Author Topic: C9 runs great for 45 minutes  (Read 543 times)

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Offline BobzCat

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C9 runs great for 45 minutes
« on: August 07, 2019, 07:02:40 PM »
I've got a C9 serial range 9DG in my 2005 American Tradition.  No emissions controls of which I am aware.  Scangauge D showing HP, boost, oil pressure and average MPG.  Just over 102k miles.

From a cold start, it runs like a dream.  Boost and HP fluctuate with throttle, plenty of power,  Allison shifts as needed.  No problem with hills.

After ~45 minutes,  it goes into "normal" mode.  HP will vary, but boost is constant in the 11-13 lb range.  11.4, 11.7, 12.4, 12.6 have been noted, even at idle/stopped.  Throttle gives very little power increase, although. HP will vary.  Climbing hills, I manually downshift to keep momentum.  When I shut down for fuel or rest, it may start in "good" mode but within about 5 miles goes back to "normal " mode.

Average MPG gets up to about 6.6 on a good day, otherwise 6.2 range.  I use Biobor and XPD Summer as additives.  Engine temp reads 201 normal.

Suggestions on things to look for/at?

Thanks,  Bob

Offline David.e.atherton

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Re: C9 runs great for 45 minutes
« Reply #1 on: August 08, 2019, 12:49:58 AM »
Bob, good job making note of boost pressures . Let’s start engine running at idle, and
there is a reading on gauge where at idle there is not to be any reading. When numbers
at idle need to be reading zero and low power. ( boost pressure sensor ) first,  second,
Boost pressure regulator. Third wastegate sticking and will not open to max 32 psi
Ask Dave, Dave Atherton Retired Cat Mechanic

Offline BobzCat

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Re: C9 runs great for 45 minutes
« Reply #2 on: August 08, 2019, 05:09:22 PM »

Thanks for the reply. Well, today it started in normal mode.  Sigh.

On a good day...
Startup boost is 0.1 HP is 0.0 at idle.
Driving, max boost seen is about 29  max HP remembered is 330+

On a bad day...
Startup/idle boost is 11-13 HP is 0.0 at idle.
Driving, boost stays at one value in the 11-13 range, today HP 230+
Today, downhill,  HP 0.0  boost 12.0  MPG 9999

On a good day, the wastegate seems to work fine.  Why would it intermittently stick?  Is it something I can hit with lube?

What would make any of the three suspects fail after (generally) 45 minutes of working properly?

I've got a 600mb video of my scangauge on a bad day, but I don't think I should post it.