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420 Posts
Discussion Starter #1
My truck is in its 5th winter. I never plugged it and it always started very well even in the coldest mornings.

Since 3-4 days, It won't start on the first crank, it will take 5-10 times to do it and it idles like a wood chipper for a few minutes "when" it starts.

Here are the facts:

- Brand new batteries last fall
- Changed fuel and air filters just to make sure
- Winter blend fuel with cetane booster additive like always
- No "check engine" light
- Tried to cycle the glow plugs 3-4 times before cranking with no effect
- Once hot, truck runs like a champ, lots of power like always

I can cycle the plugs 25 times and the batteries never seem drained but I never saw the check engine light and from past posts, if the plugs don't work, codes are set.

Ant ideas?

3,049 Posts
I'm not sure if you will get a code or not BUT if your batteries aren't losing voltage when the glow plugs are supposed to be on then there not working.

It could either be a few or all of the glow plugs or it could be the glow plug relay which is what turns them on and off.

I would start with the relay and see if there is any voltage going to it and if there is any voltage coming out of it when the plugs should be on.

If the glow plugs don't work it is very difficult to start these trucks in colder weather.



16,610 Posts
It could also be the intake heater not working. It should be pretty easy to diagnose both systems with a volt meter when it is cold.

420 Posts
Discussion Starter #4
How can I check the intake heater and where is the relay located?

Thanks for the inputs...

The only thing that bugs me is the absence of codes...

16,610 Posts
Hard Start

DEFINITION: The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but immediately dies.

Preliminary Inspection
Refer to Symptoms - Engine Controls .
Ensure the driver is using the correct starting procedure.

Sensor Inspection
Inspect the engine coolant temperature (ECT) sensor. Use the scan tool to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself.
Turn ON the ignition with the engine OFF. Observe the actual fuel rail pressure with a scan tool. The actual fuel rail pressure should be between 1.0-1.8 MPa. If it is not, inspect for high resistance in the fuel rail pressure (FRP) sensor circuits or the FRP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Inspect the crankshaft position (CKP) sensor reluctor wheel. Remove the CKP sensor and attempt to move the reluctor wheel front to back or side to side with a probe. If there is any movement the reluctor wheel retaining bolts are loose.

Fuel System Inspection
Inspect the fuel pressure regulator 12-volt circuit for an intermittent short to ground. Observe the FRP Command percent while cranking. A range of 85-95 percent indicates a possible short to ground condition.
Start the engine and command the fuel pressure to 160 MPa with a scan tool. If the actual fuel pressure does not reach 160 MPA, perform the Fuel System Diagnosis - High Pressure Side .
Inspect the fuel supply to the fuel injection pump. Refer to Fuel System Diagnosis .
Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis .
Inspect for air in the fuel system. Refer to Fuel System Diagnosis .
Inspect for external fuel leaks. Refer to Fuel Leaks .
Inspect for high engine oil level. Refer to Fuel in Engine Oil in Engine Mechanical - 6.6L.
Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .
At idle observe the FRP Regulator Fuel Flow Command parameter with a scan tool. If the FRP Regulator Fuel Flow Command is more than 2700 mm³, perform the Fuel System Diagnosis - High Pressure Side .
Inspect the fuel tank cap vent for proper operation.

Electrical System Inspection
Inspect the glow plug system for proper operation. Refer to Glow Plug System Diagnosis .
Inspect for a slow cranking speed. Refer to Symptoms - Engine Electrical in Engine Electrical.

Air Intake System Inspection
Inspect the air cleaner and air intake ducts for a restrictions or leaks.
Inspect for a restriction in turbocharger inlet duct.
Inspect for a restriction or a leak in the intake manifolds.

Exhaust System Inspection
Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust in Engine Exhaust.

Engine Mechanical Inspection
Inspect the engine for the following conditions:

Improper valve timing
Bent pushrods
Worn rocker arms--Refer to Valve Rocker Arm and Shaft Cleaning and Inspection in Engine Mechanical - 6.6L.
Low engine compression--Refer to Engine Compression Test in Engine Mechanical - 6.6L.
Broken or weak valve springs
Worn camshaft lobes--Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical - 6.6L.

Additional Inspection
Inspect for an intermittent CKP signal. Refer to Intermittent Conditions .
Compare the scan tool data at idle with the scan tool data list. Refer to Scan Tool Data List .
Inspect the Service Bulletins for control module software updates.

