01
Killer Dowel Pin (KDP) — 12-valve
A dislodged dowel pin drops into the timing case and can cause catastrophic damage on '89–'98 engines.
The fixInstall a KDP tab/repair kit to capture the pin permanently.
5.9L & 6.7L · 1989 – Present
Cummins: Top 10 Problems & Fixes
The inline-six Cummins is the torque king and incredibly tough, but each generation has signature issues — from the 12-valve killer dowel pin to the VP44 and modern emissions hardware. Sort them out and they run forever.
The 10 most common failures
What goes wrong on the Cummins — and how we fix it
Ranked from the problems we see most. Every one has a real, root-cause fix — not a band-aid.
02
VP44 injection pump failure ('98.5–'02)
Dead pedal, power loss, and stalling as the electronic VP44 pump fails — usually from fuel starvation.
The fixReplace the VP44 and add a quality lift pump to protect the new one.
03
Lift pump failure
Hard start and power loss; on VP44 trucks it starves and kills the injection pump.
The fixInstall a FASS/AirDog lift pump with a fuel-pressure gauge to monitor it.
04
'53' block casting cracks
External coolant seepage from a known casting flaw on certain '99–'01 24-valve blocks.
The fixMonitor and, if cracked, repair or replace the block.
05
6.7L EGR & DPF clogging
Frequent regens, derate, and turbo sooting on '07.5+ emissions trucks.
The fixClean/service the emissions system or delete with tuning (off-road).
06
6.7L VGT turbo sticking
Lost boost or over-boost as soot seizes the variable-geometry vanes.
The fixClean or rebuild the VGT turbo and service the actuator.
07
Injector failure / fuel in oil (6.7)
Misfire, smoke, and rising oil level from worn common-rail injectors.
The fixTest and replace failed injectors with quality units.
08
Front crank seal & KDP timing leaks
Oil leaks at the front cover, often discovered during a KDP repair.
The fixReseal the front cover and address the KDP at the same time.
09
Death wobble / track bar wear
Violent front-end shake after a bump from worn steering and track-bar components.
The fixReplace the track bar and steering joints; align the front end.
10
Automatic transmission failure
Slipping and limp mode as the 47RE/48RE/68RFE struggles behind big torque.
The fixBuild the transmission and valve body to hold the Cummins' torque.
Most-requested upgrades
Top 10 upgrades owners do to the Cummins
The modifications that add reliability and power. We install every one of these in the shop.
01
Lift pump (FASS / AirDog)
Steady fuel supply — essential to protect VP44 and common-rail systems.
02
Custom tuning
Unlocks the Cummins' huge torque potential safely.
03
Killer dowel pin fix
Cheap insurance against a catastrophic 12-valve failure.
04
CP3 conversion (6.7)
Adds fueling headroom and reliability on built common-rail trucks.
05
Built transmission / valve body
Holds the torque the engine makes without slipping.
06
Full gauge package
EGT, boost, and fuel pressure to run and tow safely.
07
4" exhaust & intake
Lowers EGTs and frees the factory breathing restrictions.
08
Injectors
Larger or fresh injectors for reliable fuel and added power.
09
Head studs
Holds the head down on tuned, higher-boost builds.
10
Upgraded turbo / EGR delete
More air and fewer emissions-related failures (off-road).
Got one of these on your Cummins?
Call the shop for a real diagnosis, or shop the O-Ringless parts and upgrades we install on our own builds.