Chevrolet introduced the Impala in 1958. This Impala was offered in three trims -- the entry-level LS, the mid-grade LT and the fully loaded LTZ. The LS and LT were equipped with a 3.5-liter engine, while the LTZ was fitted with a 3.9-liter engine. When searching for timing specs for a vehicle, it is important to search by the model, model year and trim rather than just the model. Timing specs change from year to year, and different trims of a model might come with different engines, as is the case with the 2010 Impala. Manufacturers began introducing computerized, distributor-less ignition systems in the 1980s and those systems are universal today. As a result, the timing is not adjustable on newer vehicles.
An engine's firing order is the order in which the spark plugs fire to ignite a small explosion in the combustion chamber. In engines with a distributor, the firing order is determined by the order of the wires connecting the spark plugs to the distributor. In newer engines with Electronic Control Units (ECU), such as those found in the 2010 Impala, the ECU controls the firing order. The firing order for the 2010 Impala is 1-2-3-4-5-6, regardless of which V-6 engine it comes with. The firing order cannot be adjusted without replacing the ECU.
In ignition systems with distributors, the distributor can be adjusted so that all spark plugs fire when their corresponding piston is at Top Dead Center (TDC) or even slightly Before Top Dead Center (BTDC) to allow a few milliseconds for the fuel-oil mixture to ignite upon entering the piston's combustion chamber. The timing can be adjusted by turning the rotor and cap in the distributor by a few degrees. In newer cars, however, the timing is completely controlled by the ECU and the Ignition Control Unit (ICU). These are components of the on-board computer system and cannot be adjusted.
On traditional combustion engines with distributors, the timing mark on the distributor pulley shows where to set the timing so that it corresponds to the manufacturer's original setting. However, in vehicles with distributor-less ignitions, the mark is not adjustable. The 2010 Impala comes with a crankshaft position sensor that signals the computer system, which then adjusts the timing based on the vehicle's rpm output.
