A restriction of only 8% to 10% during a single fuel injector can lean out the fuel mixture and cause a misfire. When this happens, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multiport systems that fireplace the injectors simultaneously, the pc compensates by increasing the “on” time of all the injectors, which may create an excessively rich fuel condition within the other cylinders.
Direct fuel injectors are more sensitive to restrictions due to the precise amount of fuel they inject into the combustion chamber.
3. Increase or Decrease in Long- and Short-Term Fuel Trims
The fuel calibration curves within the Powertrain Control Module (PCM) are supported by OEM dyno testing employing a new engine. Fuel pressure is within a specified range for that engine, and therefore the injectors are all clean and new. The PCM’s built-in adaptive fuel control strategies allow it to regulate both short-term and long-term fuel trim to catch up on variances in fuel pressure and fuel delivery to take care of the right air/fuel ratio — but only within certain limits.
The PCM might not be ready to increase injector duration enough to offset the difference if:
• An injector becomes clogged with fuel varnish deposits and fails to deliver its normal dose of fuel when it’s energized, or
• Fuel pressure to the injector drops below specifications due to a weak fuel pump, plugged filter, or leaky fuel pressure regulator.
This can leave the air/fuel mixture too lean, causing the cylinder to misfire.
4. Not Enough Resistance
The solenoid at the highest of the injector creates a magnetic flux that pulls up the injector pintle when the injector is energized. The magnetic flux must be strong enough to beat the spring pressure and fuel pressure above the pintle, otherwise, the injector might not open all the way. Shorts opens or excessive resistance within the injector solenoid also can cause problems.
Typically, the solenoids often short internally when injectors fail, which causes a drop in resistance. If the specification involves 3 ohms, for instance, and an injector measures just one ohm, it’ll pull more current than the opposite injectors. an excessive amount of current flow to an injector may cause the PCM injector driver circuit to pack up, killing the other injectors that also share that very same driver circuit. a method to see the injectors is with an ohmmeter.
5. Heat Soak
When the engine is shut off, the injectors undergo heat soak. Fuel residue evaporates within the injector nozzles, leaving the waxy olefins behind. Because the engine is off, there’s no cooling airflow moving through the ports and no fuel flowing through the injectors to scrub it away, so heat bakes the olefins into hard varnish deposits. Over time, these deposits can build up and clog the injectors. albeit a vehicle has low mileage, short drive cycles, and increased heat soaks can clog the injector.
Since the formation of those deposits may be a normal consequence of engine operation, detergents are added to gasoline to assist keep the injectors clean. But if a vehicle is employed primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away. On four-cylinder engines, the No. 2 and No. 3 injectors are within the hottest location and have a tendency to clog faster than the top injectors on cylinders No. 1 and No. 4. an equivalent applies to the injectors within the middle cylinders in six- and eight-cylinder engines. the warmer the situation, the more vulnerable the injector is to clogging from heat soaks. Throttle body injectors are less susceptible to heat soak due to their location high above the manifold plenum.
Heat soak can affect direct-injection injectors thanks to their placement within the head. Even with the upper pressures, the orifices can become clogged over time.
6. Failed Balance Tests
If you think that an injector is clogged or malfunctioning, an injector balance test can isolate the bad injector. Scan tools that will disable injectors can isolate an injector for diagnostics. Engine rpm drop might not be an efficient diagnostic method when performing a cylinder balance test where an injector is disabled.
A simpler method is watching the voltage changes from the O2 sensor. Leaking injectors and a few dead injectors are often missed even when an injector is disabled. Other problems with the ignition and mechanical components also might not show an rpm loss when an injector is turned off. If an injector is sweet, the voltage from the O2 sensor will drop to or below 100mV. If the matter may be a closed or dead injector, the long-term fuel trim may have compensated enough in order that the voltage doesn’t change.
Another effective test is to live the pressure loss within the fuel rail when each injector is fired and pulses for a group period of your time. Use an electronic injector pulse tester for this. As each injector is energized, a fuel pressure gauge is observed to watch the drop by fuel pressure. The electrical connectors to the opposite injectors are removed, isolating the injector being tested. The difference between the utmost and minimum reading is that the pressure drop.
Ideally, each injector should drop an equivalent amount when opened. A variation of 1.5 to 2 psi or more is cause for concern. No pressure drop, or a really low drop, maybe a sign the orifice or tip is restricted. a better than normal pressure drop indicates an upscale condition that would be caused by a stuck plunger or worn pintle.
7. Misfire Codes
A lean misfire may trigger a misfire code and switch on the check engine light. The code often is going to be a P0300 random misfire code, otherwise, you may find one or more misfire codes for individual cylinders, counting on which injectors are most affected.
8. Longer Crank Times
An injector leak will cause the rail to lose pressure while the vehicle is sitting leading to an extended than normal crank because the rail will need overtime to pressurize.
A normal crank time during a diesel common-rail injection system is typically around three to 5 seconds. this is often how long it’ll take the common-rail pump to create fuel pressure to the “threshold.” The fuel rail pressure threshold for cranking occurs around 5,000 psi. Normal common-rail systems will operate at 5,000 psi at idle and may reach up to 30,000 psi at wide-open throttle.
9. Lack of Maintenance
If an owner has neglected maintenance services like oil changes and filter replacements, the likelihood is that the fuel injectors will suffer. For port fuel applications, not changing the oil may result in blowby and a compromised PCV system, which builds up contaminates on the tip of the injector. Not changing the oil during an engine with a direct fuel injection system may result in a worn fuel pump camshaft lobe.
10. Vehicle Won’t Start With Full Tank
Major symptoms of contaminated fuel can include cranking no-start, hard starting, stalling, loss of power, and poor fuel economy. Because symptoms of fuel contamination generally appear immediately after refueling, the fuel indicator needle pegged on full should be a diagnostic red flag. Remember to ask if the vehicle has recently been refueled because some drivers just add fuel instead of topping off their tanks.