fast idle over rule opposes fast idle

[goinnowherefast]

Clarke Echols sent me here and said that some one of the old timers might be able to help me.

I just picked up a 66MCI5A Challeger and drove it from Oregon to my home in San Diego.

I keep reading about keeping the idle up if parked or sitting.

My main question is about the fast Idle. I was turning on the switch located on the panel to the left of the driver and nothing was happening.

When I got it home to San Diego, I looked in the manual to see where the fast Idle solenoid should be located. It wasn't there, but there was an air solenoid mounted by someone else directly in line with my throttle linkage this solenoid was mounted on the roof of the engine compartment just above the linkage 3 1/2" before the throttle linkage bolts to the twist stem which turns and increases your engine's RPM.

Anyway I had one of my boys operate the fast idle switch while I was standing at the rear of the engine and the plunger came out of this cylinder but 1 1/2" short and 1 5/8'  too high of being able to push or hold the linkage at it's end where it has a bolt through the eye at the end of the throttle linkage where it connects twist stem going down into the blower, govenor or what ever it's called. I'm used to it being called a carberator on cars.
The plunger I see is a threaded rod, so I added a small turn buckle nut with a nut to make it come out far enough to reach the eye of the linkage where it ends. I then make shifted a piece of metal which extends up 2" so the plunger will hit that and hold the idle wherever I want.
Sounded great. Except that I see that the fast Idle switch supplies air to a T in the air line and both of these solenoids: The one that I modified the linkage on and the fast Idle overrule solenoid which is stronger than the plunger which I just modified. Before I didn't have this problem because I didn't realize that the fast Idle Overrule air line had a leak at the solenoid so it didn't affect my pedal when I gave it throttle. Now it forces the stem to turn the opposite way and brings down the idle at the same time the other one is trying to hold the throttle position in place.
I thought of disconecting the overrule but I have a feeling that its there for a reason.
The bus has a Jake Brake installed, is this maybe the reason that it may have been modified?
Is this Fast Idle switch on my side panel....... there to slow my idle down by activating the Fast Idle Over rule?
It's an old bus and I don't know who to turn to for advice. I went to a company here called Rush Truck and it appeared that I already new more than they did and I don't know much as of yet.
I've read some stuff at various spots that make reference to not using the fast idle with a Jake Brake but I figured that I would just turn off the Jake before turning on the Fast Idle.

I called the Main Jake Brake company Jacobson or whatever it's called and their Detroit man said that it doesn't matter how long and at what idle a 8v71 idles. I've read to much to the contrary. Hope someone out there can help.

[Tony LEE]

The fast idle is more for keeping the revs up enough to keep the aircon running (compressor and alternator) when the bus was in passenger service. It only operates when the park brake is applied.

There are two cylinders associated with the fast idle - one operating the rack directly and the other to lock the throttle push rod so it doesn't drift and allow the engine to race.

[JackConrad]

When they installed the Jake Brake buffer switch, they probably removed your fast idle solenoid. the only other option would have been to install a Jake Brake buffer switch that has the fast idle built into it. This is about a $300-350 option.  Jack

[Utahclaimjumper]

Is there any particular reason to idle at all??  best to just shut it off when stopped for a length of time.>>>Dan

[Kristinsgrandpa]

Dan, I don't believe in excessive idling either, but some times it is necessary.

My coach air won't build up air pressure  (no brakes, etc) unless the coach is running (idling) and my transmission won't shift out of first or reverse until the temp is above 20 deg. F. So warming up the eng/trans. is necessary.

Running the engine (idling) is one of the best ways to achieve that. It won't go into any gear if under minus 20 deg. F. One of the idiosyncrasies of an HT748, probably to protect the transmission.

When my batteries went south I let the coach idle till I finished the maneuver I wanted to do.

Idling is a feature provided by the engine manufacturer to save fuel when not actually driving.

HTH, Ed.

