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Old 01-21-2021, 06:53 PM   #1
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400hp ISL turbo boost questions

How much boost is your 400hp ISL making?
Mine doesn't seem to run as well as I think it should, in fact my previous 325hp larger slightly lighter coach ran much better.

I have done all normal maintenance and power has not improved. The things I have noticed is my boost guage seems higher than I would have expected. At idle I see close to 5psi, reving motor in neutral will rise near 22psi, driving it often goes well over the 30psi max on the guage. This is a mid year 2004 non emissions Monaco so I doubt its an exhaust restriction like you'd expect from a plugged cat? You can also hear the turbo whistle at idle from the exhaust which seems unusual?
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Old 01-21-2021, 07:15 PM   #2
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My 2008 which is a 425 hp produces max about 32 to 33 pounds.
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Old 01-21-2021, 07:45 PM   #3
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Sounds like your boost is pretty normal. How heavy is the coach?
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Old 01-21-2021, 09:38 PM   #4
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I never see more than 23 on a non emissions 2004 isl. Been the same for 3 years, checks out with the manual iirc.
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Old 01-21-2021, 09:42 PM   #5
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It's been a long time since I had the 400 ISL, but if I recall, it was right around 30 psi. My 450 ISL (L9) will max at 34 psi.

"shootist".....you either have a bad gauge or turbo issues!
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Old 01-21-2021, 09:47 PM   #6
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If I remember right my 500 ISM is about 25 psi
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Old 01-22-2021, 12:40 AM   #7
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CAPS, with non vt turbo should be 23.8 ideally. I believe a waste gate adjustment sets it. I could be wrong on the wastegate as I've never actually worked on one. The variable turbos have increased boost pressures from what I've read. Non egr, non vt, caps you would be high. Either common rail or vt has higher boost.
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Old 01-22-2021, 10:47 AM   #8
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Quote:
Originally Posted by shootist View Post
CAPS, with non vt turbo should be 23.8 ideally. I believe a waste gate adjustment sets it. I could be wrong on the wastegate as I've never actually worked on one. The variable turbos have increased boost pressures from what I've read. Non egr, non vt, caps you would be high. Either common rail or vt has higher boost.
This is important^^.

The OP has a "mid year 2004". That means he could have the CAPS or the Common Rail, depending on year of the engine itself. We need to know the year of the engine to assess whether or not his boost is correct.
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Old 01-22-2021, 11:31 AM   #9
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I called Cummins and asked what they show for the max boost for my ISL400.

They said that it should be 26#. That is what I get for a reading on a ScanGuage D. The throttle position indicator is close to 100% at the 26# reading.
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Old 01-22-2021, 12:05 PM   #10
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My engine was manufactured in March of 2004, hope that helps
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Old 01-22-2021, 12:54 PM   #11
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Quote:
Originally Posted by bearscat View Post
My engine was manufactured in March of 2004, hope that helps
I believe that makes it a Common Rail engine (others can verify), and so would have the higher boost rating. Your engine serial number will confirm, or a picture of your fuel pump.
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Old 01-22-2021, 01:12 PM   #12
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24 for a 03 CAPS ISL 400 and 32-34 for 04 common rail.
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