DIESEL ENG. HARD HOT START INSUFFICIENT HEAT/FUEL

MODELS: 1978-81 C-1500 and 1983 CABALLERO W/RPO LF9-5.7L DIESEL ENGINE

Diesel engines may exhibit hard starting characteristics when they are shut down for some period of time after being fully warmed up. The cause is almost always lack of fuel or lack of heat to ignite the fuel.

The first step is to determine if it is a heat related condition or a fuel related condition. Normally, this can be determined by looking at the exhaust when the engine is being cranked.

Large quantities of white or light blue smoke coming out the exhaust is fuel vapor that did not ignite. If a large amount of white or blue smoke is present while cranking, the condition is most likely insufficient heat. If there is little or no white or light blue smoke, the cause is likely insufficient fuel.

The Service Manuals contain information regarding the diagnosis of diesel engines that are hard to start. Review the appropriate manual for diagnosis information. The following are items that are the most often overlooked, or, items that were not contained in the Service Manuals. This list is not a comprehensive list of all items that affect starting.

INSUFFICIENT HEAT

The following items affect the heat and must be corrected. Refer to the Service Manual for pro- cedures.

1. Cranking speed. Must be at least 240 RPM. Some tachometers are inaccurate at cranking speed. Compare the cranking speed of a car that will start with the car that does not start.

2. Dynamic timing. If timing is retarded beyond specifications, hard starting may be experienced.

3. Compression. Low compression may be experienced as a result of stuck rings. Stuck rings can be freed up with the use of a top engine cleaner as outlined below.

If stuck pistion rings are suspected to be the cause of excessive oil consumption, low compression, and/or excessive blowby on a diesel engine, the following procedure may be an effective correction:

1. With the engine warm, remove the glow plugs from all cylinders.

2. Equally divide the contents of one can of top engine cleaner (part number 1050002) into each cylinder. Allow the engine to soak for 24 hours with glow plugs removed.

3. Crank the engine with the glow plugs removed to expell the top engine cleaner.

4. Reinstall the glow plugs and start the engine.

INSUFFICIENT FUEL

1. Cranking speed. If the engine cranks too slow, injection pressures will not be high enough for ignition.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.