Can't climb hills - Downshifting is only sporadically increasing RPMs.

[Stan Simpson]

Prior to our trip West to the Black Hills and Yellowstone, I had the coach serviced. New air cleaner, all new filters, lubed chassis, checked fluid levels, belts, and hoses. No issues.

Got in to South Dakota on I-90 where there lots of long uphill climbs, many a mile or more. With cruise on at 64 mph, as soon as we started a climb, and the speed would drop to 61-62 mph, the transmission downshifted, and the RPMS went to 2000, which was expected. However, the increase in RPMs only lasted a few seconds, and we gradually lost speed, down to as much as 46 mph by the time we reached the top of the grade. I took the cruise off, and manually shifted to 4th gear when we started a grade. Again, the RPMs went up to 2000 but only lasted a few seconds and then speed and RPMs dropped. The same thing with the other low gears.

When we got to the Black Hills, and its steep climbs in places, at some times we were down to 17mph. We are leaving Monday, have an appointment with Allison in Sioux Falls for next Thursday (we have cancelled Yellowstone), and are heading home.

Has anyone else had this experience, and if so, what was the diagnosis, and remedy? Will I do any further damage, if there is any, driving the 400 miles to Sioux Falls? The same certified Allison service center has a branch where I live. Can I go all the way home?

TIA

[David T. Richelderfer]

Air in the fuel line?  -  http://beaveramb.org/forum/index.php/topic,834.msg4955.html#msg4955

Partially restricted fuel filter?  -  http://beaveramb.org/forum/index.php/topic,8357.msg57655.html#msg57655

[Joel Ashley]

Look at the bowl under the fuel filter, Stan, and see if there’s black debris floating around.  You may have got into some bad diesel somewhere, or had some algae grow that didn’t get concentrated enough and sucked up until the fuel level dropped during the trip, and now is constricting fuel flow in the filter.  Another new filter (or two?) may be helpful, depending on the degree of contamination.

Occluded filters are probably the most common cause of your symptoms.  Our farmer nephew in Idaho was taking me on a “demo” trip 25 years ago hauling beets to the receiving station in one of his many trucks, and had to stop mid-trip to put on a new filter;  my first exposure to such a malady.  He carried spares enough that he probably kept his parts supplier in business.

Joel

[Dale Soule]

I had a similar problem going to Cody last year.  Driving with cruse on towing into a head wind.  Engine started to heat a little, then "D" rate , let it cool down, took cruise off, drove slow 45 mph for about 3/4 miles .  cruise , hills, and heat are not friendly.

[Fred Brooks]

   Stan'
 I have always considered hill climbing as a fun part of the journey. It requires participation and management skills from the driver. Most coaches do not like hill climbing with cruise control on. When the coach loses 5 mph, it drops the cruise control out. Coaches have issues hill climbing in 6th gear (double overdrive) and even 5th gear (single overdrive) if you have a toad. My coach has a "sweet spot" of 1800 rpm. It becomes my objective to be at 1800 rpm for any substantial hill in a gear that won't lose road speed, usually 4th and sometimes 3rd. This ensures the following: 1- not lugging the engine which causes excessive engine heat, 2- radiator fan speed is optimal for cooling, 3- not getting stuck behind an 18-wheeler in the right lane. I am not sure what is causing the intermittent issue. Sounds like air in the fuel or a fuel check valve. Dave may have some ideas. Fred