Engine won't go over 3,200 rpm under load

BostonSearay

New Member
Jul 22, 2017
1
Boston, MA
Boat Info
320 Sundancer 320
Engines
350 Mercs
2005 SD 320. Merc 350mags. Last season after experiencing reduced RPM and vibration from my port engine (wouldn't go over 2,600rpm under load). Mechanic suggested a full tune up.
they replaced, spark plugs, cap and rotors, fuel filters, flame arrestor.
I ended up gaining about 200 rpm. I called him and he said that he couldn't think of anything else and that he would take a look during the off season.
Went to a different mechanic during the off season and he noticed a faulty distributor, which he replaced. We also replaced manifolds and risers. Took it out for the first time last week, and boat was overheating and alarm went off, due to low coolant. I added coolant and resumed my trip. Vibration is gone, however the Port engine won't rev over 3200 rpm and SB won't rev over 4200rpm. I called him and he advised that I disconnect the batteries in order to reset the Guardian safety, which most likely kicked in after the overheat incident. I was also advised by another mechanic to replace the anti-siphon valves and add fuel system cleaner in my fuel.
I noticed that there are no anti-siphon valves on the fuels tanks just a line going to the electric pumps, can it closer to the engine?
I am really frustrated with this problem. 400 hours on the engines and always professionally serviced and maintained.
Another issue is that all mechanics are at least 3 weeks out. Season is too short in New England.
Any advice would be greatly appreciated.
 
I had a similar issue with my 310 a couple of years ago. One engine was running rough and not making rpm. Turned out to be two bad fuel injectors. That wouldn't explain low coolant and overheating issues, though. And odd that the low rpm condition that affected one engine last season is now affecting both.

Many Sea Ray's don't have anti-siphon valves, as they use electric solenoid valves.

I'd also make sure that engine fuel filters are replaced as well as remote water separating fuel filters, if you have those. Also, not sure if this applies to your boat or about which engines were affected, but Mercruiser had issues with some Cool Fuel 3 systems where internally painted parts in the fuel pump were shedding paint chips, I believe, and they were contaminating the fuel rails and injectors.
 
Good advice above. The engine fuel filter referenced is in the fuel pressure regulator on the cool fuel assembly. I found mine nearly clogged and cleaned them.

IMG_0459.jpg IMG_0461.jpg IMG_0456_1024.jpg IMG_0462_1024.jpg IMG_0458.jpg
 
Good advice above. The engine fuel filter referenced is in the fuel pressure regulator on the cool fuel assembly. I found mine nearly clogged and cleaned them.

View attachment 70577 View attachment 70578 View attachment 70579 View attachment 70580 View attachment 70581

Awesome photos! Exactly which filter I was thinking of! But, not sure if Cool Fuel 3 has the same fuel pressure regulator and filter. I believe that the issue Merc was having with paint shedding was affecting rails and injectors, but that filter in the regulator would have caught them. But, indeed, this issue sounds like a fuel delivery issue.
 

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