[RJ]

Goin' Nowhere -

As others have said, the fast idle on a coach is designed to keep the RPM up to power the multi-ton HVAC system w/o drawing down the batteries.  Obviously, this is for a revenue service coach.  In an RV application, it's main function is to shorten the time necessary to build air pressure before driving off.  Diesels cool when idling, so excessive low or fast idle time creates a lot of crud, unless you've got a load on the engine (like running the HVAC).  The decision to keep or disable the fast idle on an RV coach is up to the owner.  My personal preference is to keep it, but that's only because of my industry background.

If the fast idle is wired correctly, it should not come on unless the parking brake is applied.  This is an important SAFETY built-in to the system - if it came on while driving, you immediately lose all control of your throttle - with the potential for very serious consequences.  Make sure this is not by-passed.

IMHO, the following suggestions:

1.  Remove what you've just installed/added to the fast idle/throttle linkage.  Only OEM parts should be use here - again, a SAFETY issue.

2.  If you decide to keep the fast idle application, take your coach either to Bob Roswell at HB Industries in nearby El Cajon (www.hbindustries.ws), or up to Don Fairchild in Bakersfield (www.cctskit.com) and have the fast idle/jake system repaired correctly.  Might also consider having the "rack run" at the same time, to make sure all the injectors and Jake components are adjusted properly.

3.  Put at least your city/state in your profile, so that in the future it will be easier for fellow busnuts to help with your questions.  The only way I was able to suggest the two businesses above was from the sentence where you said you brought your bus home to San Diego.  Had you not said so, would not have been able to help with the above info.

Since this was also your first post here, welcome to the MADNESS!!   And say hello to Clarke for me next time you two chat.  Tell him we miss his entertainingly educational posts here on the MAK BBS.

FWIW & HTH. . .

[goinnowherefast]

Thanx for the input.

You were right, Because I didn't have the original switch to look at, I dealt with what I could see.

I do need a Jake Brake Buffer Switch and this switch operates the Fast Idle within rather than physically by trying to move the linkage as the Fast Idle Over Rule does.

I have heard so much about Idle times and RPMs that I'm concerned about hurting my motor.

I have heard that slow idle how ever long is OK.
The person that I spoke to today to buy a rebuilt jake brake buffer switch said they sometimes let their buses run all night long because of the cold or else they won't start.
I have the original air conditioning. I've been told, don't leave let the idle drop with it running.
I read one article where the bus company has their drivers shut down even if they are going to idle for 20 seconds.

So you can see my concern. It's too much money to rebuild these engines if I'm wrong.

Getting older is saving me money by being more careful but sometimes it sure is tough trying to do the right thing with so many opposing opinions. Obviously it would be safest to not idle except at red lights. What for example do I do when I come back through the border check into the USA from Mexico. Talk about a snails pace.

I guess the question I should be asking is how long have you been driving your bus, how many rebuilds and help me please with these Idle issues.

Thanx again, you've been a great help with the fast idle Jake Brake Buffer Switch

[buswarrior]

Hello gnwf.

Run the engine when you need it.

You didn't worry about when to run your car motor, this isn't any different.

In some places, before we bought them, the bus companies left your coach, and mine, running 24/7 all winter long.

And running in summer to keep them cool.

As noted, fast idle helped the AC and alternator in a stock coach, and it is helpful to build air pressure.
Your choice to keep or discard.

You need to ask the reasons why people have their opinions, you might be shocked at the inner workings of some people's minds... completely irrational conclusions with no substantive background.

A job title or years turning a wrench does not immediately make one the source of all knowledge.

If the guy who packs parachutes never leaves the plane, he'll tell you he packs 'em right....
based on what information?

In our modern times, some fleets have realized the loss of money by burning all that fuel without sufficient payback, as well, we now have environmental regulations limiting idling in many municipalities, with fines in the hundreds of dollars for the ticket.

The trucking industry has come to accept the rule of thumb that a minute of idling does the same wear as running down the road for a minute.  Makes sence, running is running, wear is wear?

I'm betting that idling won't change the condition of your motor, because a busnut typically doesn't have the money to fuel it long enough to do so!

Start a new thread with your next concern!

happy coaching!
buswarrior