Cummins QSB 5.9 lost power on plane and vibrates

[Luke Lapham]

Hey guys, new to the forum,   We recently just took our Tiara 3600 sovren to key west and back. Put about 4-500 miles on the boat and it’s powered 380 QSB cummins. while crying back through the inter coastal about 10 miles from home my starboard engine lost power and I brought the engines down to an idle. The engine never turned off, but now it vibrates the boat in neutral and has power loss.  The oil pressure was perfect and the heat was at 180-181 degrees when this happened.  there was no oil slick behind the boat and no smoke to speak of when this happened. The motor will start up but vibrates like it’s missing… I’m just hoping nothing catastrophic has happened.   let me know if anyone has seen this or what they think.  also I checked the valve train and it looks perfect, and the oil is exactly where I left it when I changed it last. 

Topic

[Rob Schepis]

Luke when you have time give this a thorough read:

Propellers Move Boats, Engines Just Turn Them

[Luke Lapham]

Propped correctly?

I guess I’m not understanding what you’re saying about the props.  I have opened the engine up to full RPM in the past to excerise it and clean any carbon build ups and it gets up to speed speed and full rpm without an issue.   so what is it that your meaning? boat weighs 20,000 lbs 36 Ft long and has twin cummins 380’s.  Again unless I’m the only one with that set up, I feel there would be other reported issues since the props are stock from the builder…

[willyok]

You are correct, on a properly loaded QSB this is not common. If you have never gone above 76-77% load you have no clue if you are propped correctly. Also the load percentage doesn’t mean a lot. Fuel burn GPH at specific RPM compared to Cummins specs, not Tiara is what is important. 

[Luke Lapham]

Head replacement

As far as replaceing the running engine, I was told to not mess with it per cummins and a cummins repair tech that came out to assist in figuring out the problem.

The boat is getting the same fuel economy as Tiara had on their performance sheet when it was manufactured. I have never ran the boat more than 76-77% load. Rpm’s are also the same on the performance spread sheet as well.

I watch the tiara forums and see the same boat with the same 5.9 with double the hours and no issues. I’ve never seen a valve break in this man or unless the engine got hot at some point in its life and got brittle and the king trip we put on it stressed it to its last life.

 

There are also no more new heads available for almost year per cummins, and funds to get one arnt available for me at this time.

 

I believe this is an isolated case on a bad cast of a valve as I have been in contact with multiple marine cummins techs at 1800 Cummins and they all confirmed that this is extremely rare. 

[willyok]

You got luck the valve didn’t let go completely and even luckier you have access to drop the oil pan in place for rod and piston replacement. 

 

I would say its an uncommon failure in vessels that are loaded and operated in accordance with Cummins publications. That being said,  I have seen this happen on two 480HP QSBs in Law enforcement/fire boats that are run WOT 99% of the time by non mechanical operators. 

I also saw it happen to a 425HP QSB in a private sportfish. This was caused by massive overloading/prop issue. 

After repairs, make sure you are propped correctly and your fuel consumption is at or below the curve. and since your doing the labor yourself, Id go ahead and replace the other head as well. 

[Luke Lapham]

Update to problem and being foxed

I’d thought I’d update the thread since no one got back to me.

 

it was NOT the Aftercooler and they are in Pristine condition. The cause of the failure was a broken valve. A piece broke off and then smacked the piston. No damage to the cylinder.  I removed the head and and have a OEM one here for replacement along with a new piston, rod and bearing for good measure.  Cummins has rarely seen this happen per them and it had nothing to do with maintenance.

I did the tare down the engine myself and am completing the repair. I hope this post can help someone out in the future.

 

[Luke Lapham]

Video of both engines running

Hero tried putting a video up but it is too large at 12 seconds…so I tried to trim it down. <br /><br />

anyway I have a called a tech to come out as I’ve gone through everything I can to figure it out.

[pwrobert]

Tony has a method to sort thru the issues.  With many people not able to fully explain or even know the names of their engine parts he has to go through the basics first to get at the possibilities.  If you want his help follow his requests.

However, on one of my 6BTA’s I had a similar situation a few years ago after they were first installed.  It turned out that the Gear to the fuel injector pump had loosened on the shaft and was then out of timing.  The tapered shaft has no key and is totally a friction fit.  There is an alignment tool required on the 5.9L engines to line up the cam  and fuel injector pump then the shaft and gears must be cleaned and degreased and re tightened with somethinig to help lock the shaft/nut.  I don’t remember the product but it was someting like a super Lock-tite for the purppose.

May or may not be your problem.  Tony can work you through the process – if you let him.

[Luke Lapham]

Cummins QSB

As far as the Aftercoolers ..The boat was purchased 1 year ago. I contacted the mechanic that had the service done on and was informed of the service to them at time of purchase. Which was listed on the work order. We use the boat non stop and have put 140 hours on it in 11 months. We just got done putting 50 hours running to key west and back with no issues until 10 miles from home when it lost power. <br /><br />

I monitor the oil pressure and the engine temp and both were perfect. 180 temp and 50psi on oil pressure. The engines starts and pushes water thru the exhaust like normal, but there seems to be something off.

 

 

the issue that the boat is having is not aftercooler related as shown in the pictures the cooler is clear and no signs of water intrusion or misting.

Ill post pictures of the cores from the intake to the turbo. I am very mechanical and build gasoline marine engines. I just am trying to diagnose if this is a bad injector problem.

 

 

[Tony Athens]

Last chance if you want me to keep trying to  sort thru this remotely–Otherwise you need a in-person tech

Did you “see” aftercoolers on the bench with the cores out?

Pictures as requested

[Luke Lapham]

Cummins QSB

Port – 46416396, Stbd – 46416333<br /><br />

my SMX guage shows 590-600 Rpm nothing different in it to show. The Aftercoolers were serviced 2020 and boiled and pressure tested and again in feb 2022 both pressure tested.

 

the engine vibrates in neutral and appears to be not firing on a cylinder. It doesn’t sound as normal as the other engine.  There is no knocking noise. I’m wondering if this could be a bad injector. That just locked up closed while cruising.

 

 

 

[Tony Athens]

I’m still waiting for all I asked.. My request was clear

Vibration   or missing  in neutral or in gear?  RPM’s during this?

Add serial numbers  & the history of aftercooler maintenance.

Add good picture of your instruments turned on, engine running

[Luke Lapham]

Cummins qsb 5.9

740 hours on each engine.

no codesIt runs and idles but is vibrating like it’s missing and won’t get full rpm and can’t get boat on plane.

 

no codes, oil pressure and engine temp were perfect.

 

no oil or smoke from exhaust 

[Tony Athens]

 

Define “lost power”– be verbose with all details before & after

Alarm codes? 

Looked at the running gear? 

single or twins?   

total engine hours?

Post Good pictures of the overall installation

[Author]

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