Any ideas what is causing my 350 mag MPI to bog down at 2800 rpm?-gctid817159

[BoatingBC!]

Hello everyone. I've got a 2000 350 Mag MPI inboard on my 24' Ciera Classic which has been running great since last year's tuneup. I put about 70 hours total run time on the boat last summer, then winterized it.

I dropped it in the water in late June and it has been running like a top. Fluids are all topped up, I did an oil change at the end of last season. Trying to get out of the hole and up on plane, the engine begins to surge at 2800 rpm.

I changed out the fuel/water separator today with a new one and took it for a sea-trial, same result. No sign of any leaks in the fuel lines. I played around with the trim-tabs and once I got over the 2800 rpm and up on plane, I was able to cruise at 2900/3000 with no problem.

I'm wondering if I need to check the fuel pump and fuel pressure. I had new plugs put in at the beginning of last season ( again, about 70 hours on them).

Any advice is appreciated. Thanks!

[Timcup]

Do you have a fuel filter installed prior to the fuel water separator hat has not been changed? Perhaps before a fuel flow sensor?

Could be fuel pump. Restriction is more a likely culprit.

[BoatingBC!]

Hi Craig, no fuel filter installed prior to the water separator. I'll check the hoses from the tank. I thought the new fuel water separator install today would have fixed the problem....I'll have to check the fuel pump after I see if any of the fuel lines are kinked/restricted.

Thanks!

[TenMile]

I used to find on mine that once in a while I'd get a dirty injector. It would feel like the boat had less power to a certain range and would then all of a sudden feel like a turbo charger kicked in. Often it was the injector finally opening.

I found that doing the Sea Foam Shock Treatment worked very well to clean the injectors up. No harm in doing it. I'd take a 1 gallon fuel can of gas and add an entire container of Sea Foam. I rigged up a fuel line to the fuel pump and ran it into the can. With the engine already warm, start the boat running on the new fuel, and run the engine up to 2000 RPMs and let it run like that for about 5 minutes. The the engine sit for 30 minutes and then do the same process again -- run for 5, sit for 30. Then take the boat out for a good run afterwards. I found the process very successful at cleaning up any dirty injectors.

Note that if you do it on the hard, after the first 30 minute sit, when you start the engine again you'll experience a bunch of white smoke from the exhaust. That's the crap being burned off and is normal. It will clear in a few moments.

[aluxury1]

Is your fuel alcohol free? How old is it?

[BoatingBC!]

Thanks for all of the ideas and suggestions. After a new fuel/water separator, Sea Foam treatment, checking the hoses for leaks, I've checked the fuel psi in the rail and it is only at 25-28 at idle and 32 under load. When I add throttle to WOT, the pressure drops to about 24 psi. I've checked the manual and it seems to say I need around 42 psi ( only getting about 4000-4100 rpm at WOT as well, about 600-1000 under spec )

Has anybody had their fuel cooler ( Mercruiser KoolFuel) system replaced? It's in a crazy awkward spot, below the serpentine belt at the bottom of the engine. It houses one of the two likely culprits, either the boost pump, or a throttle sensor.

Of course, nobody sells just those items individually any longer, I've been told I need the entire 'kit'.

Anybody had this kit replaced before?

[Ruffryder]

Cool fuel GEN 2 should be on your boat.

43 PSI fuel pressure REGULATOR on the cool fuel body. There is a REGULATOR FILTER under the regulator... will need to check or replace.

[Ruffryder]

fuel pressure is good...30 PSI for your engine,

REGULATOR marking needs to be verified to see what you have, pink 30 PSI, blue 43PSI, Only small block scorpion is 43 PSI.

[Centerline2]

if the engine is running out of power and has a surge to it, its undoubtedly a fuel starvation issue...

[BoatingBC!]

Thanks for all of your ideas/suggestions everyone. An update. After enjoying most of the summer with my boat out of the water, it should be back to me tomorrow. I'm hoping the shop calls me in the morning. New Cool Fuel system ( what a headache...more about that later) New manifolds/elbows, risers as my boat is raw water cooled. Looking forward to see how the sea-trial goes tomorrow.

If anybody in Canada is looking to replace your CoolFuel system, a couple of things.....even a Merc Authorized Dealer has issues with head office not sending the pressure regulator with the new kit, which of course, is no longer available as individual parts, but an entire new kit at about $750 Canadian. Apparently there weren't any pressure regulators anywhere in Canada, one had to be flown from head office, then it was learned despite Mercruiser having my engine's serial number, they sent the wrong generation of Cool Fuel modules.

As for the raw water versus fresh water cooled debate, after spending $$$, I don't have the $$$ for a freshwater system right now. Has anybody rigged a freshwater fill-line on a 't' junction on their seawater intake hose? Just wondering if there is a way I can fresh water flush without having to remove the boat from the water. Despite living on an island, no good boat ramps to launch/load.

Thanks for any suggestions.

[TenMile]

Hi Mike,

Yes, I've done this before. There is a product that you can purchase in a kit, or make it yourself. Essentially 3 valves plumbed together -- better to use heavy duty bronze valves rather than plastic. One that stops the raw water in, one that stops the water flowing to the pump, and a valve with a garden hose fitting.

Use Salt-Away in the garden hose attachment. Close the raw water intake valve, open the garden hose / Salt-Away valve, start water flowing, start boat, flush system at idle until you see the soapy bubble appear in the water. Shut engine off. Open raw water valve, and close garden hose valve.

[builderdude]

Perko flush pro is an option, a few members have used it with no issues.

https://www.starmarinedepot.com/perk...iABEgJ70_D_BwE

[Ruffryder]

Mercruiser should have known GEN 2 cool fuel module on a 99 engine,

so were you able to get the right kind pressure regulator?

[iceman11]

Good luck with your sea trial, hope your problem is resolved. I'll be interested to hear what finally fixed the problem. I have a similar bogging down issue with a Mercruiser 5L MPI engine. One mechanic thinks the fuel injectors are plugged, and another one thinks I have a degraded valve seat that's leaking. I've lost most of the summer of boating too. So frustrating!

[Ruffryder]

Yup, when an EFI engine acts up, it can be a real PITA to diagnose even using a scanning tool!

Ice, you should have all your injectors cleaned PROFESSIONALLY... it is recommended to do them every 300-400 HRS or 3-4 YRS.

injectors clogged most likely, just because you have a GEN3 fuel module.

Start your engine, before she gets too hot, see if can touch each exhaust manifold port from the underside...clogged injector, non-firing hole won't be too warm.

Unplug the injector connector on your suspected hole, see if that will make any difference.

Now unplug the spark plug wire on that hole, pull the plug to inspect wet or dry.