3126 Cat (350 HP) stalls above idle

[Stromeister]

Today we took our 2003 410 Sundancer out for a small trip and when we put her up on plane she ran fine for 5-6 minutes and then started to loose RPMs quickly. Brough boat down off of plane and the port engine barely idles and when you apply throttle on Port engine she boogs done and has load knocking noise. Brough boat back to her slip and replaced all Racors and fuel filters for both engines with no change. Water is pumping out side discharge and oil level is fine. Turned switches for tank selector to feed off the starboard tank and still no change. Just fueled up boat with fresh fuel 2 weeks ago and had her out and running fine since refuel. Suggestions on things I should look for before I call in a diesel technician next week?

 

[k9medic]

I had a similar problem. Turns out I had turned the selector switch the wrong way. Frank will chime-in in a bit I'm sure, but you may want to check that the vent lines are not clogged.

 

[HUMPH]

That sucks but probably an easy diagnosis. It has to be a fuel issue I imagine. Make sure your fuel valves are pointed at the tank and not to the off position. I have heard of fuel lines losing their rigidity and collapsing on themselves under load too. Check all of your fuel hoses.

 

[fwebster]

I'm in AC doing this on a phone so it is quick.

If you are sure both the Racors and Caterpillar engine mounted filters are clean the your problem is most likely a leaking injector seat. This is not an owner serviceable issue since the seat must be reamed with a special tool the. The injector reseated.

Hope that helps.

 

[Stromeister]

Thanks Frank and others. Trying to get the local Cat dealer technician here early this week. Appreciate the suggestions and is does sound like a fuel issue with either the injectors and/or seats. Will keep posted.

 

[Stromeister]

Had the local CAT Service Technician come and troubleshoot the issue and he indicated that several (4) of the injectors were not firing properly. Upon removal for inspection of the injector seats, he did not see any signs of "leakage" past the injector seats and was leaning towards faulty injectors. He replaced all 6 with remanufactured injectors and reamed the seats and adjusted the valve timing and such. Engine is running as good as new but I question whether the engine ran bad long enough for there to be signs of "leakage" and maybe just reaming the seats would have taken care of the issue?? Thoughts??


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[fwebster]

A diesel injector has to atomize, not spray fuel. Nearly anything on or around the injector tip and any trash inside the injector can affect the amount of fuel injected as well as the spray pattern. Since you didn't run the boat very long this way and since it occurred all at one time, there probably isn't enough history to cause a clear indication of the problem on a visible part of the engine.

On a Cat engine, replacing an injector requires reaming the seat, so if that was the problem, then it is fixed because you have new surfaces now. Removing an injector also requires re-setting the overheads, so there isn't much more that could be done here.

 

[Stromeister]

Thanks for the feedback, Frank.


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[markrinker]

Interesting scenario. How many hours on the CATs? Any sign of water or contamination on RACORs? How long since last fuel filter service?

 

[Stromeister]

Engine only has 200 hours on it. Previous owner did not run the boat very much at all (boat had 130 hours when we purchased). Serviced the racors as well as the fuel filters when we purchased June of last year as well as when we put her away for the winter last November. When the symptoms appeared, we changed the racors and filters again with no change.. Will be monitoring the the racors and treating the fuel for the next few months/tanks of fuel.


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[markrinker]

Engine only has 200 hours on it. Previous owner did not run the boat very much at all (boat had 130 hours when we purchased). Serviced the racors as well as the fuel filters when we purchased June of last year as well as when we put her away for the winter last November. When the symptoms appeared, we changed the racors and filters again with no change.. Will be monitoring the the racors and treating the fuel for the next few months/tanks of fuel.


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Food for thought...out here in Seattle we get lots of rain and (usually older) boats that don't get used much develop water (leakage from deck fills, condensation) in fuel tank problems. Injectors suffer immediately and are often damaged when water makes its way past the Racors and into the injector pump.

With the crazy low hours on this boat, the mystery to me is why all of a sudden you'd develop a couple bad injectors? Any signs of water in your Racors?

 

[ttmott]

As it ends up I just went through a similar situation and am now finally getting through the issues. After fueling up in the Bahamas last September and having run out of fuel treatment (Bio-Bor) the tanks developed a significant algae situation. Actually, in looking back there has been a problem since I purchased the boat but it was manageable by routinely changing filters. Regardless, the starboard engine would loose RPM and eventually stall. As it ends up after months of chasing the issue three things contributed.
One, the Racors that were originally (500MA) are grossly undersized for the engines; my mechanic told me from the beginning to install the bigger 900's so I finally did that.
Two, the fuel hoses were not configured correctly and the port tank hoses were swapped on the selector valve and the starboard engine feed and return hoses were also swapped on the selector valve which mucked up the entire selection process for both engines. We found out that as fuel coolers were installed on some engines and not on others the return bung on the fuel tanks has a dip tube so who would have known? Regardless the selector valving has smaller ports on the return side restricting supply and any switching would take return fuel from the one engine to feed the other. From what I can tell it was routed this way from the beginning.
And three, the algae was plugging up the pickup tube in the fuel tanks. After a stalling event noticed bubbles in the racor filter which indicated either an air leak or very high vacuum which vaporizes the fuel. First I put a vacuum tester on the fuel system supply hose at the engine and pulled down to 30 inches of water with the fuel tank valve closed and it held for 30 minutes which indicated no air leaks in the hoses or valving; Then I opened up the fuel tank valve still with a vacuum on the system and it still held the vacuum; Well there you go there is something plugging the line in the tank. I disconnected the hose from the racor inlet and blew compressed air back through the entire fuel feed system to the tank; pressure built up then "kaboosh" it blew whatever was plugging up the feed back into the tank. As a note you cannot blow back to the tank through the Racor filter assembly as there is a check valve in it. A secondary problem then revealed it's self where the starboard racor filter had a small air leak on the bowl gasket.
So, where are we at today - I built a polishing system using the old 500 Racors and a high flow fuel transfer pump and circulated fuel for about 5 hours for each tank while adding a shock level of fuel algae treatment. Also transferred fuel back and forth to the two fuel tanks. Fixed the fuel hose configuration. Replaced the Racor 500's with 900's. And I keep close tabs for any air bubbles and algae in the fuel filters. The contamination in the Racor elements has gone down to where I think we are back to a normal condition.
Hope this helps.....