Things Are Not Always As They Seem

When OEM Isn’t OEM

We recently had a customer come into our shop for injector testing. He was working on a popular Japanese brand of an excavator that had over 16,000 hours on it and had taken the cylinder head off for unrelated repairs. The engine in this particular machine is a large, American brand. The cylinder head was removed, rebuilt, and put back onto the engine. Because of the hours on the machine and the work being performed, the mechanic decided to replace the injectors at the same time. He purchased the injectors from the manufacturer’s certified parts supplier. At this point, he has done everything by the book.

The problem

So, why is he here? He has a reman head on the engine and remanufactured injectors from a very reputable source. He told us that the engine ran fine for about twenty seconds, then started billowing huge clouds of black smoke, and he shut it down after a further 10 – 15 seconds. He feared the worst, so he did another compression test. The compression was great. The customer is then doing what all humans do, starting to wonder if he somehow contaminated the fuel system or installed them incorrectly. He brought the fuel injectors into our facility so we could perform tests that would either confirm or eliminate his concerns.

Testing the common rail injectors

The injectors in this particular engine application are originally Bosch injectors. We are proud to have the certified Bosch equipment to test this injector. Each injector is tested in five or six different stages, including an initial pressure test to confirm it is not leaking, as well as idle, mid load, heavy load, pilot injection, and possibly others depending on the application. Both fuel delivery and return flow are measured at each stage.

bosch fuel injector tester

Certified Bosch Injector Tester

We proceeded to test the injectors for the customer. After testing all six injectors, we found the following:

  • Two injectors passed without issue.
  • Two injectors were over-fueling at heavy and mid load. Since these were injectors fresh out of the box, this was somewhat concerning.
  • Two injectors were a major failure with extreme over-fueling (60 – 70%) at all test levels. Return flow was also far above spec.

So now the customer is faced with a conundrum. He knows his injectors are the problem, which is partially good news because he knows the cylinder head does not have to come back off. However, he doesn’t know if he received defective product, or if he is the culprit by accidentally contaminating the fuel system. He’s a competent mechanic with years of experience, but doubt creeps in. He decides to purchase another set of injectors from the original supplier. He will bring those directly to us, have them tested, and that should give him a pretty good idea of what is going on here.

Testing OEM Replacement injectors

The next day the customer returns directly from the OEM (original equipment manufacturer) with six replacement injectors in sealed bags. The results of this second round of testing was as follows:

  • One injector had very high return flow. Typically a remanufactured injector should have a return flow of about 20 – 25 mm3 on this test. The maximum flow rate limit is 66 mm3. This injector was measured flowing at 150 mm3!
  • The other five injectors were over-fueling by 5 – 10%.

The latter five will run an engine, but the computer will always be trying to adjust and compensate for the differences. The engine may have a hazy exhaust at idle, or if equipped with a Diesel Particulate Filter (DPF), it will clog up with carbon much faster than expected. The good news is now the customer knows the issue is with the replacement parts, and not with the installation.

Upon hearing of the results of the second set, the customer asks us; “Why is this the case? I bought these injectors directly from the equipment dealer’s parts department! Why would the injectors that you supply be any different?”

The difference between OEM and Bosch-built injectors

The injectors sold by the OEM dealer were NOT Bosch built injectors. We can tell this right away because all the logos and numbers were removed (as required by law). These injectors were assembled in an unauthorized facility. People generally think “Company ‘X’ is a huge, multi-national, well-known manufacturer who builds fantastic engines, so the replacement parts they are supplying must be great! Right?” We now know this is not always the case.

The customer went back to the OEM parts supplier and explained what was going on. The supplier refunded the customer for all twelve injectors, as well as covered the testing charges here at our facility, which was some great customer service on their part and truly the right thing to do.

Our technician was curious and decided to test the replacement injectors that we received from Bosch – they passed with flying colors, as expected. To compare, we also decided to test one of the customer’s old worn injector cores – one that had 16,000 hours on it. It flowed about 10% low under heavy load, but passed all testing otherwise. With 16,000 hours of runtime, the old injector was still almost as good as the reman OEM injectors the customer had purchased from the dealer!

This article is not to sling mud at anyone. It is simply a real-world example to show that even though this customer has done absolutely everything by the book, sometimes you still have issues. It is unfortunate the quality control from the OEM injector rebuilder is not better, but in all honesty, they should have just left the rebuilding of these parts to Bosch or Bosch certified facilities that have the tools and training to build the injectors correctly.

I think we can now more clearly understand why Bosch simply will not stand for misrepresentation of their products. A common rail injector is a very complex part that plays a critical role in the operation of your engine. The exacting tolerances required to build an injector properly are extremely precise, and the building/rebuilding of them should be left to the people that have the factory support, specialized equipment, and training to do it right.

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