King Control: Throttle and Cruise Control Issues

Today when I check oil, etc and did a look around and found one of our two throttle return springs hanging on one end of the spring as the other end had broken off.

I made several replacement springs a while ago as others have broken.  So I had to get them out of my important Foretravel spare parts box.  I decided to replace both at this time, even though one was still good.

Our mechanical C Cummins engine has two throttle return springs that are mounted next to each other, probably more for safety redundancy than offering more spring return strength. Each of the two springs has its own top & bottom mounting holes. 

Years ago, I found OEM spring replacements impossible to find and have been buying hardware springs and cutting them down to correct length.

In a hardware store, I looked for springs of similar diameter & spring steel thickness, trying many until I found some with the same pull resistance and spring return feel, as original spring.

With a metal cutter, I shortened the new spring a couple of turns longer than the original. With two pliers I gently make a ring loop with the last spring end loop.  This has worked just fine for the 6 or so springs I have made.  None of the loops have broken while I bent them 90 degrees.

The label on the springs I mounted today is: Hillman, Cincinnati OH 45321 UPC 0-08236-80114-9 Made in Taiwan HPM# 07828 #543016 Extension 0.44” x 10.25” x 040” 11.10mm x 260.35mm x 1.05mm Safe working load: 1.4 lbs

Our 1997 U270 uses a ‘fly by wire’ throttle where the throttle rotates a resistance control that tells the throttle controller located in the back corner of the engine compartment on the curbside what the throttle position is. This controller was developed by King Control, the same guy later developed the King Dome satellite antenna.

The King throttle control was obsoleted by electronic engines and one of the lead King Control employees bought the throttle/cruise control business and runs it under a different business name. He is very helpful and knowledgeable and is located in the Minneapolis, MN area. He has worked on our controller and I recommend anyone who has a King Control and is in the area to stop at the plant.

Prior to the use of King Control, throttles were controlled by an air cylinder. Motorhome manufacturers about 1995 asked King who was supplying the cruise control if they could create an electric throttle for the Cummins engine. This included Foretravel, Monaco, Country Coach, etc.

But within about 4 years, Cummins came out with electronic computerized engines that included throttle and cruise controls and King was no longer needed for new coaches. But there was and still is a need for cruise controls to be added to older big trucks, so King still has a potential market. And is also servicing their short-lived motorhome OEM installations.

King Control must ‘see’ working rear brake light bulbs to allow normal RPMs, otherwise, King will keep throttle from retracting very much. This safety circuit is in place to be sure that an activated brake lamp circuit will be able to turn King Cruise Control off.  

 There are two air pressure switches mounted in the left forward compartment on the forward top metal wall. The air pressure switches close a 12-volt switch to turn on brake lamps. The two switches monitor front and rear air brake activation.

Also, our King Control wiring has been modified by running a ground wire directly to start battery to ensure a secure ground connection.

The cruise control relies on the brake light circuit to know when coach brakes are applied, so it can safely turn off the cruise control when brakes are applied. To be sure the brake light circuit can be ‘seen’ by the cruise/throttle control (which is the same circuit board) the controller must see a resistance through the brake light bulb to ground. If the brakes lights appear to be burned out or otherwise malfunctioning the King Control will only allow about 5 to 10 MPH of throttle control.

If everything is ok with brake lights, the King Control can be malfunctioning and new board can be ordered from King Control. Board is not hard to install, but a new gasket must be installed to keep the cover sealed from moisture.

There have been known problems with circuit board inside King box, that are fixed with a control board swap out. King box is mounted curbside rear of the engine on frame. Easy to locate as it has a cable to engine throttle linkage. The box is rectangular and has a round cylinder sticking out of one end, which is servo-motor. Easy to see from the rear or open bed. While looking, check that you have dual throttle return springs mounted vertically on the curbside of the engine.

Basically King Control is electronic throttle control. The only thing it does is wind up a cable that is attached to the engine throttle. King also tells transmission when the throttle pedal is an idle position and at the wide-open position.

The throttle pedal has a variable resistor that indicates electrically the throttle pedal position. Commonly called ‘drive by wire’. King Control original design was just cruise control, which uses vehicle speed info to run the engine throttle. And is still sold as a cruise control for trucks, etc.

King was approached to see if he could add throttle pedal control in the ’90s, to replace air throttle pedal which is the main alternative to fly-by-wire. Of course, later electronic engines obsoleted add-on cruise and throttle pedal management.

When a throttle does not work, a temporary workaround has been reported that is being called ‘fly by rope’. The bed is raised an inch with a board placed to keep the bed up. A rope is attached at the engine lever that increases fuel flow, which was normally moved by the King Control. The other end of the rope is upfront by the dash and one drive by pulling forward on the rope. Normal throttle springs pull the throttle back to the idle position.

By the way, these two throttle springs sometimes break and this can cause runaway engine RPM. Check that both springs are in place. Replacement springs can be made from regular hardware store matching springs. Better to have a spare or replace them before one break. by Barry and Cindy 1997 U270 36′ 12/07

I had a good discussion with Steve at King Cruise Control (952-942-9644) this afternoon.  Just as Barry (and Bill W) indicated, most of my incidents may be explained by an intermittent loss of the King Control ground through the air actuated brake pressure switch terminations to the brake light circuits to ground. 

