Cobalt 200 Engine running rough

[Bcarl]

I have a 2004 Cobalt 200 with a Volvo penta 5.0 GXI-D and the engine is running really rough. (Engine rebuilt 60 hrs ago) Rpm’s will jump 1000-2000 with no throttle given to it. Acts like it’s starving for fuel but putting a lot of black discharge out in outflow water. It’s not oil but like unburned gas. Here is what I’ve done.

1. Replaced all plugs, distributor, and coil pack.
2. Cleaned out fuel tank
3. Changed fuel filter
4.Replaced map sensor
5. Ohm all injectors, all are good.
6. Fuel pressure is within range (gauge doesn’t hold steady, jumps a lot but in range)

What I haven’t done
1. Compression test every cylinder
2. Replaced throttle body sensor
3. Replace injectors.
4. Replace anti siphon valve.


Any help you guys can give would be greatly appreciated. We don’t have a lot of good boat mechanics where I live so trying to figure it out before I take it 1.5 hrs away.

[jhnmdahl]

Leaky fuel injector? Hard to diagnose without being there and fiddling with it, but that would be high on my list of things to investigate.

[Bcarl]

How would you go about finding a leaky fuel injector?