Need help to diagnose CAT problem

[Michael Volle]

I have Tiara with 3208 TA 375HP cats I have one engine with a power issue that we can not diagnose. At about 1900- 2000 RPM boat planes and both motors do OK… But as throttle is increased , say around 2200, the port engine rpm does not equal the STB at the same throttle position. The more throttle the worse this becomes until you hit WOT. should be 2800 however STB reaches 2750 but port will only reach 2450-2500. you can feel the stb motor increasing the speed but if you move the port motor it seems not power over that 2200 or so rpm. no smoke is apparent at any rpm or if there is its very very minor. The low RPM motor (port) is burning more fuel than the starboard. this condition is NOT from wrong props or anything like that as these motor ran great together at one time and no modifications have been made. One other little caveat . The port motor seams to be running slightly hotter than previously. maybe 5-10 degrees. Any ideas from anyone??

Topic

[Philip]

Again, working on pure diesel theory as I know next to nothing specifically about CAT….

My first thought is it’s a fuel delivery issue. Thus why I was suggesting you spend some time with vacuum and or pressure gauges to diagnose the health of the fuel system. Often times a restriction or a failing pump will not support engine rpm above XXX rpm but run just fine below whatever number XXX is….so you could be looking to rule out a weak lift pump, a clogging fuel line, etc with the vacuum and pressure readings. Those vacuum/pressure reading will have to be under load to get good info. You will have to do some learning of your fuel system to figure out if vacuum or pressure is to be measured and where as I just don’t know the specifics on your engine.

Of course I am assuming things like throttle cable adjustment are up to snuff.

It’s probably not air related else you would have lots of black smoke. So you can rule out aftercooler health and turbo condition. Both of those would show black smoke which your not getting.

What’s the service history of your fuel system? Type of filtration? Micron ratings of filters? Etc…

As Tony mentioned, pictures are always helpful…

Phil

[Michael Volle]

I’m measuring fuel usage using flowscans…

speed at 2100. is about 16 or 17 k….. that hasn’t really changed……its above that… at 2300…. port throttle is maybe 1 inch more then stb…..at 2500…port throttle can go to wot….and can’t make it there

[Tony Athens]

Quickie–Exactly HOW are you measuring GPH on the engines?

1) With only 100 hours over 3 years, I’m scratching my head as to how you could have established any time of base line.

2) Next–2100 RPM = what vessel speed last year? …………………………2100 RPM now = what vessel speed ???

Tony

[Michael Volle]

More info

Hey guys ill try to answer your questions. we have checked most of the obvious things.

shafts spinning easy, props just redone….again.

to answer tony

1. wot is 2800 at about 30 K as to past performance both engines worked as a pair and ran up evenly. 2400 would give about 24k…

2. I have owned the boat for a little over 3 years. they have about 1500 hours, but are 20 years old .. ive put maybe 100 hours on them in 3 years.. they start up every time

3. issues with the port motor started about a year ago.

4. as far as dark smoke it isn’t noticeable. you can look back when at cruise and see a lingering light smoke but cant noticeably see it coming from either engine … although it has to come from one or the other.

5. both engines come up to about 2100 ok….then you can see when you push the throttle on the stb motor… it come up to full power and speed increases proportionally when you do that to the port… you feel the motor is not increasing power. the thing that has been confusing is the increased fuel consumption, loss of power and slightly hotter temp , without black smoke … seem to contradict itself…. sigh

[Tony Athens]

Per Lukes and Phils post, you need supply a lot more before you are going to get help…

1) All the specs on the boat as speed and WOT RPM . Past vessel performance at 2200-2400 vs. now?

2) How about pics of the engines as installed in the boat–Let’s really see what you have and how the engines have been cared for over the last 20+ years..

3) How about past operational history a to speeds/RPM’s, etc–How abut when the issues started on the suspect engine?

4) How long have you owned the boat? Total hours now vs. total hours you have put on them??

5) Let’s talk about dark smoke for both engines………

Five questions–let’s have 5 good responses so Luke and Phil can help

Tony

[Luke Nelson]

Can you turn the prop shaft in the pen and is it as easy as the stb side?
I would check boost pressures as well. I could be a lot of things.

[Philip]

Disclaimer – I’m no CAT expert, really know very little…

I would start with some vacuum and pressure gauges on the fuel system comparing port and starboard readings under load. Vacuum at the primary boat filter and then again either pressure or vacuum at the last chance filter depending on fuel system design.

Phil

[Author]

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