Based on the nature of the corrosion that I have on our coach, I strongly believe that my corrosion is primarily related to the salt residue and the liquid chlorides used on the roadways for snow and ice control vs. any proximity to bodies of saltwater.  I know that early on in its life and more recently when headed south in the late fall; our coach has been severely exposed to liquid chloride treatments, some small amounts in New England, but most extensively in TN and NC.  On several occasions, our best-laid plans to avoid such winter weather indignities have gone astray and the liquid chloride is incredibly invasive and damaging.  My brake pressure switches, located in the open compartment forward of the street side front wheel, appear to be highly corroded and I didn’t realize that the King Controls must see a reliable ground through these switch terminations and all the way back through the brake light filaments to ground in order to function properly.


The King Control/Cruise Control (KC/CC) will interrupt CC when it senses 12Vdc in your Brake light circuit.

The 12Vdc is/should be sensed downstream of the two pressure switches mounted up high on your street-side, forward-most compartment, front panel.

Those pressure switches monitor your front and rear air brake system pressures.  As your brake treadle is depressed, these switches actuate, at their set points, allowing 12Vdc to pass to the brake light filament wires.  The KC/CC also has a sensing wire that lands on one or both of these switches, which provides the ground path through the brake light filaments, that the KC/CC must have in order to allow throttle responses > 1500RPM.

These sealed pressure switches are pretty reliable, but it is possible that one or both have shifted in setpoint or may be otherwise unreliable (contacts may be arced and unreliable).  The switches are not adjustable and can’t be disassembled.

Because these switches are located in an open, “wet” compartment, the switch terminals can become corroded or become loose and one or more unreliable circuits for the KC/CC (FT also common up to several sets of wires on some of these terminals, which leads to reliability issues in unprotected environments).

Then I would take the wires off, one terminal at a time, clean, lube and re-land them and see if/where it makes your problem go away.  Then you may have found it.  Soldering any common wire sets together, for each terminal, is one way to reduce future aggravations. If that doesn’t do it, but you can see with a voltmeter that it takes too much treadle pressure to actuate one or both of the two pressure switches, then you have pressure switches to replace.

I also didn’t know that King would refurbish units.  When our coach was about 4 years old, I replaced what appeared to be a perfectly good King Control Unit because the throttle cable was beginning to fray at the throttle block termination spring.  At the time, FT Nac advised me that there was no repair or refurbishment allowed on the King units (by FT, King or others) due to liability issues.  I saved the original unit, intending to verify that fact, but never did.  Steve tells me that barring other issues; the repair and refurbishment should be $75 to $100.  So the spare unit is on its way to King in MN this afternoon. Neal Pillsbury 98 U270 36 8/20/09

I solved my throttle issues when I installed an air throttle, I still use the King control for cruise only. Bill Willett 97 U270 8/20/09

Steve Boller, owner 22250 Glyview Trail Faribault MN 55021 507-334-0250 651-398-5555 emergency only (cell phone)

This throttle control/cruise control is used on mid-to-late 90’s mechanical Cummins engines. The newer electronic-control engines made these units obsolete. Steve can fix them.

And the King Control electronic cruise control makes a great refit in the early 1990’s coaches with the obsolete Bendix cruise as well. You can use the same driver control, wire from front to back, etc. It makes for pretty easy installation and is more precise than the old Bendix unit.

Throttle Springs
Get it Home Kit
Throttle Cable- bracket
King Control
Air Throttle
TPS Sensor

Photos by Bill W.

While driving, we suddenly lost engine acceleration, and after bringing us safely to the side of the road, I found a throttle bracket part broken in two.

We have King Throttle Control which pulls on a cable that is attached to the bracket that broke, so we had no throttle.

We were able to drive to the next town where we could figure out what to do next, by pulling up on a string we attached to the half of the throttle bracket still attached to the injector pump.  Cindy drove and I made us go from the side of the bed.  Could not pull the string forward from the dash area, because the broken part had to be pulled up toward the bedroom ceiling.

The local hardware store had no parts to help us but did offer their bench vise so we could fashion a replacement part from a spare piece flat aluminum we were carrying.  Our new temporary part worked out so well, we decided to make it a permanent part and for the last four months, we are better than new.  The original part had a large hole that was so off-center, one side had too little metal, causing the failure.

I am sure every throttle linkage problem is different, so there is no set way to run a rope from the front to the engine. We could have put an eyebolt under the bed to make a forward pull, a pull up on the linkage, so one person could move the coach. by Barry and Cindy 1997 U270 36′

Our Cummins C8.3-325 engine has a throttle bracket that is pulled in one way by King Control cable to increase RPM and two springs in the other way when the accelerator pedal is not being pressed.

Last year the throttle bracket broke into two pieces while driving up a hill.  We previously posted on Foreforums how we made a replacement bracket in a hardware store parking lot using a spare piece of aluminum we carried.

This is a follow-up posting explaining a design problem with the original OEM bracket that may affect others.

The two springs, hooked into two small separate holes in the bracket, are at all times exerting a pull on the bracket to return and keep the throttle at idle position.  Springs pulling on the original steel bracket for 15 years wore away both holes and may have eventually released the springs, maybe preventing throttle from returning to idle.  We found the worn holes when our bracket broke in another place.

We had a concern that the springs would wear the new bracket and maybe much sooner because the replacement was made from aluminum, which is softer than steel.  Today we took the aluminum bracket off and found some minimal wear and decided to modify our throttle bracket by using eye-bolts to attach the springs.  Eye-bolts are made of steel and are round where the springs attach.  Maybe because the springs can move in the ‘eye’ they will not cause a wear point.  Photos show the worn original bracket and our new modifications

Holes Wear