I am looking for some guidance on a 525 engine issue. The engine only has 25 hours at this point and has not ran correctly since new. For the first 5.9 hours, the engine would not run over 4600 rpm and continuously misfired or studdered as I call it. It sounded like the rev limiter was on at all times. The dealer looked for codes, however, none were found. Around 6 hours the engine started to run up to 5200 rpm, however, it still studders when accelerating, when running between 2500 and 3500 rpm, and when under a load like pulling a tube full of kids. The engine will run along studdering and after a few minutes, it will smooth out and the rpms increase 300 to 500 rpms without touching the throttle. A few minutes later, it starts studdering again and the rpms drop. Also, on some occasions, the gauges cycle from the top of the scale to the bottom of the scale as the needles quiver while running down the lake. Shutting down the engine and restarting correctes the gauge issue. Mercury has troubleshot the engine a couple of times and cannot find any codes in the computer or and other issues. Sorry for the long post. Any ideas????? Thanks

Might want to ask this in the technical Q&A section...Those guys usually offer a lot of help...

The gauge issue makes me think you have a bad hot or ground lead. The main harness plug can be a source of problems. Make sure it's coated with dielectric grease and making firm contact on all pins and leads.
Make sure your battery leads are tight, and that you don't have a dead cell or internally broken post. Check the Perko switch wiring and make sure the lugs are tight. Also check your alternator and leads to it.
Good luck.
Steve

Sounds very similar to a problem I was trouble shooting a few weeks ago on a Howard Bullet. The owner said he'd been fighting this problem since new. It had 60 hrs. on it. I spent about 10-12 hrs. checking everything, running it at the lake and on the dyno. Never did fix it. I truely believe it was the PCM but I could not get a replacement to find out. The owner finally decided to trade the boat in on a new one because he was so bummed with it. Must be nice to have the means to do that. Your gauge issue sounds like a bad ground. But it's just about impossible to check them all with the engine in the boat.

I won't and can't post it publicly.

But if anyone wants my insight into a difficult situation working
with Mercury Marine then email me at:

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Pesky Varmint

its either a ground wire thats loose, a fuse or wire thats shorting, or the PCM is whack....either way you only have about 500 ft of wire to check. sucks

Who from Mercury did the troublshooting?

Was it a Mercury Service center or your dealer?

There should be a regional Merc Racing rep that service your region. They are very very good about finding issues that the local service center cannot. The gauge thing does sound like a bad ground, low voltage or main wire harness issue.

Thanks for all of the tips. The regional Merc Racing rep was here Friday troubleshooting. We were able to repeat the gauge issue. He believes the problem is in the digital to analog control box. No issues were found with the engine. Of course, it ran without dropping rpm the entire time he was on the boat and for the next 2 days.