Cummins engines show up in nearly every class of truck we work on: Ram pickups and chassis cabs, the Nissan Titan XD, medium duty trucks, buses, diesel pushers and Class 8 tractors. RDI Power repairs and services all of them at our Brooksville shop and on-site, from a water pump on a 12-valve to an overhaul on a heavy truck engine. Whatever the engine, the work starts with a diagnosis that proves the cause.
Ram 5.9L and 6.7L Cummins
The B-series Cummins in Ram trucks has gone through several distinct designs, and each has its own pattern of problems. Ram trucks are diagnosed with WiTECH, Stellantis’ factory software; see our Ram and Dodge diesel repair page for the rest of the truck.
5.9L 12-valve (1989 to 1998)
Mechanical injection, first with a Bosch VE rotary pump and from 1994 with the Bosch P7100 inline pump. These engines are simple and durable. The known risk on 12-valve and early 24-valve engines is the dowel pin in the timing gear housing, often called the killer dowel pin, which can work loose and fall into the gear train. Securing it is cheap insurance against expensive damage.
5.9L 24-valve (1998.5 to 2002)
These trucks use the Bosch VP44 electronic injection pump, which depends on fuel flow from the lift pump for cooling and lubrication. A weak lift pump shortens VP44 life, so supply pressure gets tested any time this pump is in question. Some blocks from this period, identified by a 53 casting number, are known to crack along the side of the block.
5.9L common rail (2003 to 2007)
High-pressure common rail with a Bosch CP3 pump. Clean fuel and fuel filters on schedule matter more here, because injector wear shows up as hard starts, smoke, rough running and excessive fuel return.
6.7L (2007.5 on)
The 6.7L added a variable geometry turbo, EGR and a DPF, and later trucks added SCR with DEF. The repairs we see most are a VGT that sticks from soot, EGR valve and cooler problems, DPF regen trouble, NOx sensor failures and DEF system faults. Many of those trace back to how the truck is driven, and short trips and long idles are hard on all of them. More on our DPF, EGR and emissions repair page.
Nissan Titan XD 5.0L Cummins V8
Nissan offered a Cummins-built 5.0L V8 in the Titan XD from 2016 to 2019. It is far less common than the Ram engines, and it gets the same diagnostic approach: scan data, fuel system testing and a look at the emissions system before parts are ordered. See our Nissan Titan XD service page.
Medium duty: ISB, B6.7, ISC, ISL and L9
Many medium duty trucks, buses and diesel motorhomes run Cummins power: the ISB and B6.7 in Freightliner, International and Mack medium duty trucks, and the 8.3L ISC and 8.9L ISL and L9 in larger Class 6 and 7 trucks, buses and pushers. Common work includes fuel system repairs, turbochargers, aftertreatment faults and cooling system problems. A failing EGR cooler is a frequent cause of coolant loss and overheating on these engines; our article on faulty EGR coolers on the Cummins ISB covers the warning signs. We also repair the rest of these trucks, from brakes and suspension to transmissions and electrical systems, and our RV chassis repair page covers Cummins-powered motorhomes.
Heavy duty: ISX15, X15, ISM and older engines
On Class 8 tractors we work on the ISX15 and X15, the 10.8L ISM and older engines such as the 855. Common ISX and X15 repairs include EGR valve and cooler failures, variable geometry turbo actuator problems, fuel system faults and DPF, SCR and DEF doser problems. On older engines like the 855, an in-frame overhaul with new liners can put a proven engine back to work for a long time. Heavy truck repairs beyond the engine are covered on our semi and heavy duty truck repair page.
Maintenance that keeps a Cummins healthy
Basic engine maintenance on any Cummins means oil and filter changes, fuel filter replacement, air filter service and coolant maintenance on schedule. The truck around the engine has its own list: transmission, differential and transfer case fluids, power steering service and brake fluid. A maintained B-series routinely runs for hundreds of thousands of miles, and skipped fuel filters and neglected coolant are 2 of the fastest ways to shorten that.
Parts and performance
We choose parts based on how they hold up in service. Sometimes the original equipment part is the right call. Sometimes an updated aftermarket design solves a known weakness better than the factory part did, and we will tell you which and why. Performance upgrades follow EPA rules, and they only pay off when the parts are matched to the truck and installed and tuned correctly; see diesel engine tuning.
Every Cummins repair comes with a digital vehicle inspection with photos and technician notes, and our 3-year/36,000-mile labor warranty. If your Cummins is down or running wrong, request service online or call the shop, and tell us what it is doing.