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Old 07-15-2010, 09:17 PM   #1
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How Long do You Wait before Using Fast Idle

Following a cold start of my 400hp ISL, I usually wait a few seconds until I see the oil pressure come up before setting it on fast idle but I'm wondering if that might be too soon. Should I give the engine a full minute or so before kicking on fast idle?
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Old 07-16-2010, 01:44 AM   #2
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I kick up the idle as soon as the oil pressure comes up. If it didn't within a few seconds, I'd be shutting it down.

There's no real load on the engine at fast idle, so I don't think there's any reason to wait longer.

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Old 07-16-2010, 08:03 AM   #3
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As soon as there is oil pressure.
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Old 07-16-2010, 01:57 PM   #4
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As long as the oil pressure is not pegged high I put it right up.

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Old 07-16-2010, 02:56 PM   #5
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There is a known problem happening with that motor with cracked manifolds: Cummins 400hp ISL.

Cummins recommends waiting for a warm-up period before moving and the same before turning it off. If someone has additional details, please post.

Question: Why put the motor to a fast idle? and so quickly?
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Old 07-16-2010, 03:40 PM   #6
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I go to fast idle as soon as the oil pressure comes up. If it's cold, the ECM brings the fast idle up a little slower.

Fast idle=faster air pressure build up.
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Old 07-16-2010, 06:41 PM   #7
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3-4 Minutes at low idle.
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Old 07-16-2010, 06:54 PM   #8
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This is a question I ask at every major Cummins shop and it is about the only universally commonly answered question. I probably have a record of a couple dozen of all the same answer.

Every time the answer has been: yes DO use fast idle after a cold start AND it is best to go to fast idle AFTER the oil pressure comes up AND the pressure stabilizes.

So there is no exact time delay, just when the pressure needle settles in at the top of the scale. Then, mosey your fingers over to the fast idle button and kick it on. For me this is maybe 15-30 seconds or so, though I never timed it.
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Old 07-16-2010, 07:02 PM   #9
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the fast idle will help keep gunk from building up in your pipes
while your idling, I've always kicked on the fast idle soon
as I see all my gauges are reading correctly.
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Old 08-12-2010, 09:35 PM   #10
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This is great to know....amazing what I learn on this site!
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Old 08-13-2010, 03:41 PM   #11
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if its warm i kick it up after oil pressure stabilizes....if i need to recharge the air, if not i let it idle along for a few before departing

if its cold the ecm waits for a few things it does then it will ramp it up well over the high idle speed, in fact it sounds like a jet on takeoff full power
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Old 08-14-2010, 08:57 AM   #12
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Quote:
This is great to know....amazing what I learn on this site!
A word of caution: just because you see it here does not mean it is true. Many of us (myself included) have cherished opinions that we may not have any scientific or engineering evidence to back up, or that may have been true at some point in time but no longer apply to modern engines and systems.

The ECM (computer) in a modern diesel does a pretty good job of setting fuel mixtures and RPMs, including idle, without any assistance from the driver. I nearly always let mine handle the engine management chores.

This remark is not aimed at any particular message or advice - just a caution against embracing everything and anything you "learn" on an internet board.
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Old 08-14-2010, 09:30 AM   #13
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Originally Posted by RV Roamer [Gary] View Post
A word of caution: just because you see it here does not mean it is true............
............. just a caution against embracing everything and anything you "learn" on an internet board.
I know that I read somewhere, on the Internet, that everything posted there was "truth". I read it on the Internet, so it must be true!!! LOL!!!

Honestly, I have heard people say that--- and mean it! The first time I heard it, about 12 years ago, my mouth dropped open. Sadly, I still hear it- from time to time..........

These are the same people who answer those e-mail from x country who need someone to cash a check for them as that is the only way that untold millions can be accessed.............

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Old 08-14-2010, 12:00 PM   #14
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Quote:
Originally Posted by RV Roamer [Gary] View Post
The ECM (computer) in a modern diesel does a pretty good job of setting fuel mixtures and RPMs, including idle, without any assistance from the driver. I nearly always let mine handle the engine management chores.
While the modern ECM does a fantastic job of engine management (i.e. let it do all the work), my ISM ECM does NOT handle or do anything for cold high idle.

Hence, with the consistent advice of a dozen different Cummins shops, kick up the idle manually on cold starts, after oil pressure stabilization and leave up while the rig airs up then go on your merry way letting the ECM handle everything else. I've never looked for this specifically in the Cummins technical documentation, it may be in there (or not).

When a dozen techs start agreeing, I tend to start believing as well. A single tech, like what you read on the internet, is well, take it for what it's worth.
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