EXCESSIVE DETONATION CHECK OPERATION OF EGR

MODELS: 1986 S/T TRUCKS AND M VANS WITH 2.5L L4 ENGINES (VIN CODE E)

Some 1986 S/T trucks and M vans with a 2.5L L4 engine may exhibit excessive spark knock, at part throttle, due to an inoperative EGR valve.

If during diagnosis for the above condition an EGR valve has been diagnosed as inoperative because it does not respond to a normal vacuum signal, remove the vacuum hose and check the orifice in the vacuum fitting for a plugged condition (see Figure No. 1). Orifice inside diameter is .040" to .050". The orifice may have excessive, hardened hose assembly lubricant blocking it. If this condition exists, clear the orifice with a small wire, or pin, return the vacuum hose to the fitting and test the EGR valve for function. If the EGR is still inoperative, replace it.

Use applicable labor operation and labor time.

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.