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skyskier

Trouble shooters welcome.............

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skyskier

The boat is a 2005 Centurion with the EFI MAG 350 Mercruiser. 600 hours. It sat unused for two years with approx. 20 gal of Sta-bil treated gas in the tank. I did not drain the tank. I changed fluids and filled the gas tank and used it for wake boarding/surfing for a few hours without any trouble. I tried to use the boat a few weeks later and the gremlins came to visit.

Is it a fuel delivery problem?

1) First sign of trouble.....rider falls, pull the throttle back, engine stumbles and dies. Starts right up again and runs great until I pull the throttle back quickly and it stumbles and dies again. Changed fuel/water separator. That has fixed the problem when this boat has done this in the past. (says previous owner) Made no difference this time.

2) Drained every drop of old gas from the tank.....added 20 gal fresh fuel and a can of injector cleaner. No improvement. However, now the boat accelerates to top speed and then bogs out and dies after 15 seconds or so. If I throttle back slowly when the bogging down starts, the engine returns to a smooth idle. Next move is to replace the in line fuel filter and check the pressure in the fuel line. Picking up a fuel pressure gauge today.

Is it an electrical problem?

1) One multiple function gauge in the dash does not work at all. I noticed perfect pass cuts out when I turn on the sound system. The dash lights dance to the music. The sound system is a modest 500 watts or so. I replaced the two batteries with new fully charged batteries and checked all large cable connections. No difference at all.

2) Pulled the alternator and had it checked by a rebuild shop. They said the 70 amp alternator was only putting out 25 amps, but was functioning. I have a new alternator on the way.

If the problem still exists after I install the new alternator and in line fuel filter......and the fuel pressure tests ok......I am going to be at a loss for what to try next. Ok, maybe get under the dash and clean up all wiring connections.....then I will truly not know what to try next. Maybe buy a Malibu. I dunno. Your thoughts are appreciated.

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Falko

Your injectors are sticking. They are gummed up and when you back off quickly, they are still dumping fuel and you're drowning the spark. Run some of that injector treatment for a while and it might clear up.

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Vtxdave

Don't check just fuel pressure but volume fuel volume also. With the engine running you should be able to hit the relief on the side of the fuel pressure gauge and the engine not stumble or run rough and a steady stream of fuel should come out of the side port of the gauge. If it dosent and starts to run bad then you have the problem. I have seen where fuel pressure be is spec and volume be low and cause weird problems.

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REW

Check your fuel filter and then check the inlet of the fuel pump the screens on the inlets get gunked up as well.

Your electrical issues are going to take a bit longer to find. You are off to a good start with new batteries and all major connections. Now head for the smaller connections. There is a grounding bar under the helm, check all connections there and check for corrosion. You can fix a lot of these gremlins by unplugging the connectors and cleaning the connections then reconnecting. Contact cleaner is available in most auto stores, it comes in a spray can be careful using it around the interior materials and make sure your eyes are covered.

Edited by REW

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justgary

So if you slowly back of the throttle, it doesn't stumble? Is hard deceleration the *only* time it stumbles?

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skyskier

Yes, hard deceleration was the only time it stumbled at first. That is how this whole thing started. Now the engine runs great when I punch the throttle, but soon bogs down until I back off the throttle and then runs fine again. I swear this is going to be a fuel problem ALONG WITH an electrical problem. Gremlins seldom travel alone. I am headed to my shop tonight with a new alternator and a positive attitude.

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Vtxdave

Keep us updated. I'm interested in what you find. Did you get a fuel pressure tester by chance?

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skyskier

No fuel pressure gauge yet. Ran out of time today. I am picking one up tomorrow. Definitely will do an update. Thanks for all of the help so far!

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Rznhales

Unfortunately our Centurions are notorious for light gauge grounding wire in those years. The issue of gauges and stereo could be just that if the new alternator doesn't fix it. If I'm running the stereo and ballast pumps let's say and then hit the docking lights - mine goes nuts as well. It can't handle the amp draw. Head over the Centurioncrew.com if you need further help. Good group of peeps over there as well.

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REW

Unfortunately our Centurions are notorious for light gauge grounding wire in those years. The issue of gauges and stereo could be just that if the new alternator doesn't fix it. If I'm running the stereo and ballast pumps let's say and then hit the docking lights - mine goes nuts as well. It can't handle the amp draw. Head over the Centurioncrew.com if you need further help. Good group of peeps over there as well.

Are you talking about the grounding wire from the battery to the grounging bar or thr individual component grounds?

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Rznhales

Unfortunately it could be both. Have/did you have any issues with low voltage alarms going off?

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scottnance

Check your IAC may be sticking or dirty causing your decel stalling

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nyryan2001

Fuel injectors at 600hrs. they can be cleaned and recertified at a shop in Richmond.

