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Old 02-17-2019, 12:25 PM   #1
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Turbo lag

First off conditions to answer questions before they're asked:

Clean bottom(bottom job done 5 days ago...couldn't be any cleaner)
Prop pitch(perfectly...reaches 2900rpm WOT on a 2800 engine as measured by Aetna digital tachs)
Engines: Cummins 330B with 1500 hours
Load: less than half load
Air cleaner: clean
I have pyro and boost gauges
No black smoke at all even when right throttle is advanced to max while turbo is lagging.
I have not yet checked for blowby at oil cap. Not as easy as it seems on my boat...haha
Oil pressure: right engine is about 15psi lower than left....but it has always been this way in the 1200 hours I have owned the boat and well within spec.

Problem:
Right engine is slow to come up to boost. It lags way behind the left one and boost seems to come up as boat is getting up on plane. Obviously, RPMs lag as well. EGTs on both engines come up equally on both sides until turbo lag(about 700 degrees) then EGT on right engine lags. Once up on plane both engines stabilize normally and both engines give instant and predictable response to throttle inputs with normal engine indications.

Questions:

Is this a slam dunk turbo issue(I hope...turbo rebuils/replace is quite easy and not terriby expensive)
or:
Could it be a bigger issue with the engine just not producing enough heat(energy) to spin the turbo up....IOW a dying engine.

Thanks in advance!
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Old 02-17-2019, 12:50 PM   #2
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Try to spin the turbo with a finger. It should spin freely.
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Old 02-17-2019, 01:52 PM   #3
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Check for leaking connections between turbo and intake manifold.
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Old 02-17-2019, 02:14 PM   #4
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Just to confirm, the right engine's actual performance lags the left as well as the boost pressure? So it's definitely under-performing, and not just a different boost pressure reading?
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Old 02-17-2019, 02:57 PM   #5
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Generally if you're not getting enough boost (combustion air), I would expect to see black smoke out the back. When was the last time the secondary fuel filters were changed?

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Old 02-17-2019, 03:11 PM   #6
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Quote:
Originally Posted by twistedtree View Post
Just to confirm, the right engine's actual performance lags the left as well as the boost pressure? So it's definitely under-performing, and not just a different boost pressure reading?
I'm not really sure what you are getting at. Both engines did in fact perform similarly in the past. And they are not performing similarly now. The "boost pressure reading" does definitely lag the other engine. If you are wondering if it is an indication issue, it is not. Performance definitely confirms that it is real and not an indication issue.
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Old 02-17-2019, 03:13 PM   #7
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Quote:
Originally Posted by O C Diver View Post
Generally if you're not getting enough boost (combustion air), I would expect to see black smoke out the back. When was the last time the secondary fuel filters were changed?

Ted
Ted...that is a very good point and I was baffled by that fact/observation as well. It suggests that it is not getting enough fuel....and I had not thought of that. I was looking mostly at the "air side" of things. And you are suggesting it might be a fuel issue. Interesting!!!!
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Old 02-17-2019, 03:17 PM   #8
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Have you checked charge air pressure on both (boost)? If both are the same at full power and rpm close to the same, turbo is not suspect. There is a device on the injection pump that limits fuel until boost comes up, the setting could be different p/s
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Old 02-17-2019, 03:24 PM   #9
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Originally Posted by Ski in NC View Post
Have you checked charge air pressure on both (boost)? If both are the same at full power and rpm close to the same, turbo is not suspect. There is a device on the injection pump that limits fuel until boost comes up, the setting could be different p/s
Not sure I am understanding you. I do have a boost pressure gauges. And they are NOT the same on initial power up. The right engine is "flat lined" until the boat starts to clear "the hump". They are the same when the boat gets up on plane and everything is "stabilized". Once on plane both engines perform normally and as expected. But the left(good?) engine does most of the work getting the boat up on plane. Like Ted said, I was a little baffled/concerned there was no black smoke on the engine with the lagging turbo. I was thinking if it was strictly a turbo issue, there would be black smoke???
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Old 02-17-2019, 04:11 PM   #10
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With no smoke it is likely to be a fuel issue. You are not getting enough fuel to the lagging engine, at least on acceleration. That latter issue points to what Ski is saying above. The engine's fuel injector has a fuel limiter that pinches down fuel while accelerating to keep from dumping in too much fuel. It may be out of adjustment- Ski would know how to check it, or worn and bad.


