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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 29516
Experience:  GM Grand Master Technician 2007. 14 year experience.
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2011 lml duramax glow plugs wont cycle enough to cold start

Customer Question

2011 lml duramax glow plugs wont cycle long enough to cold start the truck. Truck has new plugs and module. They module cycles for 10 - 15 seconds but glow plugs don't light just get warm for 2 seconds. new glow plug module programed to ecu. Any thoughts on this?
Submitted: 1 year ago.
Category: GMC
Customer: replied 1 year ago.
Is there an ambient temp sensor for this glow plug system. or is it internal to the module?
Expert:  Gm Tech (Cam) replied 1 year ago.

Hi there, I am Cam. I am sorry to hear about this issue. Can you tell me if there are any codes stored?

Customer: replied 1 year ago.
No dtc's stored
Expert:  Gm Tech (Cam) replied 1 year ago.

OK, How cold is it where you are? Even cycling for 2 seconds should be enough to start the engine.

There are several sensors for temperature on and around the engine. No codes suggests its not an electrical issue. I do wonder though if it’s a fuel pump issue.

Customer: replied 1 year ago.
20 deg cel. i havnt checked fue pressure but did test glow plugs in vehicle. thet do not get hot just luke warm. this is second set of glow plugs. customer replaced them with autolite plugs first.Engine now has new gm plugs and module. What comtroled ambient temp signal for this module. As I am a Ford Master Diesel Tech and not fully understanding gm tem yet.
Expert:  Gm Tech (Cam) replied 1 year ago.

I'm in Alberta so yes, that cool. The glow plug system I will attach a document describing it. But I have my doubts its glow plugs. If they are coming on, even for 2 seconds and not setting codes, that does not seem like glow plugs. They hit 1000º in 2 seconds of operation.

My concern is actually a fuel concern. Does your scanner show engine data? Specifically the actual fuel rail pressure?

Expert:  Gm Tech (Cam) replied 1 year ago.

Glow Plug System Description

Glow Plug Operation

In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.

Control of the instant start system glow plugs is accomplished by a glow plug control module and 4.7 volt glow plugs, requiring 2 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control module (ECM) and the glow plug control module within a wide range to suit the engine's pre–heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre–glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault.

A normal functioning system operates as follows:

Turn the ignition ON with the engine OFF, and at room temperature.

The glow plugs turn ON and heat up in 2 seconds and then are pulse-width modulated (PWM) for another 2 seconds.

The glow plug wait lamp is ON for 1 second during cold start.

The glow plug wait lamp may not illuminate during a warm engine start.

If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.

The glow plug control module provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.

The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

Customer: replied 1 year ago.
what is the the desired fuel rail pressure for this engine when cranking?
Expert:  Gm Tech (Cam) replied 1 year ago.

Needs minimum 1450 psi or 10 mpa just to fire. If it does not get there, it will not fire injectors and that may be a fuel pump issue. Check that out and let me know what you get.

Customer: replied 1 year ago.
Hi Cam the truck will be back from calgary today. I will let you know finding then. Thanks for all infromation to this point. This system differs from the powerstroke system. I will also recheck for dtc's. this customer has his own code reader and clears dtc's. when his engine mil is present. Drives me crazy. I have the snap-on veris pro and pass through for Gm My Tech2 is not here yet as I purchased it 10 days ago. This customer also has a programer and egr delete installed in vehicle. could this ba a concern? I have tried and tested glow plug system with stock calibrations and bulley dog calibrations and it made no differance. So I will follow up with fuel delivery rail pressure as I understand where you are going with this. I agree as the powerstroke is simular in frp trouble. I Know customer had four glow plug dtc's before replacing the plugs first time. They have not been present while we have been working on this vehicle. Thanks for getting me outside the box in thinking terms.
Expert:  Gm Tech (Cam) replied 1 year ago.

No problem. Let me know when you get more info and I can respond then.

Expert:  Gm Tech (Cam) replied 1 year ago.

And yes the programmer may have done something. As you know it jacks up the pressure to get the power. My fear now is that a weak injection pump has taken out the fuel system ( I have one in my bay now replacing EVERYTHING in the fuel system ) for this exact issue.

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