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Author Topic: Fast Idle  (Read 1915 times)
rambunctious
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« on: April 21, 2006, 08:00:49 PM »

Can I use the engine oil pressure to run the fast idle on my 8V92?  i currently hold the throttle down until the air pressure builds up enough to work the fast idle.  I'm going to install an air throttle so this won't work.  It takes a loooong time to build up air pressure with out running the RPM up. 
Thanks in advance.
 Huh
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Don Fairchild
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« Reply #1 on: April 22, 2006, 12:41:48 PM »

you dont want to use oil to run the fast idle. I would look for air leaks, a kink in the air line, a worn high idle assy. or a worn air compressor as the culpret. On my eagle as well as the MCI's I work on it only takes about 30 to 45 seconds for the fast idle to start working on first start up. On my eagle I start the engine and turn on the fast idle and before I can get out of the coach the high idle starts working.

Hope this helps.

Don
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FloridaCliff
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« Reply #2 on: April 22, 2006, 02:28:06 PM »

Put on the shop air and check for leaks.

Its hard to hear most leaks over the roar of the engine.

I have almost completed all the leak repairs on mine and what a difference.
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1975 GMC  P8M4905A-1160    North Central Florida

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NJT5047
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« Reply #3 on: April 22, 2006, 08:10:59 PM »

Repairing air leaks is a good idea, but it may be difficult and time consuming to find them all...and leaks can be very expensive to eliminate.   There's a quick-fix for your problem. 
Have you considered adding a small electric air compressor to your coach so that it airs up before cranking?  Or, if parked inside or near a building with an air supply, house air umbilicus.  An electric onboard compressor will also make for fast exits when leaving campgrounds.   
Keeps air system charged when camping on a pole.   If you use airbags for leveling, they stay inflated.   
If the compressor is large enough, could add redundency, albeit temporary,  to engine compressor. 
Best, JR
« Last Edit: April 22, 2006, 08:16:34 PM by NJT5047 » Logged

JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.”

Ayn Rand
El-Sonador
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« Reply #4 on: April 23, 2006, 04:59:26 AM »

Can I use the engine oil pressure to run the fast idle on my 8V92?  i currently hold the throttle down until the air pressure builds up enough to work the fast idle.  I'm going to install an air throttle so this won't work.  It takes a loooong time to build up air pressure with out running the RPM up.  Thanks in advance. Huh

Don't do it...

I agree with the other replies here, plus having fast idle kicking in before your air is up means that you are probably running with lose belts as the air going to those slack adjusters have not fully set the belt tensions yet. [I'm still having Belt-Phobia... Smiley]

Like the others have said, Air-Up your bus using a "quiet" off-bus source, like shop air and get at those leaks, one at a time, and don't stop until you have managed to contain as many as possible. Overriding your air system with an on-board auxiliary air compressor is not a bad idea either, I installed one, but if you are leaking, that little aux unit will have trouble keeping up and will run often... You will find, for the most part, that many leaks can be fixed very easily, only a few may be more involved...

It will make the world of difference...

Steve
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DrDave
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« Reply #5 on: April 23, 2006, 09:53:18 AM »

Fast idling a cold detroit is probably not very good for the engine. Undecided

Find and fix the air leaks first, Then things will go much better for you and you won't need
the fast idle to build air pressure.
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NJT5047
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« Reply #6 on: April 23, 2006, 04:58:49 PM »

Don't know if fast idling a DD is good or bad.  My DDEC 6V92 will fast idle from the time it's started.   I don't add fast idle until oil pressure is up, and it runs for a half minute.   If you used an onboard compressor, it would typically only be used to air up prior to driving the bus.   No need for air while parked unless it keeps leaking airbags up for leveling. 
Fixing air leaks may be cheap, and it may be quite expensive.  Most individual valves, lines etc, are not expensive.  Airbags may set you back a little.  I've replaced the drive axle and steering axle air bags on my MC9.   Still will leak down, but since the airbags can be isolated, the coach appears to be aired up for months.   Every air regulator on the bus leaked.  I've replaced some, others will have to wait.   Replaced one wiper motor, and all wiper controls.  Even the windshield washer valve leaked air. 
The leaks can be  repaired, but it ain't necessarily easy or cheap. 
DrDave is correct, the leaks should be fixed. 
Good luck, JR
BTW, don't think fast idle with low air will hurt belts that don't have other problems such as misalignment or excessive wear.  The AC won't work either way until the low air relay allows. 

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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.”

Ayn Rand
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