Injector balance rates are fuel adjustments by the engine or fuel injection control module for each cylinder to balance out the motor. Fuel is either removed or added to each cylinder to help the engine run as smooth as possible. Ideally, balance rates should be very similar between each cylinder. Big deviations between cylinders indicate an issue with that specific cylinder. Balance rates can be used to identify faulty injectors, but can indicate other non-fuel related problems as well.
Utilizing Balance Rates for Diagnosis
The balance rate adjustments are utilized by the control module only at idle. A positive value indicates that fuel is being added to the cylinder, while a negative value indicates that fuel is being removed from the cylinder. GM specifies that the balance rate should be no more than +4 or -4. The maximum balance rate number is +/- 15.
How to Check Injector Balance Rates
Using a GM scan tool, Edge CTS monitor, or equivalent, perform the steps below.
- Start and run the engine until the engine coolant temperature is more than 180°F.
- Turn OFF all accessories.
- With the transmission in park and at idle, note the Balance Rates for all 8 cylinders from the scan tool.
Conclusion
If an injector is either removing or adding too much fuel to a cylinder, there is likely an issue with that cylinder since the control module is trying to compensate. Balance Rates will not always provide an accurate diagnosis of injector performance due to many variables that affect the calculation. If a balance rate is really high, most of the time it is not the fuel injector itself. Other issues that can affect balance rates are blown head gaskets, cracked cylinder heads, leaking valves, cracked pistons, damaged piston rings, broken crankshaft or even a cracked engine block. We highly recommend performing a compression check to confirm there aren't mechanical issues. Checking the injector balance rates when diagnosing a fuel system concern is a good start, but it should not be the only deciding factor.
