ISL 400 losing power on grade uphill

[Bosskat]

In a 2005 Endeavor while driving at 55 or so MPH and come to a hill the drive train does not seem to downshift to keep me at a reasonable speed.

2005 HR Endeavor - 400 HP Cunnings engine - Allison World transmission.

Driving on level at 55 MPH and start up a grade. Seens to downshift but then up shifts. Speed drops to 25-35 MPH. down shifting manually to 4 then 3 does not seem to help maintain my speed. What could be the problem?

[Perry White]

Is it when you are using speed control or when you are manually pushing on accelerator?

[The Danes Are Coming]

Hi Bosskat



For any information on your RV you have come to the right place.

I have an ISL 400 and I have the option to shift manually should I so desire. Never had a problem down shifting automatically but what about manually? Does this work?

[Perry White]

If it's when you are on speed control ,your droop speeds might be set too high. They let the coach float 1 or 2 MPH before applying or releasing power. I've seen some set as high as 6 or 7 MPH above or below. You can reset them with Cummins Insite.

[radams]

Do you have the transmission in Econ mode? If so, that has the effect of limiting downshifts for the purpose of improving MPG.

[Bosskat]

Quote:

Originally Posted by Perry White Is it when you are using speed control or when you are manually pushing on accelerator?

It is when manually pressing on the accelerator. As I was driving on some hilly roads, I had pressed the down arrow to stay in 5th gear. Would this stop the transmission from down shifting? If so I could downshift manually to 4 or 3?

[Bosskat]

I have not yet used Econ Mode, as I was not sure what I does for me.

[Iron Man]

How is your pickup from a standing start? Can you tell what you turbo output is when going up the hill? What are you pulling for a toad? Have you check air/ful filer?

[Bosskat]

How is your pickup from a standing start?
Pickup from a standing start seems ok, but I dont accerate hard.

Can you tell what you turbo output is when going up the hill?
I don't know how to do this.

What are you pulling for a toad?
My toad is a 2001 Satern.

Have you check air/ful filer?
All filters were changed with the oil change less than 200 miles ago.

[Iron Man]

Was this happening before the filter and oil change

[Bosskat]

Yes it was a problem prior to the filter and oil change. I was hoping that would help, but it didn't.

[LindyT]

If you've changed the fuel filters and checked the air filter, I would check boost pressure (there should be a "turbo" "turbo psi" or "boost" gauge on your dash) - you should be 25+ at maximum load. It's possible you could have a loose CAC clamp or similar if that's indeed the issue.

That aside, did you just recently obtain the coach? Was performance on grades ever up to your standard? I'm not sure if you just purchased this coach or if this is your first DP, so I apologize if I appear to be insulting your intelligence, but large diesels behave differently than gassers. If you lose your momentum (ie: you let off the accelerator at any point) on a hill, you will not get it back - downshift or not.

If you are concerned about loss of power, you may visit just about any Cummins authorized distributor and they can put the coach on the dynamometer to see if there's an obvious issue.

Good luck.

[Bosskat]

If you've changed the fuel filters and checked the air filter, I would check boost pressure (there should be a "turbo" "turbo psi" or "boost" gauge on your dash) - you should be 25+ at maximum load. It's possible you could have a loose CAC clamp or similar if that's indeed the issue.

Thank's I don't know, but will check as soon as I go out next. The "boost gauge" is placed where I don't see it unless I lean around the steering wheel. I will do that.

That aside, did you just recently obtain the coach? Was performance on grades ever up to your standard? I'm not sure if you just purchased this coach or if this is your first DP, so I apologize if I appear to be insulting your intelligence, but large diesels behave differently than gassers. If you lose your momentum (ie: you let off the accelerator at any point) on a hill, you will not get it back - downshift or not.

We purchased the coach in late 2009 and it is our first coach so, I appreciate all your comments. As a novice driver I thought performance was fine on our first trip to Florida in spring 2010. I think it has just gotten worce over time. I find your answer very interesting as I didn't know anything about these vehicles except that they looked great. We did have a 5th wheel and Ford F350 (Diesel) and I never noticed anything like this loss of power with it.

If you are concerned about loss of power, you may visit just about any Cummins authorized distributor and they can put the coach on the dynamometer to see if there's an obvious issue.

After I check out the turbo boost, I will visit Cummins if I find low pressure.

Thanks for your comments

[Bosskat]

Is turbo boost preasure something I can adjust?