless - I've heard there are tons of boats running fine without flaps, but is this true? I would have to replace the whole exhaust section where the flaps are (the holes that the pin sits in have become too big, which I think is why I lost the flaps in the first place), and this would require removing the engine, which I am reluctant to do...

 

[Jason89sunbird]

Re: VolvoPenta power problems at high revs under load

There is a service bulletin that tells you to remove the flaps. I believe they started not coming with the flaps sometime in 98-99. Now you know why lol

 

[HalfFish5087]

Re: VolvoPenta power problems at high revs under load

There is a service bulletin that tells you to remove the flaps. I believe they started not coming with the flaps sometime in 98-99. Now you know why lol

Jason is correct, it was '99 when they stopped adding the flaps and issued a bulletin saying there were not needed. I have seen the bulletin floating around somewhere here on iboats and I believe it was posted by Don S (volvo grand master).

Luckly, I caught mine before they fell, but like you they had worn large oblong holes in the y-pipe. I was rebuilding the transom so I already had my engine out at this time and went ahead and welded up the holes.