Using a 1997 Chevy Express Scan Tool, you can pinpoint the root cause of engine problems. In this case, we’ll analyze high fuel trim readings. A scan tool reveals a total fuel trim of +23% for Bank 1 and +8% for Bank 2. The +23% reading for Bank 1 significantly exceeds acceptable limits, indicating the engine computer is compensating for a lean air-fuel mixture by adding excessive fuel.
Lean mixtures often cause misfires, which in turn, trigger lean readings from the oxygen sensors. Since common misfire causes have been ruled out, a lean air-fuel ratio is the likely culprit. Before assuming a Vortec injector issue, examine the voltage output of the four exhaust gas oxygen sensors.
With the engine fully warmed up at idle, observe the voltage readings from the upstream sensors (B1S1 and B2S1). These voltages should fluctuate between 0.1 and 0.8 volts. A graphing scan tool is ideal for visualizing this activity. A constant reading of 0.5 volts from any sensor suggests a problem with the sensor itself or its heater circuit. Increase the engine speed to 2,500-3,000 RPM to further assess sensor activity.
If either B1S1 or B2S2 shows a consistently low voltage (below 0.5V), try quickly tapping the throttle. This should briefly enrich the mixture, causing the voltage to rise toward 0.9V.
Disconnecting the Mass Air Flow (MAF) sensor might reveal improvement, though it’s less likely the primary issue. Remember, a clean OEM air filter and properly connected air intake tube are crucial for accurate MAF readings and proper fuel delivery.
