ERIKC DLLA153P977 fuel pump denso injector nozzle DLLA 153P 977 Injectors spray nozzle DLLA 153 P977

FAQ: Increase or Decrease in Long- and Short-Term Fuel Trims

ERIKC Answer:The fuel calibration curves in the Powertrain Control Module (PCM) are based on OEM dyno testing using a new engine. Fuel pressure is within a specified range for that engine, and the injectors are all clean and new. The PCM’s built-in adaptive fuel control strategies allow it to adjust both short-term and long-term fuel trim to compensate for variances in fuel pressure and fuel delivery to maintain the correct air/fuel ratio — but only within certain limits.

FAQ: Not Enough Resistance

ERIKC Answer:The solenoid at the top of the injector creates a magnetic field that pulls up the injector pintle when the injector is energized. The magnetic field must be strong enough to overcome the spring pressure and fuel pressure above the pintle, otherwise the injector may not open all the way. Shorts, opens or excessive resistance in the injector solenoid can also cause problems.

Typically, the solenoids often short internally when injectors fail, which causes a drop in resistance. If the specification calls for 3 ohms, for example, and an injector measures only 1 ohm, it will pull more current than the other injectors. Too much current flow to an injector may cause the PCM injector driver circuit to shut down, killing any other injectors that also share that same driver circuit. One way to check the injectors is with an ohmmeter.