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Gearhead383 · 06-11-2013, 05:48 AM

We are driving down the highway at 65 and an hour before we get to our destination, my cruise control downshifts from 6th to 5th gear. I was not pulling any kind of grade, just flat, open road. I gave it a sec and canceled the cruise and the transmission shifted into 6th. I resumed the cruise and it was fine for about a minute then it downshifted back into 5th. I canceled the cruise all together and waited a few minutes. When we were on a nice flat road and the engine was producing very little boost, I enabled the cruise. Within 30 seconds, it downshifted again. This time I pressed the up arrow on the shift pad and the trans would not upshift. I canceled the cruise once again and placed the trans into economy mode, applied the cruise and had the same result; downshifted within 30 seconds. Once we arrived for the weekend, I decided to surf the net for some answers and was not very fruitful in my search. We headed home after a few days so I decided to give the cruise another try. Still had the same results. So I made the 8 hr trip without cruise, this sucks!
When I got home, I called Monaco tech support and the guy on the other end told me he had never heard of that before and to call Cummins. I phoned the local Cummins shop and they directed me to a shop that does Allison transmissions (3000MH). I spoke with the lead Allison tech and he was puzzled too. The fluid level is correct and there are no codes stored in the transmission. I think some of these techs are missing the point that everything seems to be working normal except when the cruise is engaged. I asked each person which device is responsible for controlling the cruise... is it Cummins, Allison, a combination of both or does it have its own controller. No one I spoke with had an answer. I would think there has to be some sort of problem with a TPS or speed sensor somewhere that only effects the cruise. Any suggestions?

Thanks.

Tom-NC · 06-11-2013, 06:05 AM

Hi,

I don't know if this helps but years ago I had a cruise problem that it would disengage every time I stepped on the accelerator. When we stopped at a rest area to take a break I opened the hood to check things out and my wife found a vacuum hose disconnected. I reconnected it and no problem. Maybe there is a vacuum leak if the cruise works on vacuum. This is only a guess.

Dutch Star Don · 06-11-2013, 11:47 AM

Ron...Do you have a SmartWheel?

When the cruise control is set and you're waiting for it to downshift (malfunction) is the coach slowing down prior to this happening, or does it maintain the same speed you set the cruise at.

Pusherpilot · 06-11-2013, 12:01 PM

Did you try it at a higher speed?
What Don said plus, was it trying to accelerate? What I'm getting at is that the Cruise control has the ability to speed up without disengaging. If that function is malfunctioning that could be it.
Ron

Skip426 · 06-11-2013, 12:16 PM

Just as a point of clarification.

The cruise control worked fine for the first 7 hrs. of your away trip before it started acting up ?
Was any portion of the trip , driving on wet roads , raining condition ?
My understanding ; of cruise on my coach; The Engine Control Module controls the throttle (rpm ) and on shared info the Trans Control Module controls the gear. The cruise type ( hard to maintain exact speed or soft to allow 3 to5 mph. drop before down shift) is a TCM program.
Next question, do you have the new style shift control with the current gear and selected gear display ?

Skip426 · 06-11-2013, 03:27 PM

Ok , a mind is a horrible thing to loose

I've seen a similar problem on Dodge Cummins ,and forgotten about it for a while, and I'm going to go out on a limb and say this problem started about an hour after a fuel stop.
You need to check your fuel and air filters .
And here's the reason, a partially plugged fuel or air filter will result in a slight loss of power, meaning you have to use more throttle to maintain speed. The Throttle Position Sensor reading is higher, without cruise on the TPS reading is not high enough to call for a downshift; BUT ; in cruise the program sees the TPS reading as a demand for more power than can be produced at the engine's RPM in 6th gear, so the program shifts the trans down to 5th, thinking it needs to be in 5th to maintain the set speed on the grade that would require that TPS reading for the given engine RPM.
So the possibilities are very poor fuel quality, pugged fuel filters, plugged air filters or a combination of all 3.

Mike Canter · 06-11-2013, 04:36 PM

I like what Skip suggested. If you haven't replaced your fuel filters in the last 10k miles or close to it then maybe time. Check your air filter indicator. Also just for interest there is no vacuum on a turbo charged diesel. The other thing to check is the trouble codes on the Allison transmission by turning on the ignition so the pad is on a push the UP and DOWN arrow keys at the same twice. Check your Allison manual on doing it or I can post the instructions if needed.

