Things Are Not Always As They Seem

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.

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?”