Fast Idle Switch

[Stu & Filo. T]

On my 1988 Crown Rear Eng I have a high Idle Switch but nothing happens when it's activated, would someone have a picture of what the module would look like on the Eng & how they work?

Thanks,, Stuart

[Stu & Filo. T]

Oh it's an 8.3 Cummings

[SassyLass]

Sorry about that, not sure what happened. It's in the Cummins forum. Try this. It worked for me.

http://www.skoolie.net/forums/f39/cu...uals-7404.html

The thread link has more details about how best to utilize this site here:
https://quickserve.cummins.com/info/index.html

[Choolbus]

OK this is what I found out. There is a big solenoid attached to an arm on the pump in front of (to the left of) the throttle arm.Switch off the arm is down(first picture), switch on the arm is pulled up.The third picture the arm is down. There is a 3wire plug you can see in the pictures. When I flip the switch it bumps the idle to 1500rpm. Let me know if this helps or if you have anymore questions.

[nat_ster]

That looks like the fuel shut off solenoid on my rear engine 8.3 Cummins.

Maybe I got my parts mixed up.

What bus is that pic from?

Nat

[Choolbus]

Maybe I have mine mixed up. I'm probably wrong. I need to observe it while someone else flips the switch. Sorry for the bad advise. I'll have to try again.

[Stu & Filo. T]

Thanks, I'm at work now won't get home until midnite I'll take a look tomorrow & try to get some good pics of what I have.

[opus]

This is the air throttle:



You are looking at the shutoff.

[Stu & Filo. T]

Ok heres what I have. Pretty confident the first pic is the air throttle second pic with push rod extended is off pos. retracted is running pos.

So is it missing another actuator for the fast idle position?

[dond]

Have one of these, used it for a while until I found out how to use the cruise control for idle speed.

[Choolbus]

These are a couple of links I have found about fast idle with air throttle
~~~~~School Bus Mechanic: Thomas Buses - Air Throttle Repair RE Throttle Linkage - School Bus Fleet Magazine Forums

[opus]

Another thought. You do know it wont work if the transmission is in gear or the parking brake is not set. Just checking.... ;) Maybe a safety switch issue.

[Choolbus]

Here is a picture under my bus of what looks like the solenoid operated dump valve like the one link I sent shows. This valve has three air lines one of which goes straight to the air throttle. Thanks allwthrrider for asking the question now I know how the fast idle works and that it wont work for my future plans.

[Stu & Filo. T]

Originally Posted by opus

Another thought. You do know it wont work if the transmission is in gear or the parking brake is not set. Just checking.... ;) Maybe a safety switch issue.

Checked & checked

[Stu & Filo. T]

Ok I do have 2 airlines off the air throttle actuator, one goes to this and the other goes to this,

The first one looks like a solenoid with a dump line & another line that looks like it goes to the front of the bus,

The other is a fitting into the transmission with 2 lines into that it also looks like the red line off the fitting into the trans goes to the front of the bus.

ALSO there's a capped off airline hanging right next to it.

It appears the capped line goes to the front of the bus also

[Choolbus]

OK I am going to summarize what I think is supposed to go on with your fast idle from what I have read. Air is supplied to the throttle pedal through the transmission air modulator to the air throttle. The Air Throttle has a spring that sets at fast idle. After start up air goes to the Air Throttle to set it at normal idle. Flipping on the Fast Idle Switch dumps the air in the Air Throttle so the spring can pull it into fast idle. I didn't
read in my looking around what opus said about different safety switches but I'm sure he's right. Now this is from what I read not my own knowledge but it makes sense to me. One thing I did notice is that in your pictures and your writing is that your air lines are red. Someone in the past must have done some repair with what ever air line color was available. The main concern is the mixing of the two air systems(not a good thing) red is suppose to be only for the emergency braking system. If there is some mixing of the two systems it could explain your issue.