Trim gauge is going haywire

[bucket mouth]

A new problem has arisen with my 2007 250 pro xs. My trim gauge seems to be all over the place as soon as I start to plane off. I have also noticed that it won't trim as high as normal unless I'm at an idle. I know that under a load that there is a maximum that it will trim, but with it bouncing up to a quarter and then down to nothing, I just assumed it was the gauge. However, when I looked behind the boat at the rooster tail, it wasn't as tall as normal and I could tell it wasn't trimming as high in the water. When I come off plane, I know that it is trimmed a little because the gauge kinda goes back to normal and will jump up and read accurately again. I'm thinking that it's probably a ground issue, but I can't figure out why that would prevent me from trimming up normally at an idle, but not when on plane. I'm also stumped as to why it works a little but not more. Any help would be appreciated.


Modified by bucket mouth at 7:20 PM 10/9/2011

[EuropeanAM]

The trim gauge problem could be either a faulty sender, OR a DAMAGED GROUND STRAP between the lower engine mount bolt and midsection/swivel bracket.

This ground strap is MANDATORY (otherwise, there is no continuous ground supplied to the midsection).

I would stronly recommend that you have your engine mounting hardware, any jackplate, transom bolts, steering hardware, and engine midsection inspected.

Changes in available trim angle (as evidenced by your comments regarding performance and "rooster tail") are usually an indication that something has (or is) moving. This is not good- CONSIDER IT A SAFETY CHECK.

Hardware torque checks should be part of your REGULAR MAINTENANCE SCHEDULE.

http://www.bbcboards.net/zerot...gines

[bucket mouth]

Don, thank you for the quick response. I've checked all bolts around the jack plate and mounting hardware, as well as steering components. Can you give me a little more direction on how to locate this ground strap? I'm assuming it's located on the front of the motor, do I need to remove the cowling to gain access to it, or is it on the outside? Thanks for all you do.

[ssimpala71]

Port side lower motor mount to swivel bracket. About 6 inches in length.

[bucket mouth]

Thank you ssimpala. I found a round metal something on the port side with a wire coming in from the starboard side and another wire coming out the back that looked like a ground. Thanks for your help

[EuropeanAM]

You're looking for #9 in the following parts diagram (on the opposite side of the engine):

http://www.mercurypartsexpress...r7727


It will attach to the large nut for #9 in this drawing (lower mount swivel yoke):

http://www.mercurypartsexpress...r7725

[bucket mouth]

Thanks for the help. Would this be my problem?

[EuropeanAM]

That would likely be the cause of the problem.