In the interest of continued learning, this might help you out of a jamb

I was part of an issue with a RPM Throttle  problem on a Putzmeister Pump mounted on a  MR688S

The cruse control worked in Drive mode, but when in PTO No RPM function worked.

I tested the circuit from the Putzmeister system to the Mack VECU and I had all the needed function or so I thought.

I had PTO signal to VECU   VJ1-6-0.8

I had RPM + and – function. VJ1-8-0.8 , VJ1-7-0.8

What I didn’t have and didn’t know about was that I also needed a signal to the VECU     VJ1-10 telling the VECU the Park Brake was set.

I learned that on the back of the Park Brake switch there is 3 air switches. From the valve out the first switch is power to the VECU (VJ1-10) to indicate the Parking Brake is set, The second switch is power to Pin 2 of the Pump/Drive Switch to allow PTO function. The 3^rd switch is power to a light on the Dash to indicate the Park Brake is on.

I have always known the purpose of the 2^nd switch but the other 2 is new to me.

These 3 switches are normally closed so with the Parke Brake set power goes through them, when the Park Brakes are released the switches open and no PTO or RPM functions happen.

These wires at all 3 of the switches are spade connectors, over time they can get loose and cause an intermittent issue so it is a good thing to find them and ensure they are tight and see how it works before you have an issue on a jobsite. While you are in there if you look toward the PTO switch the back has 12 screw terminals, this is a good time to take a screwdriver and ensure all 12 are tight.

To access this valve you will need to remove the doghouse cover, remove the screws all around the entire cover and lift it up to expose the back side of the valve, just removing the covers that allow access to the fuses wont be enough.

There are a lot of wires in there but just be careful and cautious and take your time it isn’t so bad.

During the issue the foot pedal was still working so we could increase the RPM, but this has its hazards because you can over speed the pumps, so take caution as to just putting a stick or rock on the foot pedal it can get you by but can also cause other problems later.

As always please call the Putzmeister CSG or Mack service if you have issues you cant fix, but there is a lot you can do to be proactive yourself on your machine, I also think this is similar to other Brand units, but call the service dept for the unit you are working on to be sure.

Please jump in to this and add to it, I appologise for the blotchy wording in the boxes. Dont know what happened to the transfer.

I hope this helps

Great info Traveltech I would also like to add if your rpm is not working correctly to check the switch on the clutch right behind the steereing column above the clutch pedal.It could also be the rpm problem before ripping a dog house apart at 3:00 am in the morning. Every one be safe.

i had a issue where the lever that tells your cruise and engine that the clutch is being engaged slipped down behind tab and i didnt have any throttle at 3 in the morning not until about 1/2 way through 800 yds did i figure it out

You are both correct, 2 other things are the foot brake switch and the "Johnny bar" or Trailer brake handle. either of them interrupt the Cruse control. Thanks for adding.

I would like add the problem I experienced: one of the two air switches at the brake pedal (underneath the cab) was shorted out, and every time the rock valve shifted and shook the truck, it closed the circuit and for a splitsecond the brake light came on; this in return made the VECU think that somebody is pushing down the brake pedal, which caused the truck to idle down; there are 2x switches, always replace both at the same time

Very nice, thanks for the tips. Yes one time my idle didn't work on a 42 M I had, with three trucks lined up and a moody big time contractor. Why? because I figured out I was in heavy mud and after moving the brake wasn't set. Da..yeah but simple fixed don't always come easy.

Oh! the amount of time it takes to figure this stuff out, Thanks Travel Teck