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Ecker · 09-13-2006, 08:07 AM

On way to Discovery rally in Chama, NM from Alamosa one must cross two passes at over 10,000 ft. Three Discovery's with C7 and one with a Cummins ISB275 were running up to top of one pass. The Cummins with the lower HP was pulling an Excursion and thus much slower than C7's. The C7's decided to pull over into a viewing area to let Cummins catch up. When he came into sight, the C7's tried to move out but all three found they could not get engines to increase RPM. Drivers tried various things to get them moving and after a time did get going. However, they are very concerned. They live in this high mountain country and don't want to find themselves stranded in high altitude places. Anyone have any ideas on what could have caused this problem and what is solution.

Ecker · 09-13-2006, 08:07 AM

On way to Discovery rally in Chama, NM from Alamosa one must cross two passes at over 10,000 ft. Three Discovery's with C7 and one with a Cummins ISB275 were running up to top of one pass. The Cummins with the lower HP was pulling an Excursion and thus much slower than C7's. The C7's decided to pull over into a viewing area to let Cummins catch up. When he came into sight, the C7's tried to move out but all three found they could not get engines to increase RPM. Drivers tried various things to get them moving and after a time did get going. However, they are very concerned. They live in this high mountain country and don't want to find themselves stranded in high altitude places. Anyone have any ideas on what could have caused this problem and what is solution.

GStream40 · 09-13-2006, 09:13 AM

It sounds like what they were experiencing was the power loss of being at the 10,000+ elevation without the boost of the turbo because at idle and until the rpm's are high enough for the turbo to create the needed boost pressure it is the same as a naturally aspirated engine.

A naturally aspirated engine loses 3% of it's power for every 1,000 ft. of elevation. So at 10,000 ft. they lost 30% of their power at idle and low rpm with no boost pressure.

A turbo charged engine with the turbo boost pressure built up loses 3% of it's power for every 10,000 ft of elevation, BIG difference.

Probably after they were able to get the coach moving and the boost pressure built, they were okay because the turbo was pushing more air/oxygen into the engine for more power.

When you are used to an engine putting out a set level of power at a lower altitude and all of sudden you have 30% less to get your load moving, it will seem that you have a big problem with the engine, but not really, just thin air/oxygen without the turbo boost at lower RPM's.

I hope I explained it correctly so it can be understood.

Ron

wallynm · 09-13-2006, 10:53 AM

In addition to Ron's explanition which I agree with the engine is programmed to start derating based on how much power it is able to provide to protect other componets. In most cases you need to run in a lower gear say 5 to provide for proper cooling. RTFM (Read the Factory Manual) for high altitude oeration.

Ecker · 09-15-2006, 05:16 AM

I wasn't happy with the info I had so I went back and checked with the owners. The three C-7 owners did not all expereince the problem at this time. One had the problem on this climb the others earlier. One was on Berthoud Pass waiting in constuction line and when given ok to go he could not get engine to increase RPM i.e no response to accelerator. He had to wait for next cycle and then tried again and that time it moved. I'm not sure of details of second. For the third person, he shut off his engine(trying to save fuel while waiting) and when he went to restart it wouldn't. He tried several times and it did finally start but he had no action form accelerator pedal similar to the Berthoud Pass incident and also he was finally able to get it to respond. I checked the physical area yesterday and it is a level viewing area on the climb so there was no angle to coach while engine was off.

wallynm · 09-15-2006, 05:27 AM

I guess I would start checking fuel filters. Some Freightliner unit came from the factory with only one filter/water separator. Cat recommends two filters - you can check out the catrv club url referenced in my signature for more info.

Would also check the air filter and turbo fittings to make sure I was not plugged and/or losing boost.

Last but least I would discuss with a Cat Shop. Your nearest best bet from Chama is Waggner in Albuquerque. I have used them and am happy with their response.

GStream40 · 09-15-2006, 06:15 AM

ecker,
That is different from what your first post was. I would say that they need to contact CAT RV helpline and see what they say about the problems themselves and describe in detail to them.

Ron

Kiwi · 09-15-2006, 10:36 AM

I had my coach with C7 up on Trail Ridge Road in RMNP. I think that is around 12,000 feet. I was towing a Honda Pilot (4500#). I had no problems while driving, or after parking. The coach and engine performed superbly.
Walt