Problems with brand new Mercruiser 383 MPI

[Rogerdog23]

Just repowered with a 2020 Mercruiser 383 MPI and am having performance / excessive fuel burn problems.

Here are the quick details:
—24 foot Sea Ray that had a 350 Mag MPI
—Haven’t touched the props or Bravo III drive (same as before repower)
—Went from burning 11.8 gallons per hour at cruise to 17 gallons per hour (same rpm)
—Top end RPMs went down by 200 and top speed is down 2 miles per hour
—New engine has 30 hours on it and is a brand new, not a remanufactured.
—New engine added 50 horsepower (from 300 to 350)
—Boat is on a trailer so no issues with dirty hull slowing things down
—Hooked up VesselView Mobile and got an engine sensor error code. Engine or drive trim position—the input circuit for the sensor is above the valid limit.


Any ideas on what in the heck could be going on? Could the trim sensor error put it in guardian mode? Not sure that would explain the excessive fuel burn if so.

Working with Mercruiser for warranty but that is a long slow process this time of year and i want to get out on the water again.

 

[Rick Stephens]

I wonder if the ECM has to be reprogramed for the little bit bigger motor?

 

[Rogerdog23]

I got a full new engine package complete with everything but the outdrive so I think the ECM should be good to go unless I’m missing something?

 

[Scott06]

I got a full new engine package complete with everything but the outdrive so I think the ECM should be good to go unless I’m missing something?

If you got a complete bobtail vs a long block and swapping old components over you’re fine.

only thoughts would be to check fuel pressure is ok and knock sensor isn’t retarding the timing constantly. I assume no other error codes are showing? To eliminate the trim sender swap a good one in, can be done in engine compartment to fake it out and see what happens.

 

[alldodge]

New bobtail what about the dealer you bought it from?

New motors might have missed something when building.
I would start with checking timing. Check plug wires to ensure there correct. Pull plugs to see if maybe the plug gap was damaged on install

 

[Scott Danforth]

new motor comes with warranty if installed by dealer.

 

[Rogerdog23]

Scott06 good idea on faking out the trim sensor. That should at least make the alarm go away and let me see if any kind of 10% guardian mode was in play. No
other error codes showing.

I checked plug wires and the basics but am waiting for dealer to do fuel pressure, timing etc. Not sure how long of a wait I’m in for.

 

[alldodge]

The trim sensor will always be there and is not an issue because you probably don't have digital trim.
You mentioned an alarm, is it just an error or an alarm?

 

[Rogerdog23]

Alldodge can you explain the digital vs analog trim options and how to ensure they are wired up properly? The bravo 3 is a 2006 model but the engine is 2020 complete bobcat with EVERYTHING included. Not a reman from mercruiser but brand new block From Mercruiser and all new everything ($15k).

Before I switched to the VesselView mobile I was using the original SmartCraft gauges during engine break in. I received an actual alarm (loud beeps) and the led display at the bottom of the SmartCraft gauge said “trim fault error”. This happened several times. I took it to the dealer who installed it without an appointment and they hooked it up to the computer really quick and saw the trim error but were unable to clear it. Last weekend I switched to VesselView mobile and it showed the error I mentioned in the original post. My gauges are disconnected now that I have the VesselView plugged in so I can see if I’m still getting an alarm on the SmartCraft gauges.

The dealer will look at it eventually but they are crazy busy and it will be a while. Meanwhile I’m burning 17 gallons an hour which is 25% more than I should be burning and I’m slow to get on plane when the 383 stroker is supposed to be a torque monster. Instead it’s worse than the 350 mag.

 

[alldodge]

Being a 2006 you may not have digital trim. Digital has only one sender and its on the starboard side of the gimbal

Since this is a 2020 motor, meaning its using PCM09 software or higher. Smartcarft can be programed in prior years to disregard the trim fault, but could be in 2020 its no longer be bypassed (or null the value)

Hey muc have any insight into this one?

