As of 2015, common Cummins engine problems include steel dowel pins loosening and falling into timing gearcases of 5.9-liter 12-valve engines, and engine block cracking in its 1999 to 2002 5.9-liter 24-valve engines. Cummins built the 12-valve engines from 1988 to 1998 for Dodge Ram trucks. Dodge trucks with the problematic 24-valve engines have blocks with the number 53 cast on the front driver side of the engine. Misfiring is another common problem with Cummins 5.9-liter engines.
A steel dowel pin can vibrate loose after enduring years of movement and temperature changes. If the pin falls, it can damage the gearcase, cause an oil spill, or destroy the engine, depending on where it lands. To fix the problem, mechanics disassemble the front of the Cummins engine and cover the dowel pin with a tiny metal tab that holds the pin in place. They also tighten the gearcase bolts.
Cracked engine blocks allow coolant to leak out, and owners who do not fix the blocks need new engines eventually. Replacing 53 engine blocks with non-53 engine blocks corrects the problems permanently. Some owners fix their problems temporarily with stitch welding, block stitching and J-B Weld. These repairs may last 12 to 24 months, but cracks can form again in less time because the blocks' walls are weak.
When misfiring occurs, mechanics look for problems with the injectors and the cylinders by using the scan tool injector kill test function. The cylinder balance test results are not correct, because the test is not compatible with the Cummins 5.9-liter engine. An electrical problem is the cause of the misfiring if the injector wiring has less than 20 amps. Misfires can occur when an injector nozzle is stuck open or leaking, and fuel in the engine oil is a symptom.