Details: The truck drove in with the malfunction
indicator light on. The first thing the tech did was to check for
spark and injection timing. Both were correct. On recommendation
of the Tech-Asist Consultant, the tech connected a scope and
pressure transducer to number one cylinder to check compression.
In scope pattern, he noticed that the exhaust stroke pressure was
rising significantly as if the exhaust valve was barely opening.
After removing the bank one valve cover and cranking the engine
over with the ignition disabled, the tech noticed that the number
one cylinder exhaust rocker was hardly moving. Upon further
inspection, he found that the lifter was completely broken (See
good and bad pattern images).
Good – Flat exhaust pattern
Bad – High exhaust spikes
Confirmed Repair: The tech replaced the lifter
and the engine ran perfectly after the repair.