SOLVED after seven years: Outdrive trim works at idle, but not when on plane

LaRea

[EDIT:  This problem was caused by a trim sender that was not installed correctly.  Here are the key facts:
*  Mercruiser systems with DTS have an outdrive trim limit that is linked to engine speed.
*  If the engine is above 2750 RPM, the software does not allow trimming the outdrive up past a certain level (I think 50%).
*  My port drive trim sender was not installed correctly.  It was reading 54% when the drive was all the way down.
* Therefore, although the trim worked fine at idle, it would not operate at high RPM.
[END EDIT]

This problem inherited from the original owner is still unsolved after 7 years.  Somebody please help me!

• 2008 370 with Merc 496, Bravo 3 and DTS
• At idle speeds, both drives trim up and down and sound normal
• After the boat is on plane, the stbd drive will trim up, but the port drive will not 
  
• It doesn't matter how long I press the trim button
• The problem was originally on the starboard drive
• When I swapped trim pumps, the problem moved with the pump to the port side
• Parts I have replaced on port side:  trim pump, up solenoid, hydraulic cylinders
• Converted both drives to digital trim indicators

What else can I possibly try?  It can't be the switch at the binnacle, because the problem moved when I swapped pumps.   

Once during winter layup, I had two heavy guys hang on the outdrive.  The drive was able to lift them both off the ground easily.  Why can't it lift when I'm planing?

This problem is bugging the crap out of me.  Besides the obvious fuel impact of not being able to properly trim the drives, my inner OCD self just HATES having something on the boat that doesn't work.  

Here's the original thread.
https://rinkerboats.vanillacommunities.com/discussion/3380/outdrive-trim-works-at-idle-but-not-when-on-plane

Handymans342

I would verify voltage at the solenoids while underway and eliminate that part. 

Handymans342

I remember that my manifold where the lines hook up under the mercathode was clogged. 

LaRea

Handymans342 said:

I would verify voltage at the solenoids while underway and eliminate that part. 

Okay, I could run a wire up to the cockpit to check it underway.  It's just odd that a voltage issue would move with the pump.  

Handymans342

I would flush all the lines as well. Maybe over the winter. 

Handymans342

LaRea said:

Handymans342 said:

I would verify voltage at the solenoids while underway and eliminate that part. 

Okay, I could run a wire up to the cockpit to check it underway.  It's just odd that a voltage issue would move with the pump.  

Well then it has to be the pump. 

Michael T

@LaRea yeah, that would make me nuts too and 100% you need it for proper planing and fuel efficiency. Have you replaced the trim senders. Can you check the line voltage to the trim units when underway? Have you checked grounds? There MUST be a logical solution to this. I have never heard of this fault before. Have you contacted the Mercruiser help line? Could the attitude of the boat on plane be affecting the level of the fluid in the senders? Can you tilt the boat on land to approximate the attitude on plane? 

LaRea

I replaced both trim senders with digital when I did the helm upgrade.  I checked all of the grounds at the same time, because I had to add a second ground bus bar in the engine room. 

If I'm planing with both drives all the way down, the pitch and roll angles are normal, but the port drive won't budge.  If I trim the stbd drive up a little, the boat rolls to starboard, so I have to level it with trim tabs.  That works, to a point.  

When I spent $500 on a new pump, I was *sure* that was the problem.  When I then replaced the up solenoid, I was *positive* it would work.  

YYZRC

It seems like the trim limiter could be coming into play but I can’t explain why that would follow the pump. Easy to bypass to test. Are the trim senders original?

LaRea

@Michael T maybe I should call Merc and see if I can drill down to one of the senior engineers.  

davidbrooks

While on plane try pushing the switch all the way down to "trailer mode" and see what it does. Your logic is sound on what you have done so far. Now time to look for things that make you scratch your head.

LaRea

The trim buttons on this DTS binnacle don't have a trailer mode.

RustyS

Just had a similar incident on a buddy's boat.... 
@YYZRC nailed it; the trim limiter for some reason came out of adjustment. No reason, but after adjusting it all was fine.

LaRea

Just got off the phone with Merc.  They suggested the same thing, but it doesn't make sense.  In 2015, I swapped the pumps port-to-stbd, and the problem moved with the pump.  I didn't change the trim position senders until 2016.  

For sure, I'll adjust them when I haul out for the winter.  

