I know Others have had issues like this. But I’m also having issues and haven’t got it figured out yet. . I would appreciate any help as I have just about exhausted my ideas on how to fix it. Boat runs excellent. You would not know there was a problem except for the black transom on the port engine.

This is what I have done.
ECM’s have been checked out and they are right on target.
new injectors from BUP. (He’s been trying to help me but still looking for ideas. He has been very helpful)
Most sensors Changed, map, air temp, TPS,
fuel regulator changed out. knock sensor
excellent compression all cylinders
new wires and new coil.

i haven’t changed the water temp sensor yet.
I had an ignition trigger go out and I changed it. I have really strong ignition spark too.

I’m at a loss. The transom is not just lightly sooting, it’s black. I’m not making any headway. About ready to take it to someone and let them figure it out. I would appreciate anyone’s help or advice. I’m in NE Okla if you know anyone capable and good that may be able to fix it.

thanks everyone😄

Have you checked fuel pressure?

Actually no. That’s next on my list. I don’t have tool but need to get one. Thank you.

So a dumb question for you. So why would low pressure cause too much fuel and sooting?

What octane fuel are you running?

X 2 on too high octane of fuel. If 87 or 89 is used check fuel psi. Could be high.

These should have been first two things to check/adjust.

Years ago tons of 500EFI soot threads. 2 high of octane was numero uno cause.

I’m running 91. But a bit of background. I’ve owned this boat for 17 years. The starboard engine is fine. Runs 91 as well. All new injectors on it too. Both motors are freshly rebuilt and freshened up. This has been a ongoing problem. I tried 89 a month a go and it didn’t seem to help. Fuel pressure seems like a likely candidate to me. Yes I’ve read all the forums too but none have seemed to help me. I do appreciate all you guys help. A case of beer to whoever has an answer. Lol.

I had the same issue with a lot of soot and it turned out to be the blend of fuel I was running. I switched to 87 octane and it greatly reduced the amount of soot. I would also suggest to check your fuel pressure. You could have a bad pressure regulator causing it to run rich. The 500 efi is a speed density tune with no 02 sensors to regulate the fuel trims based on what’s coming out the exhaust. Just my 2 cents. Good luck and hope you sort it out.

Hose for MAP sensor leaking?

Can you get a scanner on it and see what the sensors are reporting?

Anything over 87 octane burns to slow for these engines leaving a ton of unburned soot out of the pipes.