Black Scorpion Question

I have a 2005 Sanger V215 with 330hp Black Scorpion. It idles fine and sounds great getting up to wakeboarding speed. Once moving at 17-22mph, it makes popping noises out the exhaust. The RPM's reduce slightly when the pop is heard. Perfect pass usually kicks in adding throttle and the popping goes away. It seems to pop when reducing throttle. At the end of last season, I took it in to a mercruiser dealer. He said it needed a tune up. Changed cap, rotor and plugs. The popping wasn't as loud, but did not go away. They said the computer did not read any problems. I had another mechanic come to the lake with a computer to hear it under load. His reading on the computer was that the MAP sensor was reading 9 for barometric pressure. We replaced the MAP sensor and the Throttle position sensor. MAP sensor was now reading 13 for pressure. I'm not sure what this is supposed to read. I called the mercruiser dealer and he said this reading can vary by boat. When we took it out for a drive under load, the sound continued. He told me that the sound was from water in the gas and that it would work it's way through. I pulled the fuel water seperator and there was no water in it. I replaced it as well. Next step will probably be to change the inline fuel filter. Is it possible that I have an intake manifold gasket leak? I would think that extra air running through the intake manifold would lean it out and cause it to idle at a higher RPM ro there would be other symptoms. It's only got 150 hours on it, so I would hope that's not the issue. Anyone else had a similar issue? Any ideas? Summer is here and I'd sure like to get it running better. It's really frustrating when eveyone says the computer readings look OK but it's not running well.

Thanks.

Popping in the exhaust would usually be air getting into the exhaust side and/or unburned fuel igniting.
I have 200 hours on the 330 Scorpion in my '06 (engine actually built in '05) without any issues like that. My little rubber scorpion came loose on the intake but that's not really related.

I forgot to mention that I changed the IAC filter as well. The filter was pretty dirty with soot. Possibly from exhaust? How would I go about determining if there is an exhaust leak causing the issue? Would it be a possible stuck PCV valve?

Don't know if boat motors have PCV valves...

To check the intake have the boat running at idle and spray carb cleaner around the base where it mounts on the engine block. If there is a leak it will idle higher when you spray. An exhaust leak would not cause popping and would be extremely loud on the side that was leaking.

I'll give the carb cleaner a try. If it's not an intake leak, what would be the next most likely culprit?

Take a look at your rotor and cap
Mine did something very similar the cap and rotor where corroded and needed to be replaced

At the end of last season, I took it in to a mercruiser dealer. He said it needed a tune up. Changed cap, rotor and plugs. From his post.

For it to be popping most likely a fuel/mixture problem. If not the intake it could be injector/s

post was tooo long to read

Rob, like Kevin said take the 2 minutes pop off the cap on the distributor and look at the contacts the contacts might be corroded. Mine did it over the winter had deposits on the terminals inside cap. Also pull your plugs and take a look they will tell you if your rich, lean, possible misfire or if you have a bad injector. You can tell allot about a motor from plug color. By the way should be a light tan color on the plugs if running right. To me sounds like a secondary ignition problem. Also check wires at cap and plugs some times the wires don’t snap on tight and over time from the arc of the spark jumping from electrodes will erode them and cause misfire.

Thanks for all the info. I pulled all the spark plugs. They were all light tan and looked good. I made sure the wires were all tight when I put them back. I pulled the distributor cap. The rotor looked fine, but all the contacts on the cap had a green streak of corrosion on them. I scraped the corrosion off with a fingernail. There wasn't much. I relaced the cap and made sure the coil and ignition wires were tight. I'll take it out tomorrow and see how it runs. Thanks for the help to this point.

I checked all the vacuum tubes connected to the intake manifold. Everything was in order. I'll try to carb cleaner around the manifold tomorrow if the distributor cap isn't the issue.

First thing is to check the timing. Make sure that is to spec.

If it is, you may have a problem with an exhaust valve. Either a valve is burnt or carbon deposits are affecting the valve guides or valve seating surface. my .02

I sprayed carb cleaner around the intake manifold. It's hard to get too close with the black scorpion top so close to the valve cover and all the hoses stuffed in there. From what I can tell, there are no vacuum leaks.

I assume I need to take it in to have the timing checked. Would that have showed up as a problem on the computer diagnosis? If it is an exhaust valve problem, how do you diagnose that?

I still haven't changed the inline fuel filter. I'll try to get that done this afternoon if I can find the part.

There are products that you can buy to decarbon the engine. Including fuel additives and products to attach to pcv or vacuum line to clean carbon deposits.

A cheap way is get yourself a small water bottle. Put your thumb over bottle opening. Bring engine up to 2000-2500 rpm and slowly and I mean slowly pour water into intake. When engine starts to bog stop pouring water and let engine get back to speed. Repeat several times. Then drive boat hard for 5-10 mins.

I changed the inline fuel filter today. It ran significantly better. It's not perfect, but getting there. I cut the old filter apart to see what it looked like. It looked brand new inside. Nothing inside to clog it. Is it possible that something is clogged in the pick up tube in the tank?

I'll run it for a while tonight and tomorrow to see if the issue comes back after a couple of hours.

After changing the inline fuel filter, it ran pretty good for a couple of trips up and down the lake with ballast full. Then it started again. If I have bad gas in the bottom of my tank, is it possible to just pull the fuel filter back off and drain a gallon or two, or do you need to pump the bad gas out somehow? Would this make sense if I've already run through a full tank this summer and used stabilizer?