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Fast Idle
Does anyone understand how fast idle switch works and what could be wrong when it doesn’t on a 1990 XL Beaver. If you do have experience with this system and have a suggestion of what to look at, please let me know where to look. I have had several suggestions from a Prevost rep and a repair/modification facility. Still unable to find what they wanted me to check.
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13 Replies
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Jim on mine the fast idle only works when the parking brake is on and the transmission in neutral. What is your doing?
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Jim,
When I purchased my coach, the fast idle feature would not work. The problem was the pressure switch mounted on the parking brake switch was faulty. After I replaced the pressure switch, all is OK. The pressure switch is located on the air cluster that is associated with the parking brake pneumatic switch.
Good Luck,
Hector
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Greg / Hector
I have been trying to get the fast idle to work right after I start up with the transmission in neutral and the parking brake on.
Is the parking brake pressure switch located right below the barking brake button or is it remote like in the electrical bay? I tried getting to it by opening up the consol that it is mounted on, but that is proving to be difficult to get into. Did you replace to entire mechanism?
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Jim,
As I recall, the pressure switch was mounted on the parking brake pneumatic cluster. Check the switch with a meter to see if it is functioning. You should be able to work the parking brake switch and check the voltage drop across the switch.
Hector
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Tell me if your engine is a DDEC 1 or 11 and I can help you with the fast idle on a 8v92 they work different than a 60 series
good luck
Clifford
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Based on age I suspect Jim has a DDEC II.
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A 90 model could be either he can look if he has a box up front in the drivers area then it will be a DDEC1 I hope he has a 11 makes life easier lol
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The Coach Final Record says the shell was completed July 89. The injector is Detroit Diesel DDEC.
I think I found the switch in the spare tire compartment which is now occupied by two air conditioning units. Will know more tomorrow. Had to get a 1.5″ wrench to get the bumper off.
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Hot tip.
Most coaches, buses come with an lug wrench 1 1/2″ hex, the kind you put a bar through for the turning torque.
You probably already have that bumper wrench and don’t know it.
JIM
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If your parking brake switch is not the problem I will be happy to walk you through it still would like to know the DDEC series I have a friend with a Beaver his is a DDEC1
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Clifford
I am not sure if the box is in the front, but the plug in for the DDEC readout is in the lower Electrical bay below the driver. There is a small yellow air line that comes off the parking brake actuator and goes down into the spare tire area to a valve arrangement located in the center of the bus about 4 or 5′ aft of the front.. Located there, is an air switch similar to the one on the bottom of the brake valve arrangement. On the brake switch I get continuity but nothing on the valve arrangement that I think is part of the parking brake system. Couldn’t start the bus today, as we are waiting on a part and UPS is taking five days to get it from Tennessee to South Carolina.
If you would like to talk me through this, it would be most appreciated.
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Started the bus and tried the fast idle switch. It didn’t increase. Jumped the contacts on what I think is the fast idle switch. Still didn’t increase rpm. I am ready for help Clifford.
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Maybe a previous owner changed the DDEC and didn’t program it fully.
JIM
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