NATURAL GAS VEHICLE FUEL QUALITY/DRIVEABILITY (INFO.)

SUBJECT: NATURAL GAS VEHICLE FUEL QUALITY/DRIVEABILITY

MODEL and YEAR: 1992-93 C1, AND C2 WITH 5.7L ENGINES

When reviewing a driveability or engine power concern on C1, C2, trucks with a natural gas fueled engine, do not overlook fuel quality as a possible cause of the concern.

Water is almost always present in natural gas. Currently, there is not a General Motors or Federal Government standard regulating the acceptable amount of water in natural gas. C.A.R.B. (California Air Resources Board) has a limit of seven pounds maximum of water per one million cubic feet of natural gas. Conformance to this standard may be impossible for a dealer to determine but, if there is excessive water in the gas, the injectors and pressure regulator could be icing causing driveability and/or power problems.

Another fuel quality concern is the mixing of gases such as propane and nitrogen, or other gases which have a much lower octane number than natural gas. And the obvious, natural gas should not contain dust, sand, dirt, gums, oils, or other substances in an amount sufficient to be injurious to the vehicle being fueled.

Ask the operator if the truck is fueled at the same location as others in a fleet and if any other units are having similar problems? Does the truck go to more than one location for refueling? If so, is the driveability affected after refueling at one of these locations?

Be sure the fuel filter, located next to the fuel pressure regulator on the high pressure side, is clean and receiving recommended maintenance.

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.