Thanks for the reply , and your patience.
To start , there are a number of conditions that can cause excessive black smoke from the exhaust .
· Turbo Boost pressure too low , or a defective boost pressure sensor.
· Air intake , or exhaust leaks – resulting in low boost pressure
· Fuel drain line restriction
· Malfunctioning injector or multiple injectors.
· Improper Injection pump timing
Most or all of the above problems would likely be acting up “all the time”. I don’t think your problem is any of these listed above.
Your engine has a Bosch VP44 injection pump. I believe there is an intermittent issue with the injection pump. The VP44 may have electronic issues , or mechanical issues or both.
While looking up the recall history for your engine , I noted that there are several open Cummins warranty Campaigns , and an open TRP (temporary repair practice) for your engine.
Two of the campaigns involve the possible replacement of the fuel lift pump , and recalibrating the ECM software.
My recommendation is that you first have these recalls and updates performed by a qualified Cummins service center. A malfunctioning lift pump can affect the operation of the VP44 , set fault codes , and cause driveability problems. I suspect that your problems will be related to the VP44 injection pump...After the recalls and updates have been performed , then see if there is still a problem , and troubleshoot from there. The lift pump , and software updates should be done first.
Here is some more information on the service campaigns.
Cummins Inc. is conducting a recall of ISB engines, model year 1998 to model year 2002 (which includes engines manufactured between 1996 to 2003), installed in school buses, transit buses, and emergency vehicles in the U.S. and Canada due to a possible problem with the fuel lift pump. Cummins Inc. has determined that a small percentage of these engines may experience a stall condition.
This safety Campaign authorizes service repair locations to install a replacement fuel lift pump on engines in the eligible population. The replacement pump is an improved design that eliminates this potential stall condition. To provide further protection, a pressure switch will be installed, coupled with the existing check engine light, to warn a driver of low fuel inlet pressure conditions.
This TRP authorizes repair shops to replace the fuel lift pump and recalibrate the ECM on engines that experience Fault Code 779 after the completion of Campaign 0504 repair. It covers eligible engines up to 10 years from their date-in-service.
There is also an open alternator bracket campaign for your bus.
This Campaign is to address a design issue with the alternator support brace on ISB 5.9L engines used in Freightliner and Blue Bird chassis, in school bus applications. The support brace, part number(NNN) NNN-NNNN when used with the upper alternator support bracket, part number(NNN) NNN-NNNN may break or its mounting hardware may loosen causing the alternator to fall. This Campaign will authorize replacement of the lower alternator support brace and installation of an updated support bracket.
Please let me know if you still have any questions or concerns.