Loss of Power

[Jeffrey Cohen]

I have 2008 5.9 QSBs (425hp) with approx 650 hrs and the port engine just developed an issue.

So here’s the situation:

Day -7: Rough trip back to the dock in rough/choppy bay but everything seems ok (seat of the pants assessment but I wasn’t looking for an issue).

Day -1: 1 hr run to marina and noticed that both engines seemed to be ‘off’ (boat not traveling at usual speed at usual RPMs and GPH slightly elevated) but can make full RPMs (3030) so I shrug it off and assume there is a current working against me.

Today: On the run back to home port I run the engines at WOT for 1-2 minutes as I always do to make sure all is OK and after about 30 seconds the port engine drops to 1500 RPM. I drop anchor and discover that a hose clamp failed so the exhaust feed to the turbo is no longer attached. After replacing the hose clamp I notice that the port engine is now struggling versus the starboard engine because it is burning more fuel to make the same/sync’ed RPMs by about 1.5 GPH. So I tried to bring both engines up to WOT and the port engine can only make 2950 while the starboard engine makes the full 3030. Back at the dock I try to bring both engines to WOT with no load and both spool up to 3060.

I have no idea what to look for so my plan is to replace all the fuel filters tomorrow and take it out for a test run.

Does anyone have any other ideas of what I should be checking so that I don’t lose time on the water?

TIA

Jeff

Topic

[Tony Athens]

Loose Boost = ECM limits fuel = limits HP = LIMITS RPM. Tony

[Jeffrey Cohen]

Rob Schepis wrote:

Jeffrey Cohen wrote:
I mean the hose that comes off the bottom of the intercooler that powers the turbo.

Sounds like you mean hose #2. That is compressed air LEAVING the turbo compressor going thru the aftercooler and into the intake manifold. The only thing that “powers the turbo” is the stream of exhaust out of the exhaust manifold and into the turbo turbine.

Yes…I goofed that up.

Anyway, I went to the boat today and replaced both fuel filters on that engine (10 micron Racor and the 2 micron last chance filter on the engine). This had no affect so I took a closer at the silicon hose that unions the stainless steel tube to the turbo (blue #2 on the attached image) and it had a tear in it (I presume this was from the original hose clamp failure) which was the cause of secondary loss of power. I have since replaced it and all the clamps and now all is good.

Thank you all for your input and help.

Jeff

[Philip]

Something like this makes filter inspection really easy….

https://www.speedwaymotors.com/Speedway-Engine-Motor-Oil-Filter-Cutter-Tool,2618.html?sku=91081031&utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gclid=EAIaIQobChMInLu5vorH3AIV6xXTCh3n8QMVEAkYBiABEgKEn_D_BwE

[Rob Schepis]

Jeffrey Cohen wrote:

I mean the hose that comes off the bottom of the intercooler that powers the turbo.

Sounds like you mean hose #2. That is compressed air LEAVING the turbo compressor going thru the aftercooler and into the intake manifold. The only thing that “powers the turbo” is the stream of exhaust out of the exhaust manifold and into the turbo turbine. We are all here to help but you should really use all of the info on this website, and Google and/or buy a book and get a 100% understanding of all the workings of the engine as to what is what and what does what. it will pay dividends to your troubleshooting and understanding on where to look when things are not quite right and will help you digest what you read here and put it to practical use.

Based on your performance specs seems propping is good. Yes a filter change is in order because the fouled filters do effect the math that puts the numbers on the screen. Easy to cut the filter open – go around the perimeter with a hacksaw like this.

[Jeffrey Cohen]

Philip wrote:

And what’s the service history of the engines. Often times a hose that comes off the turbo to aftercooler connection is indicative of a clogging aftercooler. When was the last time the aftercooler was serviced and exactly how was it serviced? Also what are the condition of the connection hoses and clamps? At a minimum get a screwdriver on all the clamps and ensure all are tight. Consider new hoses and clamps if they are older.

Phil

I serviced them myself at the end of the season before last (1.5 seasons ~150 hours ago) as per Tony’s guidelines. This was my second time performing this work on the aftercoolers.

The hose clamp that came off just snapped in the middle…I probably tightened it too much as there was no corrosion whatsoever. I think it’s a good suggestion to start replacing the rest of the hose clamps.

Something similar happened at the beginning of last season right after i served the aftercoolers…except in that case I totally forgot to put back the hose clamp on the turbo feed side of the aftercooler on the starboard side. But in that case the engine operated perfectly after I reattached the hose. That is how I knew exactly what had happened.

Now I am trying to diagnose the elevated fuel burn on that engine. I have no idea if it is related or it’s just a coincidence.

Thanks for the input and suggestions.

Jeff

[Jeffrey Cohen]

As to the the one on the engine–if it was me , I’d dump it into a clean bowl and “look & see”.. Then, I’d cut it open and “look & see”..

Will do

[Philip]

And what’s the service history of the engines. Often times a hose that comes off the turbo to aftercooler connection is indicative of a clogging aftercooler. When was the last time the aftercooler was serviced and exactly how was it serviced? Also what are the condition of the connection hoses and clamps? At a minimum get a screwdriver on all the clamps and ensure all are tight. Consider new hoses and clamps if they are older.

Phil

[Tony Athens]

Replace all fuel filters as you said–

As to the the one on the engine–if it was me , I’d dump it into a clean bowl and “look & see”.. Then, I’d cut it open and “look & see”..

But that’s just me..

Tony

[Jeffrey Cohen]

Rob Schepis wrote:

Did you mean a boost hose? Air intake coming off the turbo?

Post your fuel burn numbers at cruise range rpm’s and WOT rpm.

Do you have data of “X speed at X rpm” ? – both historic and now?

Post some good pictures of your engines, the installation and the exhaust.

BTW, not following your format of Day 7, Day 1, today ..

I mean the hose that comes off the bottom of the intercooler that powers the turbo.

My boat has been very consistent since the day I launched it….
2500 RPM
25 GPH (12.5 GPH each engine)
25 Knots (SOG)

Right now, at 2500 for each engine, I am seeing 14.5 GPH for the port engine and 12.8 for the starboard engine but the port engine is not settling in (keeps hunting around 2500 +/- 30 RPM) so the starboard numbers are suspect.

As for the format…. Day -7 was last weekend return to home port Day -1 was yesterday and today was today.

I’ll report back on once I replace the fuel filters on the port engine and check all the hose clamps and clean the airsep. I will grab some pics too.

Thx
Jeff

[Rob Schepis]

Jeffrey Cohen wrote:

I drop anchor and discover that a hose clamp failed so the exhaust feed to the turbo is no longer attached.

Did you mean a boost hose? Air intake coming off the turbo?

Post your fuel burn numbers at cruise range rpm’s and WOT rpm.

Do you have data of “X speed at X rpm” ? – both historic and now?

Post some good pictures of your engines, the installation and the exhaust.

BTW, not following your format of Day 7, Day 1, today ..

[Author]

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