6.6 LB7 LLY Diesel Hard Start/No Start Outside Temperature Below Freezing - kwfuel cold gelling wax hard additive smoke white blackprime ice water filter power P0087 P0093 P1093

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.

A 6.6 LB7 or LLY equipped vehicle may be brought in for a hard start or a no start only when outside temperatures are below freezing.

The customer may state the vehicle started, ran for a short period of time and then stalled out.

If the vehicle is moved into a heated shop or garage the vehicle will start normally.

If a below freezing hard start/no start has been verified, it may be caused by fuel contamination or poor fuel quality.

Open the fuel filter drain and get a large fuel sample out of the fuel filter. If water is found in the fuel system, it may cause a no start or hard start condition in below freezing temperatures. The water in the fuel system will freeze and restrict the fuel flow. During the condition monitor, the fuel system vacuum readings with the Kent-Moore fuel system gauge J44638 to diagnose the concern. Normal fuel system readings when cranking are 1 to 2 inches Hg (in/Hg) of vacuum. A frozen restricted fuel system can reach 10 in/Hg of vacuum or higher while cranking.

If no water is found in the fuel system, check the fuel API reading with the Kent-Moore J38641-B. The fuel API on winter blend fuels is approximately 35 to 44 depending on the location of the vehicle.

Fuel APIs below 35 to 44 would have a higher possibility of waxing or clouding in cold weather.

During the condition monitor, the fuel system vacuum readings with the Kent-Moore fuel system gauge J44638 to diagnose the concern. Normal fuel system readings when cranking are 1 to 2 in/Hg of vacuum. A waxed fuel system can reach 10 in/Hg of vacuum or higher while cranking.

Below is a test to help pinpoint the area of restriction:

1. Disconnect the fuel supply line at the quick connect over the left valve cover.
2. Install vacuum pump J23738-A to the chassis side fuel supply line.
3. Apply vacuum on the line in an effort to draw fuel from the fuel tank.
4. Note the vacuum required to pull fuel up through the fuel line.
5. If the vacuum is greater than 5 in/Hg (typically 15 to 20 in/Hg) to pull fuel from the tank than the restriction is either in the chassis lines or fuel tank pickup.
6. If the vacuum required to pull fuel from the fuel tank is low than 5 in/Hg than the issue is on the engine fuel supply side. In this case, follow published fuel system diagnostics in SI.

Note: This procedure must be completed in a timely manner (less than 50 min.) as to find the root cause.

Water may or may not be found in the fuel tank or fuel filter.

Note: Check the vehicle build date in GMVIS. If the vehicle was built between 1/21/2005 and 1/31/2005 the tank must be removed and inspected for signs of water. Vehicles built between these dates may have a slight amount of water left in the fuel tank from the fuel tank pressure testing procedures.

Complete current SI procedures for Fuel System Cleaning if water is found.

Bulletin Number 03-06-04-017 describes the use of fuel additives for water removal and cold weather operation. If large amounts of water or contamination are found in the fuel system follow the current SI procedures for Fuel System Cleaning.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

(01 02 03 04 05 LLY LB7 6.6 C2 C3 K2 K3 Chevrolet Silverado GMT800) and (01 02 03 04 05 LLY LB7 6.6 C2 C3 K2 K3 GMC Sierra GMT800)