Intermittent Trim issue - late 80s Mercury 115

[Jaybird73]

Here's my situation, apologies for any extraneous info: I've got an older boat with a late 80s model Mercury 115 outboard which I only take out a handful of times per year. I changed out the side control box last year. Everything ran fine past year except for old throttle and shift cables which I knew needed replacing. Had not run it this year until the Fourth. Started tinkering on it and cleaning a few days ahead of time. I had to replace the shift and throttle cables which went in without a hitch.

On the 3rd, I Charged the battery and tried the trim and only got clicks when tried in each direction. Went and bled the system and it trimmed and tilted fine in both directions. Starter and test ran the motor and everything was fine with it beyond burning through a little of last year's fuel.

Came back on the morning of the 4th to check everything again and give it a quick touch up cleaning. Motor is still fine. Trim was now not operating, only clicking when engaged in either direction. I moved the pin on the outboard mount and went and had a pleasurable ride that afternoon just without operable trim.

Went back to it earlier today on my lunch break. Double checked all my fuses and bullet connectors. Tried the trim and it worked fine in both directions, several times. Tried it again when I got home from work and the down trim engaged once briefly, otherwise just clicking in each direction.

I have no idea how old the trim motor is or if it has ever been changed. My gut instinct is that it's now time to replace/rebuild the trim motor. Suggestions to try before going that route?

Also, if I do need to take it off, must I drain the hydraulics first? And is it better to remove the whole single tilt, double trim cylinder assembly or just take off the trim motor while it's still mounted?
Thanks in advance for any advice or tips.

 

[Jaybird73]

I also left out that I went and tried bleeding the system again multiple times on the morning of the 4th.

 

[Jaybird73]

I also left out that I went and tried bleeding the system again multiple times on the morning of the

 

[Chris1956]

So, the PTT system is the trim pump/reservoir in the boat and twin trim cylinders outboard of the transom bracket?

I think the problem is electrical supply to the Trim Pump motor. You can test this by using a jumper cable from the battery positive post to the green and then blue wire that run to the pump motor. Jumper to the trim solenoids, green wire is for down. Blue wire is for up. Don't forget to jumper from the battery negative post to the black wire on the trim bracket, where the black wire from the trim pump attaches.

If the trim functions normally, somewhere the electrical connections are bad or something is not working. I have had to replace a trim button on that system, even though they are solid copper/rubber. The trim limit switch is probably bad by now, and should be bypassed.

If still not consistent trim action, then the trim motor is suspect. Those are hard to find to replace them. There may be a few NOS laying around.

If a starter shop will rebuild it, that would be better. I would unbolt the 4 hydraulic hoses at the pump and take the whole pump/reservoir in for repair.

The hose connection to the trim cylinders often strip, hence leaving them connected.

 

[roscoe]

Is this an inline 6 cylinder motor?
Some of those still used solenoids to activate the trim motor.
There are a lot of wires connected to the solenoids.
Make sure all are tight including the grounds.

 

[Jaybird73]

So, the PTT system is the trim pump/reservoir in the boat and twin trim cylinders outboard of the transom bracket?

I think the problem is electrical supply to the Trim Pump motor. You can test this by using a jumper cable from the battery positive post to the green and then blue wire that run to the pump motor. Jumper to the trim solenoids, green wire is for down. Blue wire is for up. Don't forget to jumper from the battery negative post to the black wire on the trim bracket, where the black wire from the trim pump attaches.

If the trim functions normally, somewhere the electrical connections are bad or something is not working. I have had to replace a trim button on that system, even though they are solid copper/rubber. The trim limit switch is probably bad by now, and should be bypassed.

If still not consistent trim action, then the trim motor is suspect. Those are hard to find to replace them. There may be a few NOS laying around.

If a starter shop will rebuild it, that would be better. I would unbolt the 4 hydraulic hoses at the pump and take the whole pump/reservoir in for repair.

The hose connection to the trim cylinders often strip, hence leaving them connected.

All three cylinders and the trim motor are mounted outside the transom between the brackets.

 

[Jaybird73]

Is this an inline 6 cylinder motor?
Some of those still used solenoids to activate the trim motor.
There are a lot of wires connected to the solenoids.
Make sure all are tight including the grounds.

Yes, inline 6.

 

[Jaybird73]

I took it out yesterday. I've got other electrical issues now. Charged the battery yesterday morning, hooked up the hose to the lower unit, and started it up in my driveway just to make sure she wanted to fire up. Took longer than it should, but eventually cranked and ran strong. I let it medium idle for a few minutes to warm up good. Then topped off the battery with the trickle charger.

Went and put in and it ran well initially. Motor runs really strong on it. Floated for a bit after running probably 20-30 minutes. Started but it didn't start immediately. Then Got caught out on the water in a storm. Floated for awhile after the storm and tried to restart. When turning the ignition on, it didn't want to turn over. Sounded close but it wouldn't hit. Then when I tried to turn the switch off, it wouldn't stop. Had to undo a battery cable. Turned the switch back and forth several times just to try to make sure it was off. Hooked cables to my spare battery instead of my primary. Same result with motor trying to crank and ignition switch turned off as soon as my second battery cable touched its terminal and made the circuit.

Again, this was a brand new OEM box installed last year. I did have to dismount and remount it to install the new throttle and shift cables at the bottom of it 10 days ago, but the trim and ignition wires are all factory prewired and the engine cable was already factory reattached. Just had to plug and play it back on the motor last year.

 

[Chris1956]

OK, too many problems to diagnose at once, with the description given.

First of all, what year is motor? Does it have 50cent piece-sized round electrical connector or external quick disconnect plug on motor?

Check engine wiring harness for failing insulation.