Lack of power - 2003 Sundancer 280 w/ twin 4.3L

DMarcel

Member
Jul 13, 2011
74
Long Island NY
Boat Info
2003 Sundancer 280
Engines
twin MCM4.3L MPI V6 220 HP
Just bought the boat, ran great at sea trial. Left boat in water for 3 wks and it had poor power, high gas consumption. Changed gas filters, changed oil & filters, changed starbard cap & rotor, starboard engine running great!
Found broken screw in port distributor, changed distributor and all plugs. Starboard still running great, port engine running much better, but not as well as starboard. port engine not in sync w/ starboard, running about 800rpm behind starboard at 3800 to 4600 respectively. at idle 800 to 1100.

The engines are 4.3L v6 fuel injected.

Does anyone have any ideas? My next plan of attack is to put Chevron fuel injector additive in the fuel, followed by new ignition wires. There are only 180 hrs on the engines.
 
Have you checked the compression on the motor. I would do that while you are messing with everything else. Did the PO have any issues that they mentioned?
 
You said you left the boat in the water for three weeks and I see you are in NY. Do you have bottom paint? If so, is it in good shape? It sounds like you have growth on the bottom of your boat, slowing you down and ruining your performance and fuel consumption.

Make sure your engines stay synced, otherwise one is fighting the other. Use the sync gauge, don't just keep the throttles together...
 
The bottom was painted prior to putting it in the water. There are no barnicles or grass on the bottom. When the sync meter shows both in sync, the port engine is much slower than the starboard. I'm assuming the sync meter is based on gas consumption??? Since the tacs are not the same. When the tacs match, the sync meter shows to the right indicating too much port engine.
 
This time of year around these parts... if I left my boat in the water for 3 weeks and didn't move it, it would also have no power... The growth on props/shafts/bottom (even with paint) is obscene this year. Before our big trip up to the NE, I had the boat dived on 2 weeks before we left... I had to have it dived on the first day out because I could only cruise at 1900 RPMs (normally cruise at 2100).

Before I would start messing around with the engine, I would have the boat bottom and gear looked at and cleaned.
 
When did your boat go in? Double check your outdrives for growth. It doesn’t take much to slow the boat down. I keep mine a little further east and already had it pulled, outdrives scrapped, and hull power washed. It was a night and day difference in performance. I don’t think the sync has anything to do with fuel consumption. It should be based off of RPM.
 
Like I said, there is no growth. I'm under the boat once a week. It is a problem with the port engine or else it's the guages, but I don't think so.
 
You can try to sync the engines by ear and see how off your gauges are. When in sync they should have a steady hum rather then a droning sound. Also full throttle should give you a GPS speed between 40 and 44 mph. If all else fails then you might want to have a Merc mechanic plug into the diagnostic port to check for trouble codes.
 
My speed is no where near 40mph. I will add Chevron injector cleaner to the gas and if that doesn't work, I'll have a mercruiser mechanic do the diagnostic. I didn't realize that they had the diognostic port.

Thanks!
 
The engines seem to have responded and appear to be in sync, but the tacs are still off. Does anyone know how I can set up independent tacs?
 
I'm pretty sure your engines are the same as mine although mine are a year newer and have the Smart Craft Setup. Therefore, on the front of the engine by the thermostat housing (maybe a little to the right) you should see a few wires. There should be a black wire and another wire (don't remember the color) with bullet end connectors. They should be tagged as Tach. Since you don't have the Smart Craft Setup (at least I don't think so) your tachs may be plugged in there.
 

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