trim pump help please

[2ifbyc]

OK guys here we go again... 1990 Cobalt with mercruiser 454 mag 7.4l and bravo 3 OD. I just had the outdrive replaced brand new with new trim sender and limit switches installed. Today I adjusted them and everything is working fine as far as the trim gauge and trim limit. The problem I am still having is this... The trim and tilt works fine at the dock and at low speeds. As soon as I take off or while i'm at high speeds the trim DOES NOT WORK!. Its driving me nuts. I get back to the dock and it works fine again. It seems as if the pressure isn't strong enough to lift the drive while i'm underway. Its definitely trying cause I see the battery gauge draining power when i push the trim buttons. Is there a test I can run to troubleshoot this? Has anyone experienced this at all? How do I know if its the pump motor, solenoid, valves? Is it possible that the grey and black hydraulic hoses to the trim pump got reversed somewhere? As of now the gray is on the right and the black is on the left but I dunno if the mechanic reversed them on the drive possibly or if this is even a possible solution??? Any help would be greatly appreciated. Im going nuts with this one..

 

[cr2k]

Re: trim pump help please

How do you know it doesn't work underway? Is someone looking when you try to trim? You pressure relief in the pump may be stuck or dirty or your pump motor may be weak.

 

[2ifbyc]

Re: trim pump help please

Yes its very obvious that the boat is not trimming while underway but it works fine when Im either not moving or moving slowly.

 

[Bondo]

Re: trim pump help please

Is it possible that the grey and black hydraulic hoses to the trim pump got reversed somewhere?

Yes...

 

[2ifbyc]

Re: trim pump help please

Bondo, any advice for troubleshooting this. The manual talks about testing with a pressure gauge, which I don't have. Any ideas from anyone? Can I just switch the black and gray hoses at the pump? How do I know which way is right now!

 

[swihartart]

Re: trim pump help please

I have an older 1977 prestolite pump. The gray line goes to my reverse lock and the black goes to the bottom of the pump dog bone.

I troubleshot for a loooooong time of why my drive would not trim up while the shifter was in neutral. groaned really bad and just wouldn't move. It would go down fine but move a little going up and stop and strain the pump.
Changed cylinders, hoses, pump etc. same thing.

One day just by accident it was going up and down fine out of the water (I didn't want to take it back out not working properly, lost all last season, my first year owning one, sand bar started the whole ordeal )

I looked to see what had changed...the shifter was in forward! so I traced what that changed and it puts the reverse lock in a different position on the shift plate.....uh - huh, reverse lock is out of adjustment, fixed this and never a problem again.

Could it be (this depends on what pump you have...I think the reverse lock is built in to the newer oildyne) that the shift position influences your reverse lock? Faster = not working.

And will it go down but just not up while fast?
Just an idea...the manuals are available in the sticky at the top of the page, it will have a diagram of your hose setup.

 

[Don S]

Re: trim pump help please

 

[2ifbyc]

Re: trim pump help please

On I have that photo in the service manual. They are in the correct position on the pump now. I was asking if they got reversed possibly at the other end? If so can I just switch them at the pump to correct it?

 

[rfdfirecaptain]

Re: trim pump help please

I see you have the right guys on the job to solve this one, but I need to get some postings under my belt.

I had the exact same problem last year. Same symptoms as yours. Working then not working when underway.

Here's what I did. I had to replace both of my trim cylinders. I noticed the boat was not handling correctly. While underway I had my wife driving and I was looking over the stern. At about 25 Mph and with the outdrive in a fully down position, I noticed my outdrive was flopping up and down about 2-3 inches which immediately indicated to me that there must not be any pressure on those trim cylinders.

If my drive was flopping, that means the water pressure hitting it as we were underway was a stronger "tension" than the "compression" which was being applied to my cylinders by the force of the rotating outdrive. One would think these forces to be equal and when underway at a steady speed I would agree with that, but as we all know driving a boat is an off and on the gas style of driving.

At first I thought it was in the hydraulic pump. It worked fine to raise the outdrive when I hauled the boat out of the water. On the way home I stopped for gas. That's when I say the skegg sitting about 2 inches above the roadway. I lifted it and tied it them brought it home where I had the pump pressure tested and the cylinders vacuum tested.

So, this leads me to my point. By my own trial and error, I would think that if it's working when not underway your cylinders could be on the verge of failure as mine were.... just not strong enough to push out and hold their position against the forces of tension and compression while underway. After all the cylinders don't work off of a mercury switch like a thermostat so it makes no sense that they don't work when underway and at a more inverted attitude, unless there is some force that is being applied that is not being applied at other times.

 

[2ifbyc]

Re: trim pump help please

Bondo or don? Any ideas? Should I try switching the black and gray hoses at the pump? I also noticed after the drive was installed that up trim was down and down was up. I have since reversed all the up solenoid wiring to the down and vice versa. Is it ok to just reverse the black and gray hoses? If not then what should I do. I'm pretty sure my cylinders are ok.

 

[Bondo]

Re: trim pump help please

I also noticed after the drive was installed that up trim was down and down was up.

Ayuh,... Then I would Guess the Lines are Backwards,... Swap 'em...