1994 OMC Cobra 5.8 only 75% power

[Davek55]

Hey All
I bought a '94 Four Winns 22' cuddy this Spring and have had it on the water many times and it has been running great. This is when it all changed: We were pulling kids up on wakeboards all day but then when we attempted to pull my son up again we had no power. The change was very abrupt.
The engine idles and runs very smooth but only makes about 3700rpm and about 15mph less speed than usual.
I don't think the prop has spun because RPM is low.
We checked engine OBD1 codes and it seems we are getting code 11 = Systems Okay.
We disconnected the oil press switch to check limp mode but the limp mode causes surging at 3000rpm which is a very different symptom.
What am I missing....? Thx!

 

[Davek55]

Hey All
I bought a '94 Four Winns 22' cuddy this Spring and have had it on the water many times and it has been running great. This is when it all changed: We were pulling kids up on wakeboards all day but then when we attempted to pull my son up again we had no power. The change was very abrupt.
The engine idles and runs very smooth but only makes about 3700rpm and about 15mph less speed than usual.
I don't think the prop has spun because RPM is low.
We checked engine OBD1 codes and it seems we are getting code 11 = Systems Okay.
We disconnected the oil press switch to check limp mode but the limp mode causes surging at 3000rpm which is a very different symptom.
What am I missing....? Thx!

Also, we replaced the fuel filter. I ordered a fuel pressure gauge and will test it this weekend.
Previously, we misinterpreted the OBD1 flashes and swapped the TPS sensor and then the MAP sensor today.

 

[Lou C]

Consider checking the fuel tank vent and the anti siphon valve on the gas tank.

 

[Scott Danforth]

check engine compression
check fuel pressure
check quality of fuel
check fuel filter

 

[Davek55]

Resolved!
Found an exhaust flapper had fallen apart and was stuck in the bottom of the y pipe just before the bellows to the stern drive. I removed the rubber bellows flex hose and was unable to push the flapper back up towards the engine so I extracted it by breaking it apart into pieces and pulling it out towards the stern drive.
I will pull the stern drive apart and look for the pin when we get home from camping....but for now it is running great and we are back to doing watersports.
It seems there was a service bulletin recommending not using flappers. Hopefully I'm not mislead...but planning to run without them permanently.
Cheers
Dave

 

[Lou C]

That was a Volvo Penta service bulletin, and they advised removing them, but OMC did not. I have had the flappers on mine all this time (owned it 19 years) and the only time I had an issue was after a bad overheat, so I replaced both of them. I'm not sure that I agree with V/P, and I would replace the flappers, because with them I have never had a hydrolock on my boat, in all this time, using 2 different design exhaust systems (the original one piece Batwings and the later 2 piece style). Mercruiser has always used flappers, I'm not sure how V/P came to the conclusion that they are not needed. The parts are available and not expensive.

 

[Davek55]

That was a Volvo Penta service bulletin, and they advised removing them, but OMC did not. I have had the flappers on mine all this time (owned it 19 years) and the only time I had an issue was after a bad overheat, so I replaced both of them. I'm not sure that I agree with V/P, and I would replace the flappers, because with them I have never had a hydrolock on my boat, in all this time, using 2 different design exhaust systems (the original one piece Batwings and the later 2 piece style). Mercruiser has always used flappers, I'm not sure how V/P came to the conclusion that they are not needed. The parts are available and not expensive.

Thanks Lou....I guess as they say...an ounce of prevention is worth a pound of cure.
We will run the boat as is this week as I don't want to miss out on any fun on the lake.... but will replace them. The holes are ovaled out and will require bushings. At least if it ever happens again it will be easy to diagnose and fix.
Thanks again

 

[Lou C]

You’re welcome!