The fact that both engines finally run at expected power at wot indicates that there probably isn't a general fuel restriction like a plugged filter.


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Old 02-17-2019, 04:14 PM   #11
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The lower oil pressure may be an indicator of the turbo lag.
Oil pressure entering a ball-bearing turbocharger needs to be between 40 psi and 45 psi at the maximum engine operating speed.
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Old 02-17-2019, 05:03 PM   #12
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does the engine have a air/fuel ratio control on the injection pump?
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Old 02-17-2019, 11:17 PM   #13
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does the engine have a air/fuel ratio control on the injection pump?
No clue....definitely beyond my pay grade.
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Old 02-18-2019, 06:55 AM   #14
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https://www.sbmar.com/articles/anero...njection-pump/

Here you go.
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Old 02-18-2019, 07:12 AM   #15
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Before you go down a rabbit hole with this look at the basics. Did this just start suddenly? If so check for something that may be hung up or corroded. Do these turbos have waste gates? One may not be closing completely. Salt water / salt air intrusion could be causing corrosion and thus causing one of the turbines / exhaust side to spool up slowly. ( see post 2). Look for split rubber hoses coming off or leading to the turbo and or waste gate. Messing around with the injection pump is above my pay grade. Maybe yours also? FWIW adjustments on injection pumps don’t change suddenly unless something is broken...... probably inside
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Old 02-18-2019, 07:13 AM   #16
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Quote:
Originally Posted by Baker View Post
I'm not really sure what you are getting at. Both engines did in fact perform similarly in the past. And they are not performing similarly now. The "boost pressure reading" does definitely lag the other engine. If you are wondering if it is an indication issue, it is not. Performance definitely confirms that it is real and not an indication issue.



Yes, that's what I was asking. Thanks.
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Old 02-18-2019, 08:22 AM   #17
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What happens if you push up the stbd engine alone with the good engine throttled back say 1000 rpm behind? Does the stbd engine eventually build up power or just stay flat? What Im saying is can the stbd engine build power without the "help" of the port? Ultimately, the source of engine power comes from the fuel system. Without smoke, lack of sufficient fuel makes sense. Make sure the filters are clean.
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Old 02-18-2019, 11:31 AM   #18
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Originally Posted by Cigatoo View Post
Before you go down a rabbit hole with this look at the basics. Did this just start suddenly? If so check for something that may be hung up or corroded. Do these turbos have waste gates? One may not be closing completely. Salt water / salt air intrusion could be causing corrosion and thus causing one of the turbines / exhaust side to spool up slowly. ( see post 2). Look for split rubber hoses coming off or leading to the turbo and or waste gate. Messing around with the injection pump is above my pay grade. Maybe yours also? FWIW adjustments on injection pumps donít change suddenly unless something is broken...... probably inside
Actually it did not start suddenly. It was intermittent in the fall. But we have had such a crappy winter that I have not used the boat as much as I normally do. No waste gates on these engines. Aftercooler was serviced about 6 months ago and reported to be "in better condition than I have ever seen" as reported by the tech....I do not defer mtx on those things. Adjusting injection pump is certainly above my pay grade...
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Old 02-18-2019, 11:34 AM   #19
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What happens if you push up the stbd engine alone with the good engine throttled back say 1000 rpm behind? Does the stbd engine eventually build up power or just stay flat? What Im saying is can the stbd engine build power without the "help" of the port? Ultimately, the source of engine power comes from the fuel system. Without smoke, lack of sufficient fuel makes sense. Make sure the filters are clean.
Nope...I haven't tried that....not sure the "good engine" could get the boat up by itself though.
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Old 02-18-2019, 11:45 AM   #20
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If the turbo and or the waste gate where bad you would not achieve full boost. Also you would have black smoke due to poor a/f ratio.



The fact that you make full boost at rated rpm tells me that the turbo is performing but the fuel is not being delivered when it's building boost. More often than not the diaphragm in the a/f ratio control will have a tear or crack. The a/f ratio control is designed to hold the fuel rack back till it has enough boost to overcome the spring. Then it allows the injection pump to achieve full fuel.



Beings your not familiar with the engine side. I would strongly recommend getting someone qualified to come look at it. I'm not super familiar with the Cummins pump's. Cat's are pretty easy to swap the a/f ratio control from one engine to the other and see if the problem fallows.
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