Gearhead383 · 06-12-2013, 05:45 AM

Thanks for all the replys. Let me try and answer what I can.

Tom-NC- As Mike stated, there would be no vacuum hoses on my diesel, this unit is completely controlled by computers.

Don- No smart wheel here. It does maintain whatever mph I have it set to. Even going down a slight grade it won't up shift.

Ron- I will try that next. I was wanting to get out on the road and set the cruise at 65 then continue to hit the "resume" button to see if it would accellerate up to 70-75 and see if it would up shift.

Skip- Yes it did. We drove for 4.5hrs then stopped for the night. Fueled up in the morning and continued for 2.5 hrs before it started to act up. It was a nice day and the roads were smooth and dry. I assume my shift controller is the selected gear type. When I put it in "D", it displays 6 all the time unless I hit the down arrow, then it will display 5.
Another good point Skip. When I called Monaco about this, they stated fuel filters as well. As mentioned earlier, I did get fuel that morning and both my fuel filters were changed late last summer... maybe less than 1500 miles on them. I didn't feel any decrease in power while driving without the cruise but your explaination does make sense. But I would have thought the trans would have shifted into 6th driving down a slight grade when the boot was under 10psi.

Mike- I changed the air filter this spring and have only made 2 trips totaling under 500 miles. I did check the codes in the trans and there are none. An Allison tech wanted me to put the trans in economy mode and take it for a drive and see if anything changes. That is another test I will perform when I take it out hopefully tonight.

If the motor was down on power, I would think that I might feel it because I do pull a 28' enclosed trailer. Very seldom do I take the MH out by itself. I bet 90% of the time we are using it to get from one race track to another. So I'm wondering if Skip's theory is correct and the cruise might function normally because I'm not pulling the extra weight. That maybe I did get some bad fuel. I did refuel about 2.5 hrs from home so maybe changing out the filters might be what is needed here. Thanks for all the inputs and advice. I will continue to report my findings until this problem is resolved.

Skip426 · 06-12-2013, 11:59 AM

These engines ( fuel systems ) run any un-used fuel back to the tank, at Dodge Cummins training they said only 30% of the fuel supplied to the engine is used by the injectors ; even at full throttle; the rest is returned to the tank. So in 2.5hrs run time all the fuel in the tank could have been through the filters twice. They can plug up fast. It would be interesting to see the filters cut open, if that cures your problem.

Gearhead383 · 06-12-2013, 12:34 PM

Skip- That's a great idea. It just so happens that I have a tool that can do that. I'll let you know. Just need to look to see if I have any extra filters at the house.

YC1 · 06-12-2013, 12:44 PM

Ditto the fuel filters.

Dupdyke · 06-12-2013, 07:04 PM

If yours is like my isl 400 dynasty you should have two filters and the first one usually has a separator bowl on the bottom and you might just see grey or brown goop in it. If you have normal power you might look at contact cleaner on the engage disengage and the jake brake switches. You sure you dont have some form of smart wheel Most have those buttons on the wheel so its semi smart.

Hope to not have your problem as I leave in the morning for gillette to work the rally and I hate to run without cruise...

Gearhead383 · 06-13-2013, 05:21 AM

That's exactly what I have Dupdyke. I looked at the bowl with a flashlight and I couldn't see any sediment. I looked on my shelf and I only had the fuel filter that mounts onto the engine so I ordered a couple more that uses the separator bowl. Winds were blowing pretty strong last night so I didn't get my test drive in. The filters might be here tomorrow and I can change them out and test drive this weekend. I'll post updates. Thanks all!

Gearhead383 · 06-20-2013, 11:57 AM

***update***
I received my fuel filters Wed afternoon and changed them both. I hooked up to my trailer and began our 4 hr journey. I am happy to report that the cruise controls works again!

When I get back home, I will cut the filters open and see if there is any visible evidence as to the restriction.
I would like to thank everyone for there suggestions and help with this issue especially Skip for hitting the nail on the head.

You guys are great!