Have an 05 f350 6.0 power stroke. 180k, has run fine for a long time and still does.
Only drive it a few times a month and usually for longer drives often towing a camper or car.
just drove it 2.5 hours relatively unloaded and noticed something different: the glow plugs ran for their usual 5-second or so session before starting right up. But had a few starts and stops during the trip and it was obviously all hot. Usually when it's hot the glow plugs light up for about 1/2 second and go out. But now they're staying on for about 2-3 seconds.
Everything is hot, it starts and runs fine, but why are the glow plugs running longer??? I know it can't be good but is it bad??
Iirc, it isn't spoke about, but just because the light goes out does not mean the relay and pcm are not working in conjunction to warm the chamber and cylinder up. I have heard upto 30 sec after cranking and randomly to check performance.
Now, as to your light, it could be the light itself, a worn through wire, a bad glow plug relay, or a funky pcm connection making the system run. Personally, I would replace the relay first, with an upgraded snow plow relay if it fits. Then probably dbl check the connections for everything and replace the bulb.
Hmmm. There is a glow plug control module and I wonder if that is what is acting up....
Ranger is right. The dash light does not correspond to GPR function. The light goes out telling you it's ready to start, but it leaves the plugs on during cranking. The cycling of the light is just a function of the ECM letting you know it's cycling, but it doesn't come on necessarily with the plugs themselves.
The dash light output is probably just an algorithm based on air temps, coolant temps, fuel temps, etc.
If you want to go really deep, hook a test light to the GPR output and you'll see what they're actually doing.
Edit to add: Adding that light is a good idea anyway to diagnose GPR failure. They'll get to a point where they click, but don't connect, but the dash light still cycles. If you ever get in and see the WTS, but not your added light, you know the GPR failed. The other way to diagnose if you have a no-start in the cold is to cycle the key and watch the volt meter. If you key on, wait for click, and the voltage drops more than 1v or so, it's probably good. If you key on, wait for click, and it moves so little that you can hardly tell, it's bad.
I'm going to guess a coolant temp sensor is going out. Engine likely used that to decide how long to keep the flow plugs on.
just a wag.
Here you go big homie. Straight from Mitchell.
The glow plugs are located in the cylinder heads, under the glow plug wiring harness.
The glow plugs are self-regulating. If the engine oil temperature is above 55°C (131°F), the PCM will bulb-check the WAIT TO START lamp but not energize the glow plug relay.
The glow plug ON time varies from 0-120 seconds depending on battery voltage, engine oil temperature and barometric pressure.
The glow plug ON time is independent of the wait to start lamp ON time.
The glow plug control monitor (GPCM) system is designed to find failed glow plugs or failed wiring in the glow plug system.
Fire up ye olde scan tool.
Check for codes.
Fix that stuff.
Check that sensor output for barometric sensor and oil temp sensor are reasonable based on current conditions.
Monitor oil temp during operation and runtime. 6.0 oil temp should be around 200F under normal operation and always be within 15 degrees of coolant temp. Note there is no gauge for oil temp, but for the HUEI injection system in the truck, it doesnt really care about coolant temp, the bulk of the decisions are made from oil temp.
