Rough Idle on Caterpillar 3208 Suggestions?

[whatever]

We have 2 Caterpillar 3208 diesel engines aboard our Trawler. Started out on the port now the starboard is doing it also. Rough idle when starting, until we get them up to 1000 rpms. Will not run normal until we get it to 1000rpms. Raycors have been removed and cleaned, new filters installed. Any other ideas that a learn as I go Captain can check before we throw up our hands and get a diesel mechanic involved? Appreciate any suggestions, Thanks!!!

[River Cruiser]

Have you changed the secondary fuel filters mounted on the engines? If not that would be my next move.


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[whatever]

Yep, River Cruiser , done and changed to a more expensive filter just to see. No change to rough idle. Thanks for your suggestion though.

[DeepFrz]

What were the filters like when you changed them? Any water in the bowls? Any smoke that wasn't coming out of your exhaust before this started? After engine warms up does it run well at idle? How many hours on the engines? Is it time for injector cleaning and testing?

[Sailmonkey]

Rubber fuel hoses dried out and leaking
a small amount of air in the vacuum side or packing on fuel pickup valve leaking air when engine running?

[Jentine]

I would suspect that one of the injector nozzles is clogged or leaking causing the roughness at idle. It may provide sufficient fuel at higher rpms but not enough at idle.
While the engine is idling roughly, loosen each of the injector nozzle lines just enough to cause the engine to run rougher. When you come to the faulty injector, the idle roughness will not increase. At that point, I would have the injectors serviced.
There are other reasons for the rough idle but this simple check will rule out the nozzles.

[Arthur Garfield]

Op said rough running started with one engine now rough in other.Bad fuel,H2O in fuel,air into fuel lines.that's about all that could be wrong.Injecter tips could
have gunked-doubt it.My $ on bad fuel.Did you fuel up-top off recently?

Oh,one more thing,my cumins's act up if I use unfamiliar oil!
Have you changed oil using different brand?

[whatever]

Thanks for all the suggestions! Will look into those tomorrow and follow up with what we find. What I can answer now is 3813hrs on motors, Starboard injectors rebuilt or replaced at a little over 3300 hrs. Port not touched. No smoke before rough idling, no smoke now. No water in filters. Only smooths out when rpms advanced to 900. No change in type oil used, port had a slight rough idle, fueled up and sat for a long while, then moved the boat from So Fl to NE Fl and had to get over 300 gallons while underway, holds 600. So it may be the injectors. If we don't move the rpms up, the motors will cut off. Question we have is how can we crack the injectors while running rough, if the motor will stop?

[motion30]

My bet on the iinjectors. I bought mine.from a place in miami. New for $55 each. Found them on ebsy

[whatever]

Changing them ourselves is beyond our scope

[Arthur Garfield]

If vessel sat for long time diesel may have gone bad.Injectors often are not culprit-injector TIPS(NOZZELS) go bad.As I said earlier-think fuel went south on you.I suppose entire understanding of reccent engine history needed
Perhaps place to begin is analysis of diesel fuel quality.Suspect fuel is culprit.

[whatever]

Where can I take a sample of the fuel to be tested? Are there places that do that?

[River Cruiser]

Originally Posted by whatever

Where can I take a sample of the fuel to be tested? Are there places that do that?

Cat dealer can most likely analyze a fuel sample. On cracking the injector line nuts while running the engine won't die but if there is no problems it'll run rougher miss on each good cylinder. If you crack a line and nothing changes you have a problem on that cylinder. If I was you with the hours on them I would adjust the valve lash and check the low and high idle RPMs to see if they are within specs. If the rough running is a noisy rattling at idle the problem may be worn drive plates and not the engines, the rattle goes away when the rpm gets around 800 to 900 rpm.


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[whatever]

The Captain drained some fuel out of the bottom from the Raycors and it appears ok, no water, correct color, correct smell and no particles seen by naked eye, of course that is not a scientific analysis by any means. The rough idle is not a rattling, it is a vroom, vroom, vroom, vacillating up and down (hard to describe in words). The problem I mentioned is if leaving the motor in the lower idle while trying to crack the nuts is that if it is left to the rough idle for very long at all, the motor will die. Captain is not all that mechanically inclined. Pretty much at this point, we have decided best to get a mechanic, being able to locate one that is good is now an issue. We are on the St Johns River in FL, in a less than adequate locale for qualified mechanics and more than likely will have to move the boat to get to someone. That in itself with the worry of motor dying on us when trying to get into a dock is a challenge. We shall see.

[whatever]

Also, Captain has adjusted low idle to 900 rpms(that seems to be the magic mark, as low as it will go without the fluctuation) the book suggests 1000 rpms as maximum at idle to avoid transmission damage upon shifting. Wondering if that is ok for trying to move the boat?