Cat 3116 looses power - fuel leak?

[EKM]

So, after 1.5 hours of cruising, my port engine goes from 2300rpm to 1200+/- rpm. Bring the other engine down to idle and let it idle for a minute or so and put the boat on plane again...no problems on the rest of the trip (~1hour). My engine hours are 300 and had the valves adjusted at 250 hours. This is not the first time this has happened...last year, it happened 2x. I'm getting ready for a extended run, so I'd like to solve this. Racors changed and they were clean. I put vacuum gages on the racors and ran both engines, then turned the tank valves off until the gages had 8 " hg on them. The port engine leaked down from 8 to 2" hg within 10 minutes. The starboard leaked down from 8 to 5" over a hour + period. This of course can be the tank valve leaking slightly. I just replaced the primer pumps last weekend hoping this was the source of the leak.

On the primer, which position is off (should be like any other valve - 90 degrees is off)?

Am I looking for a leak in the fuel supply? There is the same boat and year at our marina and he had leaks with the fuel transfer manifold and ended up removing it. He had similar symptoms with intermittent lose of power until his port engine would not start up.

What is the best way to troubleshoot? I was thinking about disconnecting the fuel supply from the tank and pressurize it and soap each joint? what pressure is the fuel system hosing good for (50 psi)? any other suggestions? any chance that the gaskets in the Racors are leaking?

Thanks....

 

[Dancin Dave]

Have you removed the racor housing from the boat and disassembled it to clean? there is a ball and gasket kit that may need to be changed, you will be surprised how much crap can be in there even with the filters being clean, it can be deceptive. I dont think 50lbs is a good idea.

 

[EKM]

I had them all the way apart two years ago. I also have vacuum gages on the racors (just installed to help troubleshooting). This gages measure vacuum in the fuel system from the racor back to the tank.

I need to take the boat out again to see if the port pulls more vacuum.

so what exactly am I looking for? don't mind pulling them apart again?
Thanks....

 

[Dancin Dave]

do the gauges read the same after every run, Parker Racor told me 1 would always be higher than the other as they a plumbed differently and never remain on zero. What are yours doing?

 

[fwebster]

Ed,

You aren't going to like it, but.................

You most likely have an injector seat leaking on the #3 or #4 cylinder on the port engine. The seat leaks combustion gasses past the injector and into the fuel rail or cavity and, since air is compressible, that kills every cylinder after the one leaking.
It is just like having an air leak on 1/2 your engine.

I am sure enough that I'd suggest you stop fooling with the fuel system until you have Caterpillar come and check the engine. This isn't a repair you can make since the injector must be removed, its seat has to be reamed with a special tool, the injector reseated, then finally, the valves and injectors reset on that engine. Its is about a days job and the engine will be better than new when it is done.

Do not take the extended trip until you fix it because it can't heal itself and is only going to go from where it is now to the engine starting and running on 3 cylinders.

 

[EKM]

I just put them on...trying to troubleshoot this issue. So this weekend, I will do a sea trial. The boat going with me to BI had the gages...he has all the toys. When you rev the engines to 2000 (no load) the gage only reads about 3" hg which is in the good zone. But I should really sea trail to define reading at load. I was just wondering if anyone had experience with troubleshooting this type of failure.

I read one of the older posts in which FW pointed to injector malfunction in cylinder 5 or 6.

I really don't want to do the outside run without solving this problem but it also has been an intermittent issue.
Always something....

 

[EKM]

Ouch... your right...don't like it...hoping to troubleshoot everything else before calling in the high priced talent. Any way to define if the injector is the case? Sight glass in fuel system return? Pressure testing the fuel supply manifold should not take too much time.

Any guess at what pressure I can test the fuel supply system?
Thanks....

 

[EKM]

Dom....who do you use for your Cat repairs? I'm sure you mentioned your
CAT mechanics name but I wasn't paying attention....all that talk about bullet proof Cats. Maybe I need to buy a hat or Cat mat for it to run better??

Ed

 

[fwebster]

Your fuel system has proven to be ok since you ran the boat for a while at cruise speeds. Once you get air in the system, the Racor empties so if your Racor was full, that pretty much eliminates problems in that area. Continuing to do stuff to the fuel system is going to cause the Cat guy to have to go behind you and check everything your done.

Yes.......the return should have bubbles in it and it is a simple quick easy test for Cat to do.

 

[EKM]

Makes sense....in washing my boat this weekend, the port side seemed a little more dirty than the starboard side. Is this a tell tale?

Can I put in a sight glass (refrigeration type) in the return line to prove this out?

Should both engines be done or just one? Its been two years since the 250 hour service and now has 290 hours.
Thanks again for the guidance...

 

[osd9]

.......Its been two years since the 250 hour service and now has 290 hours....

There's your problem....20 hours a season!!!!!....you need to use the boat more....

Ed...I sent you a PM with regard to my CAT Mechanic....preface it with...."My first call is to Frank W"...you've already done that...

 

[EKM]

No kidding on the use. Fixing that this year....BI, MV and NPT cruise in a few weeks. Planning straight shot if weather permits (traveling w another boat).

 

[EKM]

Do they pull all the injectors and reseat them or do they find the one that is leaking? Looks like some expensive tools to pull this off....

 

[osd9]

Ed....I'm still waiting to hear back from the mechanic...

 

[fwebster]

It does take some specialized tools and a special reamer. It doesn't make sense to only do one on a head. The injector seats are done with a machine when the heads are built. Re-doing them by hand gives you a new, fresh seat for each injector plus it also allows you to have each injector checked since they are already out of the engine. It will take 6 hours to do one or 8 hours to do them all..........why not for an extra hundred $ or so.

 

[osd9]

Ed....I'm still waiting to hear back from the mechanic...

Calling your cell now.....

 

[EKM]

Tiny bubbles !!

Put a sight glass in the return line....bubbles. Moved it to the supply line....bubbles. Replaced the "O" ring in the tank valve transfer it was leaking...but still have bubbles. The hunt continues tomorrow am. Lots of fuel line to trace out...plan on putting a jumper in from the tank to the Racor and see its solved.

Also planning to check the good engine to see a baseline. I spoke to a CAT mechanic and he mentioned once he found a crack in the tank pick up tube (not on a SR product of course) but required engine removal.

 

[fwebster]

"plan on putting a jumper in from the tank to the Racor and see its solved. "

I don't follow this.........besides, it appears to be an unnecessary move since the Racor bowl is clear and you should be able to see bubbles in the canister if the line is leaking ahead of the Racor.


Bubbles in the supply line would cause the Racor to eventually run out of fuel and that will cut your rpms to zero since it would affect all 6 cylinders. You have an intermittant shut down of 1/2 your fuel supply............I'm still betting on a leaking injector seat.

 

[osd9]

Ed:

Checking the good side for a baseline is a good step. However, if it tests out clear, then that would suggest that you don't have an intermittent problem, you have a constant problem that 'sits' on the edge.

 

[Progress]

Leaking injector seats may also be indicated by a layer of deisel fuel floating on top of coolant in the coolant tank. If so you may want to flush the coolant to save your hoses.