Corvette Magazine

LEFT: An electronic fuel injector is actually a solenoid valve. When the coil is energized, it pulls the "valve" open against spring and fuel pressure. The injector is turned "off" when current is no longer applied to the coil. This is a pintle style injector, but ball and disc type injectors function the same way. (The spring that fits between the coil and injector body is not shown.)

width accordingly. As a result, excess fuel will be delivered, the engine will run exceptionally rich, and both performance and fuel economy will suffer.
An injector/PCM mismatch can be difficult to diagnose because part throttle operation may not be affected. If the amount of correction required is within the PCM’s capability, a 14.7:1 air/fuel ratio will be maintained once normal operating temperatures are reached. The excessively rich condition will occur only following cold start and at wide

self-correction. But when an accelerator pedal is pushed close to the floor, "Learn Control" is turned off (O2 sensor input is ignored) and fuel flow is controlled by values in the fuel table contained in the PROM. One of the reasons some cars run extremely well at part throttle yet stumble or hesitate at or near wide open throttle is that the basic calibration is incorrect and once the ECM or PCM stops monitoring O2 sensor input, no correction is being applied.
So long as stock injectors are retained, air/fuel ratio at wide-open throttle should be relatively close to meeting engine requirements. However, when injector size is changed, and the PROM or PCM is not recalibrated, trouble is lurking beneath the hood. For good reason–the right hand doesn’t know what the left hand is doing.
As an example, LT1 engines were originally equipped with 24-pound per hour injectors. All is wonderful so long as the engine’s demand for fuel doesn’t exceed the injector's delivery capacity. But if extensive modifications are made, it’s necessary to increase injector size. Typically, 30-pound injectors are the first step up because they’re readily available and economically priced. Unfortunately, unless the PCM is recalibrated to reflect the change in injector size, it thinks 24-pound injectors are still in place and determines pulse