Port Engine looses RPM's on extended crusing runs

O

Off Mic

New Member
Apr 3, 2019
9
New Buffalo MI
Boat Info
2002 380 Sea Ray Sundancer
Engines
8.1 Horizons
2002 Sea Ray 380 w/8.1 Horizons. W/Gen 2 cool fuel module.
My Port engine won't maintain cruising RPM (3,200-3,400 RPM) after about 2-2.5 hours of cruising. It acts like it wants to stall and sputters and drops to idle speed (900 rpm) but never actually stalls. If I shut engine down for 5-10 min it will start fine and runs fine for another 1/2 hour or so. It has happened 4 times in the past 2 years and only on long cruising runs. I have changed water sep filters multiple times and last gas sample showed no signs of moisture in fuel.

I'm starting to think it is some kind of heat build up issue, since it always happens about 2+ hours in to a long run. (All engine temp gages on the dash read normal)
Last week I got almost to 3 hours by varying my RPM every half hour or so 3,600, then down to 3,200 then 3,800 back to 3,000 etc, and I also ran my blower the entire time. Also Fuel gages all seem to be between 1/2 to 1/4 when it happens. Fuel Pick up line??? Mercruiser support says to do a fuel pressure test when it happens. But ,well, how do I do that when I never know when it is going to happen??? ;-)

My Mechanic is backlogged on work but I'm trying to get as much info I can to help diagnose.
Any thoughts GREATLY appreciated!
 
It’s sounds to me like it’s a loss of fuel supply. I agree with a FP test. Get a gauge set up and when it fails, hook up the gauge, make sure you have no leaks, and open the throttle.
 
Agree, it actually does act like some kind of fuel starvation, but its a tricky ghost to capture when you never know when it will happen.
 
Had same issue with my stbd engine. Chased it for 2 seasons. Changed plugs, no help - changed plug wires, went away. Had already did the FP testing and ruled out the paint issue by having injectors professionally cleaned, filters changed and fuel pumps bench tested.
 
Korkie said:
Had same issue with my stbd engine. Chased it for 2 seasons. Changed plugs, no help - changed plug wires, went away. Had already did the FP testing and ruled out the paint issue by having injectors professionally cleaned, filters changed and fuel pumps bench tested.
Click to expand...
Korkie said:
Had same issue with my stbd engine. Chased it for 2 seasons. Changed plugs, no help - changed plug wires, went away. Had already did the FP testing and ruled out the paint issue by having injectors professionally cleaned, filters changed and fuel pumps bench tested.
Click to expand...
 
Ah Ha! We did change plugs, but wires seemed fine so did not change them. Will add that to list of things to consider! THanks much
 
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