EGR Marbles

Have you ever serviced an EGR valve on a 6.0l Power Stroke diesel engine only to have the truck return with a repeat EGR concern? A minimum stop performance code P1335 indicates that the EGR valve is not fully closing which would be surprising if the valve is new. The open valve will cause performance concerns like a lack of power, hesitation smoke and stalling. The engine may not even run if the EGR valve is open enough when it should be closed. Remove the EGR valve and inspect it for contamination like pea-sized carbon chunks we refer to as EGR Marbles. Typically EGR valves stick when they are gummed up or clogged with the soft greasy carbon that collects around the mixer area of the intake manifold. EGR Marbles are quite different in that they are dry and quite hard. They form on the cooler side of the EGR valve inside the outlet side of the EGR cooler and in the port that leads from the cooler to the EGR valve inside of the intake manifold. Often EGR flow is restricted or even completely blocked by this formation but sometimes the carbon breaks apart allowing pieces to bounce around eventually becoming small rounded chunks that are small enough to get caught in the EGR valve when opened. When broken apart the EGR Marbles reveal a gray colored composition, sometimes layered with black carbon. The gray material is evidence that the EGR cooler is leaking coolant which attracts carbon before it burns off leaving the lighter residue. It is possible for an EGR cooler to leak only when very hot which means it may pass the normal test procedures. Once diagnosed the cooler will need to be replaced and the intake manifold will need to be cleaned or replaced if blocked solid or deemed not cleanable.