Diagnostic Aids

Misfire index can be monitored using scan tool. Each cylinder has a misfire counter for current and history. Current misfire counter can be used to determine which cylinder is misfiring. Current misfire counter for a currently misfiring cylinder will be increased by a factor of 2. If VCM is unable to determine which cylinder is misfiring, counter will increase by a factor of one for each cylinder that may have misfired.

An intermittent misfire may be caused by spark plug wires, coil wires, contaminated fuel or low fuel level. Ensure spark plug wires are securely connected to spark plugs and distributor cap. Check wire routing for cross firing. If misfire occurs during damp weather, check for worn plug wires. Spray wires with water with engine running and check for spark to jump from wires. If spark is present, replace wires.

Check fuel condition and quality. Dirty or contaminated fuel could cause misfire condition. If fuel level is low, contaminates on bottom of tank could be introduced into fuel system. Severely out of balance tires could result in DTC setting. Road test vehicle and check for out of balance tires or drive line components.