I know what you are thinking, and the test is an actual test but the results do not reveal what you are thinking. Injector balance rates are a bit misleading, the test is conducted at idle pressure 30-35 MPA generally, which roughly translates to the lowest operating pressure of the system. So what is accomplished by these results obtained from the testing, and what do the test results really mean.

First, the results could indicate a fault that is not at all injector related, or it could potentially reveal a bad injector through coincidence, yes I said “through coincidence”. Let me explain what makes an injector “bad”, is excessive return rate, or is also termed as excessive back flow. When this condition exists, an injector will have to be rebuilt, or replaced period.

We have customers send in injectors that have balance rate issues, and on occasion, we have been able to re-calibrate them and put them right back into service. When we test an injector we are testing them at different operating points of pressure from idle to wide open throttle. The results from the testing determine different things. An injector can pass every test but one and need re-calibrating. Also conversely an injector can fail every test, and still provide equal output to a new injector in several of the tests. It will always be within spec at full throttle, as long as the system rail pressure will allow it to operate at that level.

So then what is the purpose, and what are indicators for the balance rate test. Typically white smoke at idle, is the major concern for emissions. As a general rule Diesel engines are the least efficient at idle for emission purposes. You may notice no operational issues, but just a slight haze at idle and have balance rate issues. I assure you that if you buy a good replacement injector, the issue will go away, but testing and a shim swap may have also possibly corrected the issue.

The balance rates are derived from crankshaft speed, it is possible a mechanical defect or even carbon build up could cause a deviance in the range of results. Let’s look a little closer at the specifications and consider the fuel volume variance that is being reported. We are dealing with cubic millimeters, or mm3. This measure of volume is on the level of micro drops. Consider 1 cubic centimeter, or 1 milliliter as they are equivalent volumes, which would translate to 1000 mm3. At 2 mm3 volume you have 0.04 the volume of a drop of water. 50 mm3 roughly equals a single drop of water. I am no scientist but from online charts I can reference the specific gravity between the two, water is at 1.0 and Diesel at 0.8-.096.

Technology is wonderful, but I find it quite impossible that balance rates can be accurate enough to discern these tiny volumes.

If you want to further discuss this, post on this blog.

Leave a Reply