6BTA troubles

[Jwstyn]

I have a pair of Cummins Turbo Diesels (6BTA 5.9-M3) with a hard-to-find problem https://mechanicfaq.com/turbos-for-5-9-cummins/. Advice appreciated.

Everything was fine in the morning, cruising at 2,500rpm/25kts. Tied up for 2 hours over lunchtime. On return trip both engines refused to rev past 1,500rpm/9kts. Would go to 1,500 at one third throttle position, but moving throttle after that would not result in any more revs or speed.

Things checked so far:

- I did not fuel up that day. Last refuel was followed by several hours of successful boating so bad fuel is unlikely.

- No noticeable smoke. No weird vibrations, noises or smells.

- We have checked fuel screen and filters, which are OK and correctly specc´d

- Checked throttle mechanisms, which are OK

- Engines are turbo-charged and we did have issues with one of the turbos not spooling up so we have overhauled both turbos. No improvement.

 

[Higgo]

I have the same engines and would firstly be checking your fuel filters as you potentially got a bad batch of fuel (either dirty or contaminated with water). I'd imagine you have an on-engine screw on filter "FF5285" (Fleetguard) and a separate primary Filter (possibly Racor). How long has it been since the filters have been changed? If the sight glass on the primary filter is reasonably clear, unscrew the onboard engine fuel filter (not oil filter (LF....) and see if the fuel in the top of the filter is also reasonably clear. If so, put it back and tighten. You'll need to then reprime the hand pump plunger on the side of the injection pump till it become firm to repressurize the system. If it looks dirty, change out the on engine filter (fill with diesel first). If it is water contaminated, changing it anyway might not be a bad idea.

To check whether it is a water contamination issue, you would need to isolate your existing tank supply. I'd get 2 plastic 20L drums of clean fuel and 2 lengths of fuel hose, cut/punch out a hole in screw on cap for the hose to fit tightly and connect to the primary filter inlet spigot. Start engines and take the boat for a run and see if the problem is solved.

If not, it may be the aftercooler cores impeding airflow from the turbos. So how long has it been since the cores were removed and cleaned. One may be cleaner than the other but you typically need both to get sufficient power to get you over the plane hump. Boost pressure is the typical indicator of air thru put, but you have to get to cruise revs to get an indication that all is good.

Clean fuel, a clean bum and clean cores are all needed for optimum performance. Hope this helps. Good luck with it.

Cheers

 

[jrudge]

I dont know your engines - but are they electronic?

Electronic systems tend to match RPM - so if one has a problem the other one comes down to the same RPM regardless. As such the issue could well be on one engine only with the electronics then making it seem like both.

There was a post on here a while ago that was similar and the cause was prop slip as they needed re bushing.

Also if electronic have you re calibrated the throttles. No reasons why they should reset, but you never know.

 

[mcanderson]

Are you running outdrives? If so I had a similar problem and it was, indeed, a slipping prop.

 

[burgundyben]

- Checked throttle mechanisms, which are OK

With the gearbox in neutral what max revs do you get?

Have you disconnected the throttle cable and checked you can get max revs at WOT?

Sure there is nothing round the props?

Which CPL are they?

 

[jrudge]

To check whether it is a water contamination issue, you would need to isolate your existing tank supply. I'd get 2 plastic 20L drums of clean fuel and 2 lengths of fuel hose, cut/punch out a hole in screw on cap for the hose to fit tightly and connect to the primary filter inlet spigot. Start engines and take the boat for a run and see if the problem is solved.


Cheers

I think you will find you run out of fuel in minutes or less!

I just did something similar on a Williams rib. I was aware that fuel recirculated via the return - but had no idea just how much!

I had a 20 litre can. It had about 15 litres in it. I ran out of fuel idling in the marina after about 150 metres. Reconnected tank and returned to the boat.

 

[benjenbav]

Just about the only issue I had with similar engines had similar symptoms and was very straightforward to fix: jubilee clip on turbo-hose failed and was fixed by a simple replacement. Worth checking if not already done.

 

[NBs]

Hi

I recommend you to inquire about this seaboard forum, you will definitely be assured of Tony's guru Cummins marine engines +35 years.

https://www.sbmar.com/community/

NBs

 

[Bouba]

I dont know your engines - but are they electronic?

Electronic systems tend to match RPM - so if one has a problem the other one comes down to the same RPM regardless. As such the issue could well be on one engine only with the electronics then making it seem like both.

There was a post on here a while ago that was similar and the cause was prop slip as they needed re bushing.

Also if electronic have you re calibrated the throttles. No reasons why they should reset, but you never know.

I was also wondering that and thought that something could be around the prop or props, like rope or a net. If the engines are not synced electronically then I would be looking for everything that the engines share in common starting with the diesel tank, airlock or sludge etc. Then if the engines share anything after all the way to the props.

 

[ARE]

I have a pair of Cummins Turbo Diesels (6BTA 5.9-M3) with a hard-to-find problem. Advice appreciated.

Everything was fine in the morning, cruising at 2,500rpm/25kts. Tied up for 2 hours over lunchtime. On return trip both engines refused to rev past 1,500rpm/9kts. Would go to 1,500 at one third throttle position, but moving throttle after that would not result in any more revs or speed.

Things checked so far:

- I did not fuel up that day. Last refuel was followed by several hours of successful boating so bad fuel is

unlikely.

- No noticeable smoke. No weird vibrations, noises or smells.

- We have checked fuel screen and filters, which are OK and correctly specc´d

- Checked throttle mechanisms, which are OK

- Engines are turbo-charged and we did have issues with one of the turbos not spooling up so we have overhauled both turbos. No improvement.

It sounds like a fuel supply issue as there are only a few things that would effect both engines. These are all mechanical engines, so it’s unlikely a failure on both engines at the same time.

 

[superheat6k]

My bet here would be fuel, but worthwhile seeking our Latestarter of this parish. He is the forum guru on Cummins.

BTW I have the manuals for the Cummins, with an excellent service manual for off road equipment using the 6BT range.

 

[NBs]

My bet here would be fuel, but worthwhile seeking our Latestarter of this parish. He is the forum guru on Cummins.

BTW I have the manuals for the Cummins, with an excellent service manual for off road equipment using the 6BT range.

With this Cummins own service link, you can register your own engine and get all the information on your engine. Trouble shooting, work shop, all spare parts, etc. Great awesome service at no cost.

https://quickserve.cummins.com/info/index.html

NBs

 

[Higgo]

Jwstyn, I've sent you a PM. Check the top banner for "Notifications". Cheers