Yahoo Message Number: 1748 (http://groups.yahoo.com/neo/groups/Country-Coach-Owners/conversations/messages/1748)
Briefly, and hopefully, informative. If the diagnostics indicate that engine parameters are normal for fuel delivery, the next step to check for excessive soot would be air supply. If the engine receives the correct amount of fuel at the proper time, it would still be excessive fuel if the combustion air supply were inadequate. First check the air cleaner filter,{rarely the cause}. Next, check the charge air cooler for leaks. This cooler receives pressurization from the turbocharger, cools the exhaust temperature to condense the air, and delivers it to the engine. A very slight crack in the cooler assembly can seriously reduce the pressure in the air delivery system causing the problem you describe. Cummins Engine Company allowable drop in the cooler leak down test is 7psi in 15 seconds at 30psig.
For a clear picture of the test equipment and procedure, I refer you to the website www.duralite.net.
Another test which should not be overlooked is the operation of the waste gate in the turbo system/open, close properly.
Since our coaches are not equipped with a pyrometer to read exhaust temperatures, you should drive conservatively until the cuase is found. If either of the above defects are present the visible symptoms are soot and lack of power. Other events which occur are unburned fuel passing to the exhaust manifold where it ignites and could cause a cracked manifold. Internal engine temperatures rise much faster and higher than coolant temps will indicate causing accelerated engine wear or failure. If you have a boost guage or a Silver leaf, you should try to keep boost down to 12/14# and wait for another day to be first to the top of the hill.
Sorry for the length, contact me if necessary.
Dave 11430 02 Intrigue { with this problem }