This when I tried to go digital to analog, shows transom assembly with the sender, has 3 wires

 

[Rogerdog23]

Thanks. I confirmed With Mercruiser it is not digital on the engine (small block and not fly by wire). On the outdrive I have the limit on the port side and sender on the starboard side if that helps. The engine harness has the option for digital or analog where the bullet connectors go. Not sure if that helps wanted to pass it along.

 

[alldodge]

Your getting an alarm for digital trim but the motor does not have it

Older versions of Smartcraft programming makes adding or removing things like trim accessible to user, in 2020 I don't know if this remains the same.

 

[QBhoy]

Couldn’t just be that it needs running in and quite a tight engine, being new ?

 

[Rogerdog23]

New news: Found a cut red wire probably 14 gauge in a black conduit on top of the engine Near flame arrester, coming from the back of the engine. Engine cover was crushing me and didn’t have a partner to hold it up so couldn’t see where it was coming from or if there was a stripe on the wire. Clean cut but no factory terminal on the end or electrical tape. Looked like there were a handful of similar wires in black conduits as well but this was the only cut one. Any ideas? Can investigate more tomorrow for details on where it is coming from.

Mercruiser said the digital is needed on the engine basically as a bypass to the SmartCraft gauges if that makes sense. I’ll test the ohms on the sensor tomorrow and see if it can be adjusted or is just shot. I’ll also try The suggestion of trying a new sensor without actually installing on the outdrive. I have the part and should be fairly easy to try if the current sensor proves to be faulty. Merc also suggested trimming all the way down then down again for 5 seconds to reset the counter on the trim sensor.

Mercruiser doesn’t think it’s a tight engine with all the symptoms. Said at 20 hours you get most all of the fuel efficiency and performance.

Any other ideas holler and I’ll try when I get to the boat tomorrow. Will report back if it gets fixed too...not a fan of fix and not reporting what the issue was.

 

[alldodge]

No idea on the wire as yet

 

[muc]

Got a serial number so we can look up what ECM you have?

 

[Searay205]

boattest.com did a test with your new engine in 6K lb boat. It averaged 3mpg at 3K rpm to speed 51 mph. I believe it was a chaparral you can use that as a data point go to the website the show fuel burn at different rpm's. yours should definelty be better as your boat is smaller

 

[Rogerdog23]

muc i sent you the serial number on pm.

Long shot but could a bad gimbal bearing cause significant performance loss / excessive fuel burn?

Yes I was expecting a lot more performance than I’m getting. Doing 39 mph where I used to get 41 with the old 350 mag. And also burning about 25% more fuel. I don’t expect to see 51 mph but was thinking 45’ish when I repowered.

 

[muc]

ECM 555
Gen 2 Cool Fuel
10 pin connector
Mechanical Throttle and Shift
Closed Cooled Engine Block & Exhaust Manifolds
SmartCraft Ready
Engine Guardian
Runs on 87 Octane Fuel

For a bad gimbal bearing to do this, it would be making so much noise you couldn't ignore it.
Trim faults with this ECM won't engage guardian.
Guessing that a 14ga solid red wire would be for the MerCathode.

Hate to say this but it would probably be best not run this too much until it's fixed.

Maybe time to be a bit of a "squeaky wheel" at the dealership that installed this?

 

[Rogerdog23]

Appreciate it Muc. Not positive on the wire being solid red but it was red. Gimbal is making some noise and will need to be dealt with but is far from an egregious noise. Ugh.

Obviously you can’t diagnose via the internet but any hunches on what this could be given the trim sensor is the only fault I’m seeing? It sounds like you think I could do some damage if I keep running it so was just curious. Ever see anything like this on a brand new engine? Am I nuts to think that I should go faster and burn equal or less fuel instead of 25 percent more? Should I just head to the bar and cry?! Dealer is saying next week but said the same thing a week ago...they are just slammed.

Appreciate you taking the time to look up the ECM and offer your thoughts. Very kind.