Glow plugs no go?

NapaBavarian · **Joined:** Mon Jun 20, 2016 2:39 pm **Posts:** 129

Jeep is a little cold blooded and blows a cloud of smoke now that the temp are down in the mornings, summer I noticed the gp light only flashed on and off, now it doesn't come on at all, does it normally stay on for 6-8 seconds like most diesels when all is working properly? I found a few threads relating to this but nothing conclusive.

mass-hole · **Posted:** Mon Dec 19, 2016 1:29 am

NapaBavarian wrote:

Jeep is a little cold blooded and blows a cloud of smoke now that the temp are down in the mornings, summer I noticed the gp light only flashed on and off, now it doesn't come on at all, does it normally stay on for 6-8 seconds like most diesels when all is working properly? I found a few threads relating to this but nothing conclusive.

Yes it normally stays on for like 5-7 seconds.

If it's a rough start, takes a long time or all cylinders don't fire quite right, I will also get some white smoke

flash7210 · **Posted:** Mon Dec 19, 2016 9:40 am

If there was a problem with the glow plug system there would be a code set.

Exactly how cold is it?

WWDiesel · **Posted:** Mon Dec 19, 2016 10:19 am

NapaBavarian wrote:

Jeep is a little cold blooded and blows a cloud of smoke now that the temp are down in the mornings, summer I noticed the gp light only flashed on and off, now it doesn't come on at all, does it normally stay on for 6-8 seconds like most diesels when all is working properly? I found a few threads relating to this but nothing conclusive.

According to the FSM, the GP dash light only stays on for 1 sec till temperature drops to -10C at which time it will stay illuminated for 10 seconds.

This is how the glow plug logic works according to the FSM:
Please note, the Glow Plug light on the dash only illuminates for 1 second until the coolant temperature drops to -10C or below at which point the light on the dash illuminates for a full 10 seconds according to the control chart ...
Even though you will only see the light on the dash illuminate for 1 second (and you may miss it if you are not looking at it) the ECM continues to heat the glow plugs for up to 21 seconds after the dash light has only *blinked depending on the coolant temperature!

Seems like stupid logic, why not just illuminate the dash light for the entire period of time the glow plug is being heated? :2cents:

So, based on all of this; in cold weather, leave the ignition switch in the ON position for the entire period of time as listed in the chart below before trying to start the engine and it may alleviate some cold start issues...

From FSM: wrote:
Ignition Switch On (Engine Off)
When the ignition is turned on, the ECM activates the glow plug relay for a time period that is determined by engine coolant temperature, atmospheric temperature and battery voltage.
When the ignition (key) switch is placed in the ON position, a signal is sent from the sensors to the ECM relaying current engine coolant temperature and ambient air temperature (See Chart below:).
After receiving this signal, the ECM will determine if, when and for how long of a period the glow plugs should be activated. This is done before, during and after the engine is started. Whenever the glow plug module is activated, it will control the 7 volt high amperage circuit for the operation of the four glow plugs.

Pre- is heating time prior to engaging the starter motor, and Post- is heating time after the engine starts!

lacabrera · **Posted:** Mon Dec 19, 2016 11:16 am

The reason for the light not to remain on is we are all taught not to crank the engine over until the glow plug light goes out. As wwdiesel has mentioned the GP'S can operate for a few minutes with the engine running. Yes 1 sec is too short and easily missed.

NapaBavarian · **Joined:** Mon Jun 20, 2016 2:39 pm **Posts:** 129

Thanks, it is around 0°c +/- recently, I'll keep those glow times in mind. I guess jeep expected us to be psychic.

mass-hole · **Posted:** Mon Dec 19, 2016 11:43 am

WWDiesel wrote:

NapaBavarian wrote:

Jeep is a little cold blooded and blows a cloud of smoke now that the temp are down in the mornings, summer I noticed the gp light only flashed on and off, now it doesn't come on at all, does it normally stay on for 6-8 seconds like most diesels when all is working properly? I found a few threads relating to this but nothing conclusive.

According to the FSM, the GP dash light only stays on for 1 sec till temperature drops to -10C at which time it will stay illuminated for 10 seconds.

This is how the glow plug logic works according to the FSM:
Please note, the Glow Plug light on the dash only illuminates for 1 second until the coolant temperature drops to -10C or below at which point the light on the dash illuminates for a full 10 seconds according to the control chart ...
Even though you will only see the light on the dash illuminate for 1 second (and you may miss it if you are not looking at it) the ECM continues to heat the glow plugs for up to 21 seconds after the dash light has only *blinked depending on the coolant temperature!

Seems like stupid logic, why not just illuminate the dash light for the entire period of time the glow plug is being heated? :2cents:

So, based on all of this; in cold weather, leave the ignition switch in the ON position for the entire period of time as listed in the chart below before trying to start the engine and it may alleviate some cold start issues...

From FSM: wrote:
Ignition Switch On (Engine Off)
When the ignition is turned on, the ECM activates the glow plug relay for a time period that is determined by engine coolant temperature, atmospheric temperature and battery voltage.
When the ignition (key) switch is placed in the ON position, a signal is sent from the sensors to the ECM relaying current engine coolant temperature and ambient air temperature (See Chart below:).
After receiving this signal, the ECM will determine if, when and for how long of a period the glow plugs should be activated. This is done before, during and after the engine is started. Whenever the glow plug module is activated, it will control the 7 volt high amperage circuit for the operation of the four glow plugs.

Pre- is heating time prior to engaging the starter motor, and Post- is heating time after the engine starts!

I dont think this is how mine works. Mines sitting in my insulated garage overnight and I always get more than 1 second even when the temp is 45 or 50 in there, and i dont believe it stays on for a full 10 either.

WWDiesel · **Posted:** Mon Dec 19, 2016 2:09 pm

mass-hole wrote:

I dont think this is how mine works. Mines sitting in my insulated garage overnight and I always get more than 1 second even when the temp is 45 or 50 in there, and i dont believe it stays on for a full 10 either.

Anything is possible! Would not be the first time we have discovered that there are errors contained in the FSM.... :roll:

Glow plugs no go?

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