After cleaning and testing injectors if the results are not perfect, some wonder if the injectors Ok to use? Here are the basics.
Port Injectors:
- Flow Variance (CC/Min or LB/hr for Port injectors) (GDI Test reports for GDI/Piezo)
- An acceptable average fuel injector flow variance across a set of injectors is typically:
Within 2–3% for high-performance or racing engines
Within 5% for OEM or general street use
- Breakdown:
0–2% variance: Excellent matching, ideal for performance tuning and consistent combustion.
2–5% variance: Acceptable for most OEM applications and everyday vehicles.
5% variance: Often considered excessive and may lead to poor fuel economy, misfires, or emissions issues.
Leak Testing
Injectors should not leak when closed under fuel system pressure.
A leaking injector can cause hard starts, flooding, or engine misfire.
Electrical Performance
The injector’s resistance (ohms) should be within manufacturer specifications.
Irregular readings can indicate coil failure or short circuits.
Spray Pattern (ONLY APPLICABLE TO PORT INJECTORS)
The spray pattern should be fine, even, and conical without distortion or heavy drips.
Irregular spray patterns suggest clogging or internal damage.
- For any engine management system using sequential fuel injection, tighter matching helps ensure each cylinder gets the correct air-fuel ratio.
GDI Piezo Injectors:
- Some of the above is applicable however looking at the test results is key, Injectors are designed to operate within a specific flow corridor and things like spray pattern are meaningless. If your GDI/Piezo injectors show red it does not mean they are not usable it depends how far outside the norm they are and the intended use. If they are far out side then it is perhaps best to replace them. What is too far? We do not say and can not say. It depends.
Understanding GDI/Piezo Results
Bottom Line:
- We do not provide recommendations on whether to use injectors after the service based on the results. Our role is to clean the injectors and present the test results. Based on those results, the customer can choose to either continue using the injector or replace them based on their needs and understanding. When an injector is clearly failed we will tell you. When an injector hasn’t failed but shows less-than-ideal performance in one or more tests, it’s up to the customer to decide how to proceed based on their specific circumstances.