Cummins 330's - 1998 Won't hit full RPM's

[skolbe]

So my dock neighbor bought a 1998 - 4100 express cruiser Maxum last fall. He has had nothing but problems getting it on plane. He has put $10k into it and that includes props redone, bottom paint, new injectors, and the boat won't get past 2600 RPM's. He has replaced the fuel and included additives. He has fresh fuel. Had the air systems all cleaned out. I am not a diesel guy. Just curious if this is normal. Boat only had 450 hours on it. The thing is both motors have issues getting past 2600 rpm's but the bottom is clean. The boat won't plane out. It has been intermittent and it did at one point get on plane. The Cummins mechanics just keep wanting to replace parts. They are suggesting a new head gasket now. He is frustrated any ideas?

 

[fwebster]

What happens when the throttles are advanced to WOT with the boat in neutral?......There is a spec for no load high idle and it if hits the spec, then you know the engine is right. This is one of those things where you can't just throw money at it....there has to be some common sense rationale to what you are doing. For example, it both engines are peak out at about the same rpm, and that is 200 rpm off WOT spec, even though he had "the props redone" I have to wonder if the pitch is right for the hull and the load on the boat. The 330hp 6BTA cummins isn't a power house in the first place and are relatively low torque motors, so the load on the boat, as well as anything creating drag is going to be felt in engine performance big time.

I know how Sea Ray tweaks props to their boats and there just aren't any 200 rpm mistakes after about 1995 or so, unless Bertha is a 400 pounder, but I have no clue about Maxxums or even if there is reasonable assurance that the boat was ever right when it left the factory.

 

[Gofirstclass]

Just out of curiosity, does he know what the WOT rpm's should be? My Cats' WOT rpm is at 2150. Just asking.

Did he check his throttle linkages? Doubtful that both would be bad, but I'd check to make sure they are adjusted properly. They could both have been improperly adjusted by the same tech who didn't know what he was doing. It almost sounds like the engines aren't able to go to WOT due to that linkage.

It's not a problem with either engine or either drive train since both drive trains are doing it.

 

[trit21]

I was thinking the same thing, check no load WOT in the slip and record RPM of each engine. If not at spec then check linkage for throttle and verify it is open fully. Easy easy checks since we are assuming bottom is clean.

 

[skolbe]

They hit 3000 in neutral. Both engines. The tech is saying it is the running gear/props. The bottom is clean.

 

[fwebster]

Is this the same Cummins guy who wants to change the head gaskets?

Have him take 1.5 inches of pitch out of his props and go have fun.............that is just a quick comment. He should verify that the bottom is clean of everything including the slime/algae then talk to a prop professional with real experience...not just a blacksmith with a PropScan device......and ask them to figure what he needs based on his performance to date, the hull, weight/load, etc. MAking the prop guy determine what needs to be done hooks him up with the responsibility to tweak the props if he is a little off the first or second time.

 

[trit21]

First thing I would do is get rid of that mechanic , sounds like he sold your friend a lot of stuff he didn't need like injectors. I have heard that a couple of times already about cummins techs down here but apparently is everywhere. After that, sounds like Frank is dead on. Engines are turning up to 3000 , rate at 2800 (need to verify that btw), so engines are not the problem. Boat is overloaded and props need adjusting so they run at minimum 2800 at full load although a little higher would be better, 2850 -2875.

 

[skolbe]

So the latest is really unexpected. Friend called Cummins and said that he wasn't going to put any more money he was already up to $5k with Cummins. They ended up wiping his bill clean and starting over with a new technician. So he is encouraged. He is not even having to pay for the parts and service from before. They said it was their fault for misdiagnosing the problem. I have to say that is impressive. I know it is not fixed.

 

[trit21]

Have him go to www.boatdiesel.com and ask the experts there, they will probably come up with the same diagnosis as Frank has, props need to be redone so the boat will reach ++ rated RPM fully loaded. Tony Athens and sbmar.com (his site) has an enormous amount of information on his site. Just saying.

 

[skolbe]

Thanks and I will let you know what they end up ultimately deciding.

 

[skolbe]

Ended up being both fuel pumps. They were replaced and now planes out fine. They didn't charge him for the misdiagnosed work.