Goddy454 Posted November 12, 2023 Share Posted November 12, 2023 I have a gu813 with a manual trans. The truck is a cesspool pumper. The PTO operates fine, kicks in and out with no problems through the factory PTO switch setup. The idle run speed is ramped up through the cruise control and is run at 1200 RPM. The problem I am having is that at random times the ramp up just stops and engine goes back to idle. It will restart by pressing the accel down. The switch was replaced and that did not solve the problem. The PTO itself does not shut down, just looses the speed. I've timed how long it ramps up before shutting down and there is no specific length, always different. There are no codes that I believe to be related to the issue. Any ideas anyone? Thank You Quote Link to comment Share on other sites More sharing options...
JoeH Posted November 12, 2023 Share Posted November 12, 2023 I have a 2003 MR688S that does the same thing, but it's accompanied by a trans code (Allison automatic) the code stays active and won't let the cruise throttle control "ramp up" for the PTO work until you put the truck in drive and go fast enough for the torque converter clutch to lock up. (5-10mph) restarting truck doesn't work. Gotta lock up the TCC. Quote Link to comment Share on other sites More sharing options...
JoeH Posted November 12, 2023 Share Posted November 12, 2023 (edited) All I can think is the truck senses a component in the trans spinning from the inertia of the engine revved up and it triggers a code because in neutral/parked the trans sensors shouldn't sense any movement. Edited November 12, 2023 by JoeH Quote Link to comment Share on other sites More sharing options...
JoeH Posted November 12, 2023 Share Posted November 12, 2023 Annoying on a truck that runs a manufacturing process that requires multiple different materials to be set at specific flow rates in order to make a good product. It throws the flow rate ratios off, and we either have to adjust them or drive the truck far enough (50 yards?) And fast enough (5-10 mph) to satisfy the computer. Quote Link to comment Share on other sites More sharing options...
Goddy454 Posted November 12, 2023 Author Share Posted November 12, 2023 Thats a possibility I will look into, I think what I might have to do is clear all my BS codes and run the PTO and see if anything triggers. I do have a park brake switch code, but inactive, VECU data link code, inactive too and a coolant level code, also inactive. All these codes though only show 1 count so I didn't look into these yet. Time to play. Thanks Quote Link to comment Share on other sites More sharing options...
JoeH Posted November 12, 2023 Share Posted November 12, 2023 You're also dealing with a manual trans you said, so you have different sensor inputs and outputs. And you have a GU813 which is probably an mp series engine whereas I have a vmac III etech engine. Quote Link to comment Share on other sites More sharing options...
Goddy454 Posted November 14, 2023 Author Share Posted November 14, 2023 OK here is what I found, while looking more the speed cut out then would not ramp up at all. That's when I noticed the park brake lamp was not illuminated. I am going to replace the switch first but I think I might have an issue with the park brake valve or an air issue in that circuit. Something just doesn't sound normal when I apply and release the spring brakes. Figured I would give you an update and thanks. Will let you know what it was for sure when I find out. Quote Link to comment Share on other sites More sharing options...
Goddy454 Posted November 14, 2023 Author Share Posted November 14, 2023 Also the switch is not throwing any codes like I have had with others which is also leading me to an air issue. Quote Link to comment Share on other sites More sharing options...
Goddy454 Posted November 16, 2023 Author Share Posted November 16, 2023 Replaced the switch and so far no probs. Thanks 1 Quote Link to comment Share on other sites More sharing options...
JoeH Posted November 17, 2023 Share Posted November 17, 2023 I know heating oil trucks are set up that engaging the PTO sets the parking brake. In the age of computers, I suppose anything is possible. I could see the CPU thinking the truck is not parked could affect the ramp up. Quote Link to comment Share on other sites More sharing options...
Goddy454 Posted November 19, 2023 Author Share Posted November 19, 2023 Our trucks here look for that, it was just an intermittent fault where I didn't notice the light was going off on the dash, I only caught it when the speed came down and I was not able to start it back up, that's when it showed itself. I have had this problem on others, but it was completely dead and threw a code. Thanks for your help. 1 Quote Link to comment Share on other sites More sharing options...
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