Method 1: The "Listen" Test (Least Reliable)
* Procedure: With the engine running, carefully listen near each injector. You should hear a distinct clicking or ticking sound. If an injector is completely clogged or not firing, you'll likely not hear anything from that location.
* Limitations: This method is highly unreliable. A faint sound might still mean low fuel pressure or a weak injector. A clicking sound doesn't guarantee the injector is spraying correctly. Background engine noise can make it difficult to hear the injectors.
Method 2: Fuel Pressure Test (More Reliable)
* Procedure: This involves checking the fuel pressure at the fuel rail with a fuel pressure gauge. You'll need a fuel pressure gauge adapter that fits your Bronco II's Schrader valve (usually located on the fuel rail). Consult your repair manual for the correct fuel pressure specifications for your engine. Low fuel pressure can cause injectors to not spray properly, even if they are good.
* Limitations: This test doesn't directly test the injectors themselves, but it helps rule out low fuel pressure as the culprit. If the pressure is low, you'll need to diagnose the fuel pump, regulator, etc., before moving on to injector testing.
Method 3: Injector Pulse Test with a Noid Light (Most Reliable)
* Procedure: A noid light is a small tool that plugs into the injector's electrical connector. It's designed to test if the injector is receiving the electrical signal from the Engine Control Unit (ECU). With the engine cranking or running, the noid light should flash for each injector. If it doesn't flash, the injector isn't receiving the signal. However, a flashing light does *not* guarantee that the injector is spraying fuel correctly.
* Advantages: This is the best way to determine if the ECU is sending the signal to the injector.
* Limitations: It does not test fuel flow or spray pattern. A bad injector can still receive the signal and not spray properly. You still need to consider fuel pressure.
Method 4: Injector Flow Test (Most Thorough but Requires Specialized Equipment)
* Procedure: This is the most comprehensive test, requiring a fuel injector tester. This device connects to each injector, allowing you to see if the injector is flowing fuel at the proper rate and pattern. It measures the amount of fuel delivered during a specific pulse.
* Advantages: This definitively tells you if an injector is functioning correctly.
* Limitations: This method requires specialized and relatively expensive equipment.
Important Considerations:
* Safety: Fuel is flammable. Work in a well-ventilated area, away from open flames. Wear safety glasses.
* Repair Manual: A repair manual specific to your 1990 Bronco II is essential. It will provide detailed instructions, specifications, and diagrams.
* Professional Help: If you're not comfortable working on your vehicle's fuel system, take it to a qualified mechanic. Improper fuel system work can be dangerous.
In short, the "listen" test is a quick check but unreliable. The noid light test is a good intermediate step. Testing fuel pressure is important to eliminate that possibility. The ultimate test requires an injector flow tester. Start with the simpler tests and proceed to more advanced tests as needed. Remember safety first!
