Cruise Control Revisited?

[9speed]

Hey,I was reading a post from a couple days ago about the cruise control. I have a strange problem, and looking for a place to start. I have a fleet of most CH613s, but some newer CXNs and CHUs, all 9-speeds, all w/cruise. These trucks mainly pull pneumatic bulk trailers (hauling flour)and to off-load, they engage the PTO to run the blower, then bump the cruise to bring the RPMs up to bring up the tank/line pressure (under ideal conditions it takes about an hour and a half to unload 51,000 lbs of flour). The problem is one of these trucks ('02 CH613) has started intermittantly kicking the cruise off while unloading, causing the tubes and hoses to clog with flour. Needless to say the driver ain't too happy. He says that the cruise works fine going down the road (set at 63 mph, it will stay there all day). PTO engagement shouldn't affect this should it, as you can set the cruise to bring up RPMs while sitting still in the lot (over-riding the auto-shut-down)so you can run the heat or A/C, without the PTO engaged. I hate to just "throw parts at it" but this has me buffaloed? Anybody else ever ran into this problem? Thanks

[counterman6]

Could it be the cruise control relay over heating? That may be an easy place to start.

[ThaddeusW]

Could it be the cruise control relay over heating? That may be an easy place to start.

Good point but his driver did in fact say it works fine down the road. BUT does time play in as a factor here?

how long does the blower run before the cruise kick out? I would check that relay first like counterman6 said and also time how long it takes to kick out. Park the truck and run the blower as if you were unloading and have a stop watch handy. see if it kicks out at a regular interval. If the kick out time is pretty consistent then you have something tripping out possibly from overheating. If its intermittent then I would suspect a bad connection or other electrical problem

[rhasler]

A 2002 CH613 will have VMAC III controls. There is no cruise control relay. Cruise control is instead controlled by the VECU. By default the cruise control will drop out if the accelerator, clutch, or brake pedal are pressed while the cruise control/electronic hand throttle is active. In addition to these "drop out" conditions it is possible to have "customer defined statements" programmed to drop out the cruise/EHT. With custom body installations, such as mixers of trash trucks, there are often custom drop outs programmed. I would start out by checking the clutch switch. The engine brake also operates off of the clutch switch input to the VECU, so if you also get some comlaints about the engine brakes operation that would be a good place to start looking.

[9speed]

Thanks rhasler,

I had already checked the clutch switch, but nothing on the brake or accelerator. The clutch switch checked good, but with this problem being intermittant/inconsistant....? I wondered, because Mack, unlike everyone else, you can depress the clutch and it will take out the cruise, but it immediately "re-engages" as the clutch pedal returns. When the truck is stationary, this is not so! Opening the clutch switch deactivates the cruise until it is manually reset. I thought that maybe going down the road, if the clutch switch momentarily opened, the driver may not notice, as it came back instantly. If a similar vibration kicked it out while sitting still (unloading) it wouldn't. I'm going to look at brake and accelerator inputs now. Would something like a (false) overheat condition affect this? The same truck has been written up for that before. Thanks for the help guys

[rhasler]

Thanks rhasler,

I had already checked the clutch switch, but nothing on the brake or accelerator. The clutch switch checked good, but with this problem being intermittant/inconsistant....? I wondered, because Mack, unlike everyone else, you can depress the clutch and it will take out the cruise, but it immediately "re-engages" as the clutch pedal returns. When the truck is stationary, this is not so! Opening the clutch switch deactivates the cruise until it is manually reset. I thought that maybe going down the road, if the clutch switch momentarily opened, the driver may not notice, as it came back instantly. If a similar vibration kicked it out while sitting still (unloading) it wouldn't. I'm going to look at brake and accelerator inputs now. Would something like a (false) overheat condition affect this? The same truck has been written up for that before. Thanks for the help guys

You should also be able to set up "temporary drop outs" to make the EHT reengage after the clutch switch returns to the closed position. As for an overheat situation causing the problem, I wouldn't think so, but I've seen bad diodes in mixer body applications (in the hydraulic cooling fan circuit) keep the engine running when a breeze was blowing the fan enough to make it turn.

[pooch]

Your cruise control should be set as an all speed. I suspect it is min max right now. This can be done by your dealer, tell him your synthoms and your rpm parameters. There is various PTO variations in the programing. You may require a bit of wiring to let the computer know it is in PTO mode.