Engine problem - thoughts or opinions please

[Glen S]

Ok, so this is what happened (trying to add all possible useful/ pertinent info)
Tuesday – picked up about 40 gal fuel and then back to our slip (1/2 tanks)
Saturday – 10 mile run down St Clair River to the town of St Clair
Sunday – picked up about 100 gal fuel (3/4 tanks)
Idled and maneuvered waiting for the bridge to open to get back onto the St Clair River.
On the river ran at about 2000 RPM near the shore for about 5 mins waiting for a freighter to clear. All gauges reading normal. Driving into a very strong winds and a very fast running current. Opened up to 3200 RPM.
A couple of mins later port engine drops to idle (throttles do nothing) and starboard engine drops to about 2700 RPM and does not seem to want to throttle up past this.
Turn around back to the harbor. Waiting for the bridge to open the port engine stalls.
Get to the fuel dock and shut down.
Check the ER – nothing unusual to see – all looks in order.
Start engines- both start and seem to idle fine although engine sync gauge is very slightly off. Both seem to rev freely (no load). Engines running smooth – no strange noises etc.
Move the boat to a transient slip – both engines running – port engine even seems to respond to throttle as we maneuver. Sync gauge reading normal again.
With the high winds and very strong current did not think it wise to try to limp home on one engine that seemed to be suspect and one not keen on running.

Boat is a 1997 400 DA
Engines are Merc 7.4 MPI’s = about 700 hrs.
Engines have run great all season. Have all new spin on fuel / water separator filters this spring. So, have called a local recommended marine mechanic – but being Sunday – hoping to hear from him tomorrow. Several boats from our home marina were at St Clair harbor – got a ride back to our marina.
Not great having my boat left in another country but………

So, my questions are:

Any thoughts on what would cause the engine running at 3200 RPM to drop to idle without touching the throttles and render the throttle useless? The only 2 possibilities that occur to me are electronics or fuel restriction?

Second – would dropping one engine rapidly to idle cause the other to loose RPM due to load? Several opinions on the dock thought so – consensus is that the starboard engine is fine. Hmmmm….

Thoughts? :huh:

 

[mainstream]

Sounds like guardian mode low oil or transmission
fluid if you have v drives

 

[cod]

Water in fuel? Do you have separate fuel tanks?

 

[Great lakes pirate]

Maybe a fouled prop?

 

[Glen S]

Sounds like guardian mode low oil or transmission
fluid if you have v drives

Oil levels in the egines are fine. I did not think to check the trans - which are the V drives.

 

[Glen S]

Water in fuel? Do you have separate fuel tanks?

Yes - seperate fuel tanks.
It was suggested (back at my marina) to change fuel / water filters and add the water treatment to the fuel.

Thanks,

 

[Glen S]

Maybe a fouled prop?

I have never had the misfortune of a fouled or wrapped prop but I thought if it were fouled enough to bring an engine from 3200 to idle that it would shut it down completely. This sat at idle for about 5 mins before stalling. It also ran in gear leaving the fuel dock. However, I will add it to the list to discuss with the mechanic.
Thanks.

 

[cod]

Remove the existing water separator and empty it into a glass jar. You will be able to see the fuel and water separate after letting it sit for a while. Water and fuel will stay separated at idle but as you go on plane and the boat bounces around a bit, fuel and water will start to mix.

Yes - seperate fuel tanks.
It was suggested (back at my marina) to change fuel / water filters and add the water treatment to the fuel.

Thanks,

 

[mysticowner]

If it were water in the gas or a fouled prop I agree it would shut the engine down. Seems
electronic if it sat there and idled in gear.

You should have felt the prop out of balance if it caught something wouldn't you?

 

[Glen S]

Since my usual mechanic is in Canada it is difficult for him to get across to the states to work on the boat with all his tools - need work permits etc to get across boarder.
So I spoke with the local recommended mechanic this morning. He believes it is an electrical issue that put the engine into gaurdian mode. He is heading down there this afternoon to check it out. He has the Mercruiser diagnostics on his lap-top so should be able to see the faults recorded on the onboard computer. He is also going to spin off one of the fuel filters and drain / check the contents. However, he doubts it is fuel related since it would usually result in a rough idle etc. Keeping my fingers crossed it is a simple fix - supposed to be on vacation on the boat starting tomorrow.