16,610 Posts
Glow Plug System Diagnosis

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=737347&evc=sm&pubid=271&cellId=63721&mspsdsubkey=2064#ss1-737347">Circuit Description

The glow plug system is used to assist in providing the heat required to begin combustion during engine starting at cold ambient temperatures. The glow plugs are heated before and during cranking, as well as during the engine operation. The engine control module (ECM) controls the glow plug ON times by monitoring coolant temperatures and glow plug voltage. This system check will check the glow plugs and the glow plug feed circuit coming from the relay/controller.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=737347&evc=sm&pubid=271&cellId=63721&mspsdsubkey=2064#ss2-737347">Diagnostic Aids

If the glow plug relay or controller is stuck in the ON position, check for proper operation of the glow plugs. When the glow plugs are commanded ON by the scan tool, an internal engine control module (ECM) timer protects the glow plugs from damage by cycling them ON for 3 seconds and then OFF for 12 seconds. Most glow plug system failures are covered by DTC P0380. If no DTCs are stored, the vehicle is hard to start and white smoke is present during cranking or after the vehicle is started, the most likely cause of failure is the glow plugs.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=737347&evc=sm&pubid=271&cellId=63721&mspsdsubkey=2064#ss3-737347">Test Description

The numbers below refer to the step numbers on the diagnostic table.
  1. <LI value=2>This step will make sure there are no other DTCs stored that will affect the operation of the glow plug system.
    <A name=TD3><LI value=3>This step will check each glow plug for an open.
    <A name=TD4>
  2. This step will check each glow plug feed circuit for an open.
Schematic Reference: Engine Controls Schematics
Connector End View Reference: [URL="http://service.gm.com/servlets/CellHandler?CellId=63610&RefDoc=737347&evc=sm"]Engine Control Module (ECM) Connector End Views
or Engine Controls Connector End Views
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls
Are DTCs P0117, P0118, P0380 stored as history or current codes?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 3
  1. <LI type=1>Turn OFF the ignition. <LI type=1>Disconnect all the glow plugs.
  2. With a test lamp connected to battery voltage, probe the spade terminal on each glow plug.
Do all glow plugs illuminate the test lamp?
Go to Step 4
Go to Step 9
  1. <LI type=1>Turn ON the ignition, with the engine OFF. <LI type=1>Verify the glow plugs are still disconnected. <LI type=1>Probe each glow plug supply voltage circuit with a test lamp connected to ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.
  2. With a scan tool, command the glow plugs ON.
Does each circuit illuminate the test lamp?
Go to Step 5
Go to Step 10
Does the test lamp illuminate all the time for each glow plug terminal, even when the glow plugs are not commanded ON?
Go to Step 6
Go to Step 11
  1. <LI type=1>Disconnect the glow plug supply voltage connection from the glow plug relay.
  2. Probe each glow plug terminal with a test lamp connected to ground.
Does the test lamp illuminate for all terminals?
Go to Step 7
Go to Step 8
Repair the short to voltage on the glow plug supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 11
Replace the glow plug relay/controller. Refer to Glow Plug Relay Replacement .
Did you complete the replacement?
Go to Step 11
Replace all glow plugs that do not turn ON the test lamp. Refer to Glow Plug Replacement - Bank 1 or Glow Plug Replacement - Bank 2 .
Did you complete the replacement?
Go to Step 11
Repair open in each circuit that does not turn ON the test lamp. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?
Go to Step 11
Operate vehicle within the conditions under which system fault was noted.
Does the system operate properly?
System OK
Go to Step 1

420 Posts
Discussion Starter #7
Thanks MaxPower,

I can't seen the diagrams that could show me the position of the relay etc. from reading the article I can add this to my facts:

- White smoke present during cranking
- When cranking, the engine "wants" to start every 3-4 seconds but ultimatly returns to cranking. This "cycle" goes on for almost 30 seconds and then it starts.

So it seems related to the plugs and probably not only one or two of them but the whole circuit. I can see the presence of a fuse in the fuse diagram but can't find the fuse itself.

Will begin to check that in the morning.

218 Posts
I'm having the same type of problem once in awhile. My truck sits in a heated garage. If I start it and back it outside into the cold air and keep going, it's all ok. However, if I stop in front of the garage to wait for someone to come out [wife and three teenage daughters- take your pick] and I put the truck back in park, the engine will stumble for a couple of seconds like it's running out of fuel. It doesn't stall and straightens itself out in a few seconds and then everything's ok. It doesn't matter what my fuel level is. It just seems like when it sucks up that cold air in park it doesn't like it. Any ideas?
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