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Old 07-11-2015, 08:20 PM   #1
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DP seems to cut out under loads

Hi all, first post here. We just got a new to us 2013 Thor Tuscany XTE 40EX with the ISB 6.7 360hp. We were on the first outing in the new coach and on the I-10 going through the pass around Palm Springs, where the windmills are, we seemed to be experiencing a severe loss of engine power going up the grade. The rpms would be 2000-2500 and all of a sudden the trans would buck and the rpms would drop down to 1000-1200 or so. There didn't seem to be any throttle response until a few moments later when I could once again depress the accelerator and try to resume some speed. This happens continuously.

The turbo boost was 30 when this happens. I can also get it to happen on flat ground like on a freeway onramp. Once the engine reaches a certain rpm there is no throttle response.

The moho is currently at Freightliner, and they have said they couldn't find anything wrong with the engine operation and it could be a problem with the Allison.

I'm a 30yr GM technician and work on diesel engines daily so I am aware of their behaviors. Could I be expecting too much of the 360? I do find this to be disturbing if it is normal. It is difficult to get on the freeway when you cannot accelerate.

Should there be chugging and jerking sensations when climbing grades?

Looking forward to all of you seasoned DP owners input on this.

Keith
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Old 07-11-2015, 08:45 PM   #2
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No there shouldn't be jerking and chugging. Have you changed the fuel filters? That is generally the first place to start with lack of power and diesel. But I do suspect perhaps there is an electrical connection issue. But the filter is certainly where I would start.
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Old 07-12-2015, 06:11 AM   #3
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any lites on when this occurs. Sounds like computer maybe is derating motor?
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Old 07-12-2015, 07:21 AM   #4
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Quote:
Originally Posted by Bucky1320 View Post
No there shouldn't be jerking and chugging. Have you changed the fuel filters? That is generally the first place to start with lack of power and diesel. But I do suspect perhaps there is an electrical connection issue. But the filter is certainly where I would start.

Sounds like classic dirty fuel filters symptoms. Bucky is spot on.


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Old 07-12-2015, 08:33 AM   #5
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Also sounds a bit like tranny is up shifting more then a gear at a time ... we learning to drive our coach, I found that too little TPS (throttle pressure) would allow pre-mature shifting and sometimes skipping a gear .... something I had to get used to ...
or maybe a slight adjustment is necessary .......... #justathought
and ...
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Old 07-12-2015, 08:36 AM   #6
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Change your fuel filter.

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Old 07-12-2015, 08:36 AM   #7
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bucking

Had almost the exact same problem last year. On mine it was the auto traction control kicking in. Apparently if you lose speed when accelerating the computer assumes tire slippage. After talking to a HR tech I changed the fuel filters an no more problem. Also check your manual, I believe 2500 RPM's is red line for that engine. It's at least darn close to red line.
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Old 07-12-2015, 09:16 AM   #8
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I agree with the filters needing replacement. The 30 PSI boost pressure (low if full throttle and pulling a hill) tells me fuel restriction, (fuel filter clogged)../..

Low engine power will fool your transmission into doing strange things...
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Old 07-12-2015, 09:20 AM   #9
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Was your retarder switch on , cruise control on position?
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Old 07-12-2015, 09:23 AM   #10
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With the retarder on, attempting to accelarate mid down shift by the retarder will cause a lag and stall accelaration on mine!
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Old 07-12-2015, 09:51 AM   #11
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An ISB is a little small for a 40 ft coach but that's what you got. The power band on that engine is in the 2200 to 2500 RPM range and so you need to use your transmission pad to select the proper gear to hold it in that power band. I believe what is currently happening is that you are letting the transmission do the shifting and once you reach the maximum RPM, it is upshifting to protect the engine from overspeeding. Of course your RPMs drop and your boost drops because you are at wide open throttle(WOT) and low RPMs.

So next time over the pass try this. Move over to the right lanes and as you start to slow, push the down arrow on the transmission pad. You should get a downshift and an increase in RPMs. As you continue to climb, do not go to WOT at anytime, but use your gear selector to keep your engine in that power band mentioned above. Depending on what the road does when you are over the top, either stay in that gear or go back to drive. If you have an exhaust brake, it should be on.
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Old 07-12-2015, 01:01 PM   #12
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Ok, thanks for the replies.

I am totally new to DPs so it will take some time getting used to them. It is difficult not being able to hear what the engine is doing.

I am aware that there are higher output engines available in some coaches, but those are usually only installed in the high dollar rigs, not that ours was cheap or anything, but those with the big dog engines are definitely out of our reach for now. We got a pretty good deal on ours with relatively low miles at an RV show and it is a 2013 which sweetened the deal for us.

As I said the rig is currently at Freightliner, and the tech who drove it Friday said he didn't see anything wrong with the engine operation and felt it may be a trans problem. I personally don't think there is anything wrong with the trans. I may just go and pick it up Monday morning and try some things on our next trip. Sounds like I have some options to consider when the power goes away leaving it in drive. We had a brief road test with the delivery person when we bought it but he was not a DP owner so he probably didn't know any more about them than we did.


The fuel filters were supposedly changed before we took possession of it, but I hear there are 2 filters so maybe they only changed the one in the separator? I'll look into that when I get it home.

Thanks for the responses, it is appreciated.

Keith
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Old 07-12-2015, 04:35 PM   #13
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There are 2 fuel filters on the 6.7. like you said dealer probably only changed one. Sounds like fuel to me also. Mine does not buck during a climb or hard acceleration.
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Old 07-12-2015, 07:13 PM   #14
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I just had symptoms similar to what you are describing but the amber warning light also came on. It turned out to be some sort of engine speed sensor that was bad. Tachometer was not affected but the sensor fed information to the computer. Had to go to a Cummins repair shop to retrieve codes. Good luck with your solution.
------ Jim
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