Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Port Fuel Injector Balance Test (SFI)
The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. All injectors should have a pressure drop of 1.5 psi (.11 kg/cm2 ) or less. If pressure drop is more or less than other injectors, replace appropriate injector.
- Turn ignition off. Connect Fuel Pressure Gauge (J-39021-301) to pressure tap. Unplug harness connector at all injectors. Connect Injector Switch Box (J-39021-210) to one of the injectors.
- Follow manufacturer's instructions when installing adapter harness. Ignition should be turned off at least 10 seconds to complete PCM/VCM shutdown cycle.
- Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
- Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize switch box one time and note pressure drop at lowest point.
- Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
- Repeat step 4) on each injector and compare pressure drop. Recheck injectors not within pressure drop range. Replace injector(s) failing second check. If injectors are all okay, plug in harness connectors and review SYMPTOMS in the TESTS W/O CODES article.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
Rather have a pro handle this?
A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.
No obligation. See pricing before you book.