What is the allowable percentage of deviation between a known good injector and a bad one? (PSI drop in an injector balance test).

Test: Turn key, record primed primed fuel pressure, pulse injector 50 times, 7ms width, record new fuel pressure. Repeat 7 more times. (ran test twice)

Cyl #, primed PSI, after test PSI, drop %
1 - 41 - 28 - 31.70
2 - 41 - 28 - 31.70
3 - 41 - 28 - 31.70
4 - 41 - 30 - 26.83
5 - 41 - 28 - 31.70
6 - 41 - 28 - 31.70
7 - 41 - 26 - 36.58
8 - 41 - 28 - 31.70


So Injectors 7 and 4 are off, one 5% high, other 5% low. But is 5% allowable? Maybe this is a question for southbay since they are the ones with the equipment and test procedures

 

The data presented appears to show injectors flowing at different rates. However, the accepted (and more reliable) method for testing is to maintain an operating rail pressure during the course of the test, pulse injectors for a given period and number of times (as you have done) and capture the fuel to be measured in a graduated cylinder. In other words, measure flow, not pressure drop. This eliminates any flow variation due to propagation delay at varying pressure (which is not linear) reveals the actual flow rates of the injectors.

My suspicion is that your testing is sufficient to indicate a problem, but sending off the injectors for cleaning, testing, and flow-matching seems to be in order. This can be done by several injector service companies.

A second method to verify a flow mismatch would be to perform an operational injector power balance test. With a hot engine, disable the IAC, then connect a diagnostic tachometer (not the in-dash thing). Note the RPM drop for each cylinder as each injector is unplugged, one at a time. Reconnect the injector then move on to the next one. Of course, this only works if everything else is in good working order, such as ignition, compression, and air flow.

 

We flow our injectors both static and dynamically. Static is a straight wide open flow at 100% duty cycle. Dynamic flows the injector throughout the operating range from 600rpm to 10,000rpm from 3ms-12ms at a time test....Best way to match injectors. The ECU should compensate for the 5% deviation. When we match our injectors they flow 1% or less.