Hi all,
Like the title says, the fast idle just stopped working on my 1981 MCI MC9 (8V-71N). I have the Spicer 4-speed manual transmission. I was moving it in the driveway jockeying it around, and when I went to park it, the fast idle wouldn't kick in. It's never done this, so I'm seeking advice for the first places to look. Here's my plan...
Start with the electrical and see if the Skinner valve is seeing voltage. If it's not, then I'll trace that down. Looking at the schematic, it looks like it could be the parking brake switch, or the neutral relay. (Is there even a neutral indicator on a manual transmission or is that something only for an auto transmission?)
If the Skinner valve is seeing voltage, then I'm thinking it is probably an air problem. Anyone here know of an obvious place I should start looking that I'm not thinking about?
Thanks in advance for any assistance. I'll post what I find out when I start digging. It stopped working so suddenly I'm thinking its got to be electrical.
Mine stopped working back in the summer. It was the parking brake switch.
I could be wrong but make sure the parking brake is set. I don't think fast idle will work otherwise. j
Quote from: challenger440 on September 29, 2014, 06:51:57 PM
I could be wrong but make sure the parking brake is set. I don't think fast idle will work otherwise. j
That is correct.
Ahhhh, Good to know! My fast idle hasn't worked since I bought it - and the park brake switch was unhooked also. Guess Ill get a new switch and see if that fixes it. While we are on the subject, what do you all use your fast idle switches for?
Thanks for the replies guys. I did have the parking brake engaged, so it very possibly could be the switch. This gives me a good place to start, which is exactly what I was looking for. I haven't had a chance to take a look yet to see if the Skinner valve is seeing voltage.
Newbob - I've got a 4000 watt inverter that I'm running two roof airs off of when I'm going down the road. If I stop for a minute or two I flip the switch just to keep the RPM's up a little so the A/C isn't drawing as much from the batteries. I also use it if I'm going to be idling for a few minutes to keep the oil pressure up. From what I understand, none of this is really necessary in the case of a bus used as an RV, but it can't hurt I guess. It may burn a little more fuel, but I don't run mine long enough to make much of a difference. If I'm idling longer than a few minutes, I just turn it off. The real reason for my desire to fix it is that if I'm going to keep it, I'd just like for it to work. Thanks again. When I get to it later this week I'll let you know what I find.
I still have 2 figure out my fast idle . Only thing really wrong with my bus. I can turn it on while driving and cruise 65 on freeway . Of course I dont ! It was while troubleshooting .. I'm glad now I know it should only work while parked ... But at park it will runaway at ungodly Rpms.... I am going to address in future .. Thanks for the additional info ... Lvrbus gave me some ideas as to problem ... Just need to get back at it but using bus every wknd ....good luck!
OK, so here's the update. Since LuckyChow stated that his switch had gone bad, I decided to start there. The emergency brake air switch is located in the spare tire compartment above the removable fiberglass panel. I clipped a jumper across the switch closest to the front of the bus, flipped the fast idle switch inside, and voila, it worked. Bad switch. Here's where I need a little help...
I can always call Luke and get the right thing, but I wanted to see if it's available locally first. Does anyone have a part number for the emergency brake air switch? Mine has the following stamped on it, and nobody is able to cross reference it with anything. "60 BREAK 5653700351"
Just as a data point, there are three air switches located in the spare tire compartment of my 1981 MC9. One is for the brake lights as applied by the treadle valve. One is the switch that activates the brake lights when the parking/emergency brake is on, and one is for the fast idle.
Those are just S3 or S4 stop light switches should be easy to find locally, they may look different but any air switch will work if it closes under pressure and has 2 terminals I think I bought a Velvac for under 10 bucks at CarQuest
Ah, thank you Clifford. Exactly what I was looking for. I'll check that out.
I thought of something else that may be helpful to some one who owns a 9. While I was troubleshooting, I put a jumper across the terminals of the bad air switch in question. It enabled me to flip the switch and power up the fast idle, but because it wasn't being influenced by pressure, it also enabled fast idle to run with the parking brake off. If you're one of those folks who says their fast idle will operate even with the parking brake off, your switch might be stuck in the closed position. Just a thought.
In hindsight this all makes perfect senses, and everything is operating like it's supposed to, but I hadn't thought it all the way through that if the switch is stuck closed, fast idle will operate with the parking brake off - which on my bus is a disaster waiting to happen. When my fast idle is engaged, you lose all throttle input. This is why they wired it to the parking brake in the first place - so the bus has to be stopped so you can use it.
I hope this is helpful to someone. I like to add stuff like this to the board so folks can find something in the future that might be useful. I'll let you know what switch I go with.
So I thought I'd post what finally happened with my fast idle for posterity...
After troubleshooting with my handy alligator-clip jumper wire, I was able to figure out that the problem with my fast idle was the pressure switch (located in the spare tire compartment.) Despite some good information from the board here, my local parts guys weren't able to find one. I live in a pretty remote location, and they basically looked at me like I was from Mars for even asking - even though I had the part with intact part number in my hand. Oh well, no worries. Living here has taught me well how to source things online.
I found what I was looking for at eGuages.com (not a plug - just information.) It's a VDO Pressure switch, part number 230-660, that can be wired normally open, or normally closed. Since I wasn't exactly sure which I needed, I ordered one (about $35), thinking that I wouldn't have to wait another 3-4 days if I ordered the wrong thing. Wired it up last night in the normally closed position, and my fast idle now works perfectly. Hope this helps.
GReat info - thank you for sharing!!