YYZRC

You can pull the bullet connectors for the trim limit sender (on the transom harness) and jump them together to disable the limiter for testing. Pretty easy and on my boat they were well marked. 

LaRea

I did learn a thing:  there is a trim limit that depends on RPM.  Above 2750 RPM, the drive won't trim up past a certain level.  In theory, if the position sensor is out of adjustment, the drive would do what I'm seeing.  But there's no reason it would follow the pump when I swapped it.  

Michael T

@LaRea that makes sense. The drives should, I believe, trim right up to trailering without being stopped. The reason for this is to keep them within the sweep of the guard pieces on each side of the drive. BTW if the problem moved with the pump (did I read that right) I'd be giving the evil eye to the pump! Pls keep us posted. Again there MUST be a logical explanation. Man are you going to enjoy that boat with both trims performing to spec.....made a huge difference to my 310 and 360! Huge!

Handymans342

I’m actually driving up this weekend to fix this problem for him MT

Handymans342

And if I can’t fix it I plan to consult with @Alswagg over some man drinks to solve this issue after I consult with @randy56. You see there is nothing I wouldn’t do for a Rinker brother in need. 

LaRea

The first step was I rebuilt the pump, no luck.  Then I swapped the pump, problem followed the pump.  Then I replaced the pump, and the rams, and the solenoid, no luck.  Only @Handymans342 can solve this problem.  

Handymans342

You have all kind of suggestions now which path will you take??

randy56

I agree with YYZRC

LaRea

@YYZRC showed me how to view the trim position calibration on my VesselView 702.  Something ain't right.  I think my trim sensor might be miscalibrated.

Looking at the VV display with engines off, I moved each drive through its full range of motion.  On the starboard drive, the range is [1.5 - 100.0].  But on the misbehaving port drive, the range is [54.9 - 100.0].  When the drive is physically trimmed all the way down, the lowest reading is 54.9.

Now, these numbers appear to be percents.  They are not the raw sensor ADC counts.  Merc says raw counts can only be read by a Merc dealership, and the range would be something like [100 - 650].  The VV shows whatever the engine computer spits out over SmartCraft.

Apparently, the engine computer thinks that the port drive never goes lower than halfway down.  If that's true, then once I get above 2750 RPM, it would say "I refuse to raise the drive any higher at this speed."  

I'm scheduling a short haul to check my trim sensor.

YYZRC

It sounds like the sender is working fine, it's just out of adjustment.

Not sure if you feel like a swim, but I've adjusted mine in water very easily.  Turn the drives so the starboard side is exposed and then all you need is a Phillips screwdriver to release the screws and rotate slightly.  A tiny rotation results in a significant change in the reading - I had the admiral at the helm shouting the readings to me as I rotated the sender (ignition on but engine not running).  Snorkel recommended.

Dream_Inn

I agree, it's an easy adjustment without the haul.  Too bad you didn't have any friends around with a lift that is close by.  I think the gas to my place would outweigh the short haul cost.

LaRea

Heh ... well, I do need to haul out for a hull cleaning.  If I can't do it this week, I'll be anchored in shallow water on Saturday with a screwdriver in my hand (the tool, not the tasty beverage).

F1100

Perhaps its the limiter on the drive, when underway it has stress on it, and perhaps is moving. While at idle no stress, so not moving the limiter.

MarkB

When we want a trim to go up, isn't it effectively lifting the entire boat hull out of the water? So isn't it putting a lot of force on the drive?

Here's what I would do ... at idle RAISE both up and leave them up, then floor the gas (safely) ... so if you can get that problematic drive to LOWER. 

My theory is, it should lower, but not trim up ... that means the pump isn't providing enough pressure to overcome the force it needs to lift the bow out of the water.

LaRea

Well, the rams are pushing against the propeller thrust, which takes a lot of force, but I don't think lack of force is my problem.  My drive can easily lift at least 300 pounds of boat yard workers.  I mean EASILY ... with two guys hanging on the outdrive, there was no difference in speed or sound.  

I never knew there was an RPM-based trim limit, and might never have found out except I talked to a really good tech at Merc (thanks @Michael T for that suggestion).  That HAS to be it.  Nothing else makes sense.  

I hope to find out this weekend.  

Handymans342

With me on board???

LaRea

Be at my place Saturday around ten!