Common Rail FAQ

Let’s begin a real world education about Bosch Common Rail Injectors. The biggest problem we run into is the lack of knowledge and experience in our customers, both in repair shops and “do it yourselfers.” They fail to address the cause of failure, correct diagnosis, and proper repair procedures. The result is the unnecessary spending of money.

1. The World Wide Web:
The web is your greatest asset and your worst enemy. Just because someone has a good website designer is not a good reason to do business with them. Your best defense is look for the Bosch Logo Bosch Logo and remember that good qualified Bosch trained techs are not likely to have the time to talk on the web. They have REAL jobs! It is also important to realize that these sites are trying to obtain your money!
2. Injector Upgrades:
There are no Bosch injector upgrades. Bosch designs each injector configuration for each application, taking into consideration all design parameters. Installing larger nozzles does not magically cause the whole engine to change design. Another thing to know is that you cannot install nozzles yourself without affecting the injector internal dimensions. This has to be set up at time of assembly using Bosch Assembly and Measuring Equipment and then tested on a Bosch Common Rail Test Machine. The measurements are in microns and are measured using computer controlled, pneumatically applied gauges and a torque wrench that has software and gyros in it to measure torque, rate and angle of torque. The software changes with each type of injector. It is that critical! Also, there is no test plan in existence to run on the injectors, so…good luck! We could take two rebuilt Bosch injectors and swap the nozzles from one to the other and it will not pass the test bench. Think about it! This is the sort of thing that damages pistons. If you have plenty of money and want to go fast, have fun! But the most common scenario is a pick-up that needs a $15,000 engine rebuild with $30,000 still owed on the loan.
3. Proper Diagnosis:
If you don’t have the factory scanners to read these systems, get them or find someone who has them. You also must be able to measure pressures, volume and fuel returns. I can’t say enough about how important fuel return is. It is directly linked to injector ball and seat wear. A contaminated system will destroy the seats. Improper diagnosis causes you to replace the wrong parts and spend money!
4. Contamination:
Contamination of your system is the number one cause of failure in common rail systems. When debris gets in between the ball and seat it acts like a water jet laser and cuts the metal, damaging the seat. When you find contamination it is so important to clean the whole system. Nothing is more heart breaking than buying a set of injectors and one week later the replacement injectors are junk too!

[Click on images for larger picture.]
Clean Contamination Contamination Contamination

You must replace the head connectors, clean the fuel tank (off of the truck), replace the high pressure pump, the fuel rail, and clean everything.

Contamination Contamination


A real good indicator of contamination is to look at the outside of the fuel connectors (Dodge). If dirt or water is here, the fuel in this area comes out of the injector return hole to fill this void in the cylinder head; it has been through the injector completely. OUCH!

5. Read the Book:
Don’t depend on advice from friends or the internet to find torque specs, troubleshooting, and assembly procedures. Use the manufacturers’ service manuals or automotive software like AllData, Mitchells, etc…and there is training available for all brands of diesel engines. Call us and we will point you in the right direction. The best advice for the do it yourselfer is to find a qualified shop that has all the necessary equipment and a heavy presence in the diesel industry.