Adding to the thread; I have an intermitent high idle on my 871. Flip the switch and the piston pops out that keeps you from operating the throttle pedal. And the air pressure gauge starts to drop but the engine doesn't always hop up on high idle.
Is there an air cylinder reaching into the governor body that actually speeds up the idle? Maybe it's worn out and leaking and causing my intermitent symptom.
Fred
The Skinner valve that actuates the fast idle operates two air cylinders - one locks the speed control lever and the other is on the left hand side of the governor (as you are facing it). It is also the buffer screw. When the air cylinder gets air it pushes a rod with a spring into play that pushes on the idle speed control inside the governor (the same one that the buffer spring very lightly assists to stabilize the idle) and adds the strength of the fast idle spring to the idle spring. That is what gives you the fast idle. You should not be able to see the air pressure gauge change when you click on fast idle, virtually no air is actually used (call it about a cubic inch of air to actuate both cylinders). Trace the air line that goes to the air cylinder that locks the speed control lever - it should have a tee connection and one line will go to the skinner valve and one line will go to the fast idle cylinder on the governor.
This is all if you have the same fast idle setup on your MCI that I have on my MCI, of course...
If you go poking around with the fast idle cylinder remember that it is also the buffer screw and as such must be adjusted precisely and carefully. Too far out, and your idle will not be stabilized. Too far in and the engine can run away.
Brian
Hey Fred,
Given your setup is the same as Brian's and mine, I think you're on the right track. The cylinder that controls the governor (or the air line) must be leaking like crazy to make the air gauge drop. Like Brian stated, it hardly uses any air at all. Good luck. Intermittent stuff makes me crazy.
Yah that is the way mine is set up Brian. Sometimes it works perfectly. But the times it doesn't work it sucks the air gauge down noticeably. Can I activate the high idle with the main switch on but the engine not running ? For testing purposes? Isn't there a relay that is activated once the engine is running that controls things like that?
Fred
On my schematic, MC-5C and yours should be the same, power is fed from the master switch on the dash to the parking brake switch (I think above the spare tire) to the fast idle switch on the driver's side switch panel to the Skinner valve beside the rear control box (normally closed, opens and passes air with power on), which opens and feeds air to the fast idle cylinder. You should be able to jump power to the skinner valve inside the remote control box (inside the box where the rear start switches are), you can trace the wire to the valve to a stud in there. If they are labeled it might be stud 10 on the horizontal block. You might also be able to handily jump power to it using stud 22 in the engine compartment electrical bay. You will obviously need air pressure for anything to work. If it's leaking it could obviously be the skinner valve or either of the two air cylinders or a hose. If it's electrically intermittent I might start with the parking brake switch. In your case it would be obvious to suspect the fast idle cylinder but if something else is leaking prior to it, it might just not be getting sufficient air to overcome it's return spring.
Brian
I wanted to reply to this because my bus hasn't had a working fast idle since I purchased it. I think this is a good description for problem solving fast idle.
Summary: As I understand it there are basically 4 potential problems for fast isle not working:
1- The switch itself is dead / malfunctioning
2- The parking brake solenoid is not working / not getting voltage
3- One or both of the skinner valves is broken / clogged / inoperable
4- The pneumatic cylinder which actuates the physical throttle lever is not working.
Please chime in if I am wrong or mislead.
Starting front front to back. I get 27V from the post to ground regardless of switch/ ign position on the #40 post (The little metal tag on the switch wire has a 40 stamped on it). Which solenoid should I be diagnosing. The one with ground to frame is first in line from front to back, then the red air line solenoid, then there are 2-3 more near the back wall of the spare tire compartment. I'm thinking its the second option but I don't know what I'm look at?
Bird
You have a picture of the fast idle cylinder on the governor housing ? if you have Jakes could be there is not a fast idle on the engine
Ok, this was my goal today, so I've been crawling under the spare tire comp 10+ times already. I happen to just notice the solenoid against the back wall had a wire tag. I cleaned it off and sure enough, there is was, 40. Had to be it. I started the bus, let is air up and crossed the pins with a screwdriver, BINGO, it kicked up to 1000 RPMs, or it kicked up regardless, I could see the tack.
Here is a picture for ref, I'm excited and I hope this helps someone! It is paired with another solenoid back to back and leads over to a square housing and back to the back.
J
Just for reference, the fast idle air system has two separate air cylinders. One locks the throttle lever closed, the other works on the buffer inside the governor to actually raise the idle. Good job finding the parking brake air switch.
Brian
I was excited to start the bus this weekend to see if my new VDO switch would solve my problems. KINDA. I had to rewire the switch to Normally Closed (NC). This mean the switch itself isn't getting any air, I thought it was funny when I unscrewed the old switch that no air escaped, this is a whole new problem, any suggestions? Maybe the E-Brake valve stuck?
By wiring NC I was able to override the switch and get the Fast Idle to actuate. First problem was the stop cylinder leaked like crazy. I ordered a new gasket. The actual fast idle was super erratic giving RPMs all over the board. I'm assuming the way the close air cylinder is designed that the air pushes that cylinder and alows pressure to stay constant, but because it was leaking the actual govenor valve was unable to maintain a steady pressure.
I took the cylinder off, took it apart and cleaned it. I ordered a new seal for $6 - Measured 18mm ID X 25mm OD X 5mm D(maybe 5.5) - See pictures: https://www.ebay.com/itm/162011307472 (https://www.ebay.com/itm/162011307472)
I used metric because we are the only country that uses the imperial system and I ordered it online. Oh, the seal is called a U-Cup!
J