PASSING THE BUCK
| 2000 Chevrolet Silverado 1500 Engine Buck Z
Question: I have a 2000 Silverado 5.3-liter 1500 2WD truck. The engine bucks at random speeds and shuts off randomly at stops or while turning. Plugs, wires, and fuel pump/filter have recently been changed. The mechanic told me it's running lean. It doesn't usually buck in the morning, but really acts up in the afternoon.
Answer: How did your mechanic determine the engine was running lean? When looking at the oxygen sensor voltage with a scan tool, you will actually see a lean condition (low voltage) induced by a misfire (bad plug, injector, etc.). Once a cylinder stops firing, the oxygen is no longer being burned, therefore there's lots of oxygen in the exhaust stream, and the powertrain control module deciphers this data as a lean condition. Your truck needs a step-by-step professional onceover. A technician should begin with a road test to duplicate the condition, scan the system for trouble codes and analyze incoming data/outgoing commands, review all relevant technical service bulletins and service news, then follow the appropriate diagnostic path where the information leads. If it's a true misfire, there may be a misfire code stored in the PCM memory. I would do my best to duplicate the misfire in the shop by "power braking" the engine, then perform a cylinder balance test. Narrowing down which cylinder is missing is half the battle. Here are a few issues that may or may not pertain to the problem: insufficient valve guide clearance causing a misfire (typically while towing), misfire caused by water in the fuel rail induced by the evap system, and stalling/rough idle due to excessive carbon buildup on the throttle plate.
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