The easy but expensive (about $900) route is to replace the PCM (Powertrain control module, AKA computer located in the battery box). At below 30 deg. F, found the PCM wasn't firing the injector even though the injector resistance was within the specified range (12 ohms). To repair without replacing the computer, we used a 12 V lamp (#194) to monitor the injector activity by placing it in parallel at the injector. Interestingly, because of the increased current the output of the PCM is now working reliably. The resistive component of the lamp may be a contributing factor to this solution.