Merc part number 17631A1, list price $42.10. Any Merc dealer should have them.

Thanks Mr V, I'll order a set and see if that helps.

Check BAM for a discount.
http://www.go-fast.com/trim_pumps.htm

I was looking on their other website. $490.00 is a great price.

Thanks,

Check the simple things first if not already like where the trim limiter is set. Maybe limiter is shorting out when drive is under load vice hanging in the driveway. Does it trim up if the trailer button is used while running at 4500rpm? Fluid level? I'm only suggesting becuase I haven't read what you've done to try and isolate it. My experience with boats has always been to methodically go thru the simple crap prior to thinking on a more complicated level. Good luck.

An easy way to remember the wiring on the pumps is this; Blue=Sky (up), Green=Ground (down).....

I've seen the cylinders go bad more than the pump itself but, you've got to check both.

Thanks guys,

Didn't think to try the trailer trim button, The trim limiter could easily be part of it. Fluid is ok, i assume rams ok because no fluid leak and does not bleed down once up.

I will be checking all the possibilities listed here tonight and then trying a brush set.

Are you sure the trim pump is running when you try to trim up at 4500rpm? Check that first of all. I had a similar problem last year.

What caused it was that the trim cables in the throttle control got short cutted above a certain angle of the throttle control...

Thomas, It sounds to me like the pump hoses are reversed. If you need a pump go aftermarket discount marine site. I got mine for 300 a piece two years ago. On your pump hoses you can switch them on the bottom of the gimbal housing at the hose manifold. I had the same problem a couple years ago when i put mine back together. It would trim till I hit the throttle, then theprops would push the drives back towords the transom.