Why does the glow plug flash on a 2004 Isuzu truck when the engine is already running?

Answer 1

Well in 2004 their were 2 engines produced so assuming you have the older model which is the 4.8L 4HEISX with mechanical style injection pump. The glow plug light has 2 functions for those years. Its typical function to inform the driver to wait before cranking the engine while the glow plugs heat up the air in the combustion chamber. And the 2nd function is your ENGINE LIGHT. The 4HEISX engine uses mechanical fuel delivery which contains very few sensors, electronic components "talking" to the ECU. Many of the components on the engine is vacuum operated so no sensors are used. In my experience (10yrs) that light doesn't come on that much and every time I have made a repair to stop the light from blinking it has been related to the injection pump's pre-stroke and or rack sensor wiring. THese 2 sensors have to do with timing and fuel delivery for the injection pump. Inspect the wiring that runs from the back of the engine forward to the pump for chaffing. One other area that i've seen have issue on that model is the engine speed sensor (RPM sensor as Isuzu calls it in parts catalog) wiring chaffing as well. It's located left rear of engine . If its running rough,white smoke,rolling idle I's say it is a problem with the pump's pre-stroke or rack sensor (to repair the sensors the pump needs to be sent out to a repair shop that does injection pump repairs because the sensors need to be calibrated and adjusted) If it's running good no driveability issues then it's a malfunction of one of the very few sensors this engine has. Not many things "electronically" goes wrong with this model due to the lack of electronics involved to make it run. Hope this helps get the codes pulled and go from their. I just about bet it's pump related. Good luck.