CDS 4.8 isn't running at correct rpm

Bryce C · Thursday at 5:17 PM

My Hydramaster CDS 4.8 starts at around 1100 rpm on the high setting, and slowly loses rpm and drops to around 600 rpm Weak vacuum, water pump has weak pressure, and my local truckmount service people say they won't work on it. The don't service anything on the engine side of pto setups.

It is a 2013 and doesn't have the adjustable vacuum pods like I read some older models have. There is an electrical pod under the dash but I don't know if anything is adjustable on it. The local truckmount service folks checked for vacuum leaks in the lines that may affect this and didn't find any. They think it is electrical.

I'm waiting to hear back from a friend who is a Hydramaster tech I met at MF this year. For now, do any folks with experience with these CDS systems have any thoughts?

Bryce C · Thursday at 5:19 PM

Based on what they saw, the local truckmount service folks think the tm will be in great shape once this engine rpm issue gets resolved... The van is a 2500 Express

I set out to buy this thing in April, couldn't pick it up until May because they rebuilt the van engine, and here I am in June and I still haven't cleaned with this thing once

Bryce C · Thursday at 5:41 PM

Well, looks like the previous owner just spliced in the electrical rather than getting the proper harness. My friend at Hydramaster just helped me realize that. He's ordering me the right harness and will talk me through installing it when it comes in. Things are looking up. Maybe..!

Dwain Ray · Thursday at 10:28 PM

Bryce C said:
Well, looks like the previous owner just spliced in the electrical rather than getting the proper harness. My friend at Hydramaster just helped me realize that. He's ordering me the right harness and will talk me through installing it when it comes in. Things are looking up. Maybe..! View attachment 131308 View attachment 131307

Heres the installation/ operation/ troubleshooting for that throttle controller hope it helps. I had to screen shot it. I have it as a pdf file and i don't know how to send it if you have any questions i built my machine from scratch and used this same throttle controller and im familiar with it

Dwain Ray · Thursday at 10:51 PM

You have 3 leds not on in picture or are flashing and show as off. What are is the description marked for each light?

Bryce C · 2025-06-13T21:08:19-0400

Dwain Ray said:
You have 3 leds not on in picture or are flashing and show as off. What are is the description marked for each light?

Thanks Dwain! The 7 led lights that are on, they flash on and off together in sync continuously when the machine is powered up. I just took a pic at a moment with them flashing on. The 3 lights that are not on at all, and do no flash on, are "rpm1", "rpm2", and "chrg".

The instruction manual you kindly posted pics of doesn't list my 2013 Chevy 2500 Express as a supported make/model...

What do you make of the hack splice without the appropriate 16 pin harness?

Dwain Ray · 2025-06-13T21:32:37-0400

If spliced to the right post, it shouldn't be a problem the controller wiring harness from the factory comes with a obd2 plug on it and you plug it into the vans port. I didn't like that because inorder to diagnose using the port you had to first unplug the throttle controller. I used an obd2 splitter which does the same as tapping the back except its plug n play. You remove your vans obd2 wiring from dash and plug it into the splitter mount 1 end of the splitter to the dash and plug the throttle controller into the remaining port allowing me to use the obd2 port and throttle controller simultaneously but wiring to the back does the same. But because I was doing this to a new van i didn't want to deal with any potential warranty issues

Dwain Ray · 2025-06-13T21:38:51-0400

If any of the lights are flashing on the throttle controller thats an indication of a problem the lights are supposed to be on solid are you aware that controller is connected to the emergency brake??? If the transmission is not in park and the emergency brake is not engaged the throttle controller will not work ( safty features)

Bryce C · 2025-06-13T21:43:55-0400

Dwain Ray said:
If any of the lights are flashing on the throttle controller thats an indication of a problem the lights are supposed to be on solid are you aware that controller is connected to the emergency brake??? If the transmission is not in park and the emergency brake is not engaged the throttle controller will not work ( safty features)

Yes the emergency brake was engaged when I was testing it out. I was under the impression the clutch drive wouldn't even engage if the emergency brake isn't engaged...

Dwain Ray · 2025-06-13T21:59:58-0400

Im not sure of any of that im really not familiar with your machine. my machine is all custom built with off the shelf parts from 5 different manufacturers one of which is the same model throttle controller as you have i can clutch in and out without the emergency brake. My system has a master switch on the dash that powers up and shuts down everything machine,wastepump, waterpond lighting, everything