A certified Bosch dealer should be a good source. I've never replaced just one injector so I don't know how you should proceed. I suggest you make sure a replacement injector is a close match for the other five. I don't know if you'll have to exchange all six and buy a matched set or . . . . . ? I would certainly ask the injector shop.
In fact I've never replaced an injector in a Cummins engine because of wear or mechanical failure. I did replace all six in a new engine once which is another story.
@Robobrainiac It's none of my business but let me caution you about "oversized injectors." Oversized injectors will perk a Cummins up but can be dangerous (read expensive). Do you have Boost and EGT gauges?
Let me tell another story. I bought my first ever diesel, an '01 Ram 3500 HO six speed in May 2001. I quickly heard of the TDR magazine and joined the TDR which was a great source of technical knowledge. As it happened, the TDR was holding a rally at a nice RV Park along I-10 near Boerne, TX in June or July so I registered. I attended and met some great people. One was Joe Donnelly, a prominent TDR member, technical writer, holder of a Ph.D. in Chemistry, and a Cummins diesel hotrodder.
Joe delivered a technical presentation at the rally in which he discussed replacing the factory 245hp injectors in the new 2001 Cummins HO enigne with "motor home" 275 hp injectors. I was impressed and spoke with Joe after his lecture. I bought a new set of 275hp injectors and Joe installed them in my Doidge in the parking lot. They made a huge difference in horsepower and acceleration of my Dodge as well as torque and hill-climbing ability when pulling a trailer.
BUT a very important BUT when I floored the throttle in any gear, Exhaust Gas Temperature immediately pegged my EGT gauge @ 1600°. The Cummins uses aluminum pistons. Aluminum melts at a temp above 1300°. The factory tuned engine is carefully tuned so EFT doesn't exceed 1300°.
Oversized injectors over fuel each cylinder at full throttle. If you use full throttle while towing a heavy trailer your EGT is almost certainly moving into a dangerous range. If you're pulling a long hard grade with a heavy trailer in tow you can easily burn a hole in a piston.
Now, after I've got your attention, I put 325,000 miles on that '01 Ram mostly pulling trailers. It was still running strong when I sold it. 150,000 of those miles were accumulated working as an RV transporter for Horizon Transport in Wakarusa, IN. The engine survived because I used judicious throttle and kept my eye on the EGT gauge when I was towing.
Horizon Transport is the country's largest RV transport company. Horizon delivers RVs and other vehicles across the US and into Canada. Join Horizon today!
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If you don't have gauges on the truck with oversized injectors start saving your money for an engine.