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Cummins 370 power loss.

DIESEL engine, transmission and generator repair and maintenance discussion forum.
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Tomion
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Cummins 370 power loss.

Postby Tomion » February 10th, 2018, 11:56 pm

Hello, My port engine has been losing power a little bit at time over the last year since I had my prop shafts and bearings replaced. It started with just a slight lag to the starboard engine and has progressively gotten worse over the past year. Now it maxs out at 1800 RPMs and boat cant get up on plane.

Runs very smooth, no smoke even under load at 1800 RPMs Motor will spool all the way up to 3000 RPMs in nuetral.

I have confirmed fuel tank is venting properly
I checked throttle cable travel and it matched the staboard engines
I replaced the engine fuel filter
The engine runs very smooth at all RPM ranges and does not smoke.

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Re: Cummins 370 power loss.

Postby mjk1040 » February 11th, 2018, 6:49 am

If both engine act the same in neutral, then I would be leaning toward the shaft & bearing replacement issue. Something reinstalled wrong or out of alignment. Do both shafts turn by hand the same? Reason for shaft and bearing replacement? Did this reason maybe effect the transmission? Keep us posted. Sorry I don't know of a specific fix for you.
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Re: Cummins 370 power loss.

Postby bud37 » February 11th, 2018, 1:00 pm

If you want to cross of the shaft issue, just crawl down there and turn them by hand and compare sides as has been mentioned.....the only other thing that comes to mind would be the air intake system for that engine has maybe become restricted,possibly get smoke from that though...hows the trans fluid look??....just a shot in the dark for ya.

Post the year of your engines, may be a help for someone to diagnose for you.

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Re: Cummins 370 power loss.

Postby Viper » February 11th, 2018, 5:36 pm

Tomion wrote:Source of the post......I replaced the engine fuel filter......

I trust you mean the filter on the engine itself. Do you have primary fuel filters such as Racors before the engine? If so, have they been replaced and the assemblies cleaned?
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Re: Cummins 370 power loss.

Postby Tomion » February 12th, 2018, 11:10 am

The engines are 2001 mechanical fuel injection. The bottom was painted a year ago when they found the castle bearings were shot and they had worn groves in the shafts and they had to be replaced. I find it odd that it has gotten progressivley worse over the last year. There is no vibration, will check to see if I can turn shafts by hand. The Racor filters look clean thru glass bowl so I dont think it is dirty fuel issue. I beleive the only explanation beyond a shaft issue is a turbo but have been told engine would smoke a lot if this was the priblem.

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Re: Cummins 370 power loss.

Postby Viper » February 13th, 2018, 6:48 am

Tomion wrote:Source of the post........The Racor filters look clean thru glass bowl so I dont think it is dirty fuel issue.....

Sounds like a fuel delivery issue. The bowl might look clean but you may have a restricted filter if it hasn't been changed in a while.

Tomion wrote:Source of the post....... I beleive the only explanation beyond a shaft issue is a turbo but have been told engine would smoke a lot if this was the priblem.

Correct, not enough air for complete combustion to burn all the fuel.

Tomion wrote:Source of the post...... Now it maxs out at 1800 RPMs and boat cant get up on plane......Runs very smooth, no smoke even under load at 1800 RPMs Motor will spool all the way up to 3000 RPMs in nuetral......

Running it in neutral at 3000 rpm is not the same as running it in gear under load. BTW, it not a good idea to run an engine at that rpm in neutral.

Short of a fuel delivery problem, there aren't many other suspects except internal issues like poor compression.
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Re: Cummins 370 power loss.

Postby bud37 » February 13th, 2018, 12:33 pm

Tomion wrote:Source of the post The engines are 2001 mechanical fuel injection. The bottom was painted a year ago when they found the castle bearings were shot and they had worn groves in the shafts and they had to be replaced. I find it odd that it has gotten progressivley worse over the last year. There is no vibration, will check to see if I can turn shafts by hand. The Racor filters look clean thru glass bowl so I dont think it is dirty fuel issue. I beleive the only explanation beyond a shaft issue is a turbo but have been told engine would smoke a lot if this was the priblem.

I agree with Viper above there.....here is some additional info and a good read for you,I know it was for me; You may have come across this but nevertheless......

https://www.sbmar.com/articles/understa ... eshooting/
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Re: Cummins 370 power loss.

Postby Tomion » February 24th, 2018, 7:40 pm

Thanks for all your input, got back in town this week and had mechanic check out engine.

1- Shafts turn easily on both engines.
2- Transmission fluid levels good.
3- Mechanic pulled intake and exhaust sides of Turbo and found it to be free and in good condition.
4- Checked Racor filter, found to be clean.
5- returning next week to check fuel pressure

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Re: Cummins 370 power loss.

Postby Viper » February 24th, 2018, 7:52 pm

Thanks for the update. What year is the boat and how many hours on your engines? How long have you owned the vessel, and about how many hours on average would you say you put on her in a season/year?
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Re: Cummins 370 power loss.

Postby PJHoffnet » February 25th, 2018, 10:00 am

Please forgive my ignorance, I don't know the specifics, but I'll try to recall what my mechanic he said he found/replaced. Someone with more diesel knowledge will be able to fill in the blanks hopefully.

Had an underpower issue with my starboard Cummins' 330. Like you, port ran fine, had clean running gear after a scrape, and engine ran fine in neutral. Under load, wouldn't go over 2K RPM (recommended max is 2.8K). Mechanic believed turbo was at fault - not kicking in properly.

Here's where I hope some gear heads will jump in. At lower RPMs, turbo acts fine ... at higher RPM (a 'second' boost phase from the turbo?) he spotted a leak in a hose (and here's where I lost him) ... used the words turbo and aftercooler. I have a operations manual, but I can't really tell what hose he might have been talking about - replaced. BUT - replace it he did and now things are rockin' and rollin' like they're supposed to - 21knts up on plane in a heart beat, both engines purring at 2.8K RPM.
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