1999 Mercury 200hp EFI SN#0G897131

[Bassin1206]

My boat was running great until about 2 months ago. I would back it off the trailer, it would start and idle just fine, but when I would accelerate it would bog down and would get on plane. The first few times I went out and it would do this I could put it in neutral and try again and eventually it would start going. Once on plane it would run great. Each time I went out it seemed to get worse and eventually it got to where it wouldn't get on plane at all. After several tests I pulled the plugs and the lower port side cylinder had water in it. I pulled that head and replaced the gasket. The old one didn't have any obvious signs of leakage, except for one tiny spot it looked like water was passing through. Once I replaced the gasket it cured the water leaking into the cylinder, but the performance issue causing the bogging down is still there. About two years ago I had some other issues with it starting and I had to replace the stator, both power packs, the trigger and the voltage regulators so those items are only two years old. About 6 years ago the ECU was sent off and the driver circuits were fixed and the injectors were cleaned and calibrated.

From everything I have read this issue could be electrical or it could be fuel related. Since all of those electrical components were replaced two years ago I thought it might be fuel related so I've been looking in that direction. Is there a check valve on the pickup tube in the fuel tank that could be causing the issue or any other areas of the fuel system I should focus on? I've replaced the fuel/water separator and the spark plugs with no change so I'm looking for recommendations on where to start troubleshooting this issue.

Any advice is much appreciated.

[JOE54]

mabe anti syphon valve at connection , would see what fuel psi is doing first ,make sure all are firing also

[Bassin1206]

I forgot to mention, I verified all cylinders are firing. Where is the anti siphon valve located?

[JOE54]

some have it some don't should be in barb fitting where fuel line connects to tank , I don't think its yo problem though

[Bassin1206]

Would bad switch boxes (power packs) cause it to bog down to the point of not accelerating? When I replaced those parts a couple years ago I replaced them with Mercury parts, not aftermarket, but they could have gone bad I suppose. I’m trying to find things to try before taking it to a mechanic. Last few times I’ve taken it to a mechanic they couldn’t find anything so I had to take it elsewhere or keep trying things until I found the issue so I’m trying to figure out what are the most likely items to try first. I appreciate any information.

[JOE54]

could but you said its firing on all six , Got access to another ECU that's a known good one ??????? possible inj driver bad

[indy390v]

Just guessing, but mine was doing very similar thing and ended up being very simple fix. I had a loose and dirty Positive cable connection. Would start fine and idle around fine. Put it up on plane and it would loose power and cut out and die. Mine was easy fix, hope yours is too.