You can try a super concentrated dose of a high quality injector cleaner through you gas first... Like Lucas. I would go x2 to x3 the regular dose... Or a full bottle of it on a 1/8 tank.

Centurion ground. Yes notorious. Find the ground where it terminates at the engine block. It is attached over the block's paint?

I've got a buddy who had to take a wire brush to remove the paint at the ground point due to engine noise and all sorts of trouble.

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skyskier

Two new batteries

new alternator

new gas

injector cleaner

fuel/water separator filter

fuel pressure gauge shows 20-30 lbs pressure and a steady stream from the relief port

cleaned gunked up spark arrester/air filter and throttle body. Sooooo much gunk! No way the butterfly valve was able to close all the way. No doubt this was the no idle problem.

After all of this the engine would barely run. The more throttle I gave it the worse it ran. Out of desperation I tried another new fuel/water separator filter and ran a fuel line to a remote gas can. Instant success! Then I connected the fuel line to the boat gas tank and took the boat out for a test drive. It soon started missing and barely ran again. While checking my work at the throttle body I disconnected the throttle position sensor and the engine was still misfiring, but with a different rhythm. Still no power. Then I plugged the TPS back in and the motor started purring like a kitten. Plenty of power and does not skip a beat.

I suspect there was air in the fuel system from the filter change. Maybe it was just coincidence that it cleared just as I was messing with the TPS, but re connecting the TPS made an instant difference.

So, in the end I don't know what was wrong overall. The dash lights still dance to the music, but everything electrical and mechanical works as it should. The engine stumbling when pulled into neutral is gone and I have my sanity back. The most important lesson learned is clean the air filter and throttle body now and then. I have a Malibu 247 that stumbles when pulled into neutral. I can't wait to get in there and clean that throttle body! Thanks to the crew for all of your help!

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skyskier

Oh, I forgot about this one. I cleaned all of the vinyl, including the sun pad, with water and Dawn dish washing soap. Upon fire up the serpentine belt spun on the crank shaft pulley and burned through. Apparently the soap found its way to the belt and pulleys. Maybe the belt was a little loose.....maybe not. I dunno. The message here is don't do that.

I saw this as a great time to replace the impeller while I was in there. You do not know joy and pure delight until you have replaced the impeller on a Mercruiser Black Scorpion. The raw water pump is under the engine on the port side. The pump has to be completely removed and disassembled to get to the impeller. This boat has hard tanks in the lockers. The port tank had to be removed. SO MUCH FUN!!!

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Bozboat

Fuel pressure at 20 pounds?? What is the fuel pressure spec for your boat? Low fuel pressure would cause the stumble and bog down.

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skyskier

I was thinking it should be 60 or so, but the local mechanic said 20 to 30 was about right.

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23LSVOwner

I think you need 58 PSI minimum.

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JeffK

EDIT: I see that you solved the fuel issue. If it comes back, this might help.

We had a go-fast boat in one time that would run fine until you pushed it hard, it would struggle, almost die out, then be fine again at lower speeds/loads. We finally pulled all of the lines form the tank to the engine. Turns out there was a ball of what I could only describe as plumber's tape in the elbow coming out of the tank. When there was a need for max fuel flow,. it would get sucked into the elbow and restrict fuel flow.

I would suggest pulling all the fuel lines, make sure you don't have any obstructions or gumming up in there and have another go at it. I would take an air hose at low pressure and try to blow them all out.

And I agree, 20 psi seems very low to me. 48-60 IIRC

Edited by JeffK

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RTS

My tank had a 'sock' looking thing on the fuel pickup inside the tank. Is that clogged up?

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skyskier

Well, I don't think anything is clogged up. If it is, it is not causing a problem at the moment. The boat is running like new!

Here is a story I will call "more fun with the yellow boat." I rent out ski boats on Lake Anna. This yellow Centurion is part of the rental fleet. Less than an hour after I got the boat running right, someone asked if it was available to rent for the day. I got it all cleaned up and delivered it within an hour. Two hours later I got a call from the renter saying he ran over the ski line. Well, when this dude runs over a ski line he is totally not jackin' around. He destroyed a 105.00 12" Masterline handle and 4 ft braided line, a 59.00 coated spectra line, and bent all four blades on the prop as well. After a couple of hours of him cutting the rope away from the prop, he decided to drive the boat the three miles to the ramp to meet me with the trailer. The boat had to be shaking like an out of balance washing machine, but he plowed forward anyway. I put on a spare prop and hit the lake for a test run. Once again, the boat purrs like a kitten. Total damage, not including my labor, 660.00. Insurance deductible, 600.00. I feel so sorry for this guy! He was just a grampa shelling out the big bucks to take his grand kids out on the lake to have some fun. Sadly, it bit him in the butt......and my work with the Centurion is not quite done. Again.

Btw, did I mention the blown out trailer tire on the way home from the ramp? That